WO2008145829A1 - Absolute radiation power measurement - Google Patents

Absolute radiation power measurement Download PDF

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Publication number
WO2008145829A1
WO2008145829A1 PCT/FI2008/050321 FI2008050321W WO2008145829A1 WO 2008145829 A1 WO2008145829 A1 WO 2008145829A1 FI 2008050321 W FI2008050321 W FI 2008050321W WO 2008145829 A1 WO2008145829 A1 WO 2008145829A1
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WO
WIPO (PCT)
Prior art keywords
detector
radiation
measuring
measuring arrangement
wavelength
Prior art date
Application number
PCT/FI2008/050321
Other languages
French (fr)
Inventor
Erkki Ikonen
Original Assignee
Teknillinen Korkeakoulu
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Teknillinen Korkeakoulu filed Critical Teknillinen Korkeakoulu
Priority to EP08761717.1A priority Critical patent/EP2160766A4/en
Publication of WO2008145829A1 publication Critical patent/WO2008145829A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02162—Coatings for devices characterised by at least one potential jump barrier or surface barrier for filtering or shielding light, e.g. multicolour filters for photodetectors
    • H01L31/02165—Coatings for devices characterised by at least one potential jump barrier or surface barrier for filtering or shielding light, e.g. multicolour filters for photodetectors using interference filters, e.g. multilayer dielectric filters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0232—Optical elements or arrangements associated with the device
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G01J1/0271—Housings; Attachments or accessories for photometers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G01J1/04—Optical or mechanical part supplementary adjustable parts
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G01J1/04—Optical or mechanical part supplementary adjustable parts
    • G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G01J1/04—Optical or mechanical part supplementary adjustable parts
    • G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
    • G01J1/0411—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings using focussing or collimating elements, i.e. lenses or mirrors; Aberration correction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/02—Details
    • G01J1/04—Optical or mechanical part supplementary adjustable parts
    • G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
    • G01J1/044—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings using shutters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/4257—Photometry, e.g. photographic exposure meter using electric radiation detectors applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0232—Optical elements or arrangements associated with the device
    • H01L31/02325—Optical elements or arrangements associated with the device the optical elements not being integrated nor being directly associated with the device

Definitions

  • the invention relates to radiation measurement technique in a general level.
  • the invention relates more specifically to radiation power determination according to the preamble of an independent method claim on measuring method.
  • the inven- tion relates also to detector according to the preamble of an independent detector claim.
  • the invention relates also to photodiode according to the preamble of an independent photodiode claim.
  • the invention relates also to measuring arrangement according to the preamble of an independent measuring arrangement claim.
  • the invention relates also to measuring system according to the preamble of an inde- pendent measuring system claim.
  • cryogenic radiometer appears to be the most accurate of the known devices.
  • Such technique provides a technique to measure optical power within a 100 ppm accu- racy by cooling the measuring device to low temperatures, to the temperatures of liquid helium, i.e. about 4 K.
  • the precision appears to be in a reasonable level for many applications, the liquid helium and the related cooling arrangement makes the measurements expensive while the equipment consumes energy for the cooling of the coolant which is also quite expensive as such.
  • heavy cooling apparatus can also influence on the portability and thus to the applicability of the instrumentation in portable, or almost portable devices.
  • DBR Distributed Bragg Reflector
  • a photo diode utilises pure silicon body, beneath an oxide layer area (considered as a region with a thickness), for the conversion from photon energy to electric energy that occurs mainly internally in the silicon body.
  • the oxide layer can be used as electrode for the photo diode.
  • EQE External Quantum Efficiency
  • the plateaus trap detector structure may improve the EQE
  • separate plates as detectors may be not only expensive as such, but their electrical properties may be different, if the plates are not made of the same batch and/or crystal, the mounting may be sensitive to the mounting errors and accuracy, even to minor deflecting ones, and diffuse reflectance of the radiation from the planar photodiodes may cause an uncertainty component which is difficult to estimate.
  • trap detectors are known to show increasing diffuse reflectance with time.
  • the invention relates to observation, that the measurement accuracy can be increased.
  • the detector with thick oxide layer on pure silicon body (and/or a natural inversion layer) can operate so that the IQE keeps very high within a certain oxide layer thickness range for a wavelength.
  • the invention relates to the improve- ment of the External Quantum Efficiency (also referred as EQE).
  • the product of IQE and EQE as closely to 1 or in per cents to 100 % as possible.
  • Detector according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent claim on photodiode.
  • Measuring method is characterized in that what has been stated in the characterizing part of an independent claim on measuring method.
  • Measuring arrangement is characterized in that what has been stated in the characterizing part of an independent claim on measuring arrangement.
  • Power meter according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent claim on power meter.
  • Photodiode according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent detector claim.
  • Measuring system is characterized in that what has been stated in the characterizing part of an independent system claim.
  • the preamble part to define the technical field of the claim and the characterizing part of a claim in the claims have been formally differentiated from each other by using at least one of the expressions: characterized in that, comprise and/or wherein, with a bolded font where applicable to the subject matter as whole, ac- cording to the way of saying and/or lingual deflection adapted to the context, but without any intention to limit the wholeness of the claim featured with features of technical field and/or the technical matter of the claim in a combination, made for the prosecution in such countries that demand two part claims, and in each claim to be interpreted for the application ownerDs interest
  • the way of marking is not made restricting rather than to improve readability in lingual sense, and to guide the reader to the correct technical field and/or patent classification.
  • radiation power is measured by measuring the current that originates from radiation photons to be converted to electron-hole pairs that constitute said current.
  • the radiation is brought at a Brewster angle to the surface layer, then into the detector body in which the quantum conversion of the photons to electron-hole pairs is to be occurring.
  • the angle of incidence is smaller, for a component of radiation having a wavelength and/or another feature of radiation, than the Brewster angle for a component of said radiation having the wavelength and another feature for radiation corresponding to the Brewster angle.
  • the angle of incidence is larger, for a component of radiation having a wavelength and/or another feature of radiation, than the Brewster angle for a component of said radiation having the wavelength and another feature for radiation corresponding to the Brewster angle.
  • a thin film structure on a substrate as arranged to receive the radiation at the Brewster angle can be used as an electrode for the detector, or as a surface on which further electrodes can be embedded so that the current from the quantum conversion can be measured.
  • the macroscopic beam as such may have internal variations for angles of propagation of certain modes of the beam and thus also to cause a variation in angle of incidence at the Brewster angle at the detector surface so that the direction representing angles from which they arrive to the detector surface may have a narrow distri- bution.
  • the detector surface may have a microstructure so that at least some of said modes and/or components of the radiation beam may appear to experience the angle of the incidence different than exactly the ideal Brewster angle were for an observer experiencing a macroscopic view.
  • the detector can be implemented by a semiconductor detector.
  • the detector can be optionally implemented by a tube comprising a filling, such as gas for instance, so that the tube is arranged to operate as detector.
  • the gas filling can operate as such as an absorber for certain wavelengths of radiation if some of such wavelengths were unwanted for an embodiment to meet the detector material on an inner sur- face of the tube.
  • the gas is in so low pressure that it is regarded as vacuum in practice.
  • the tube can be coated with a layered structure so to enhance the interaction of the introduced radiation in the layered structure and/or filling.
  • the coating is inside the tube, on the wall surface.
  • DinsideD should be understood as the side of a (by inder for example where the symmetry axis were in respect to the wall of a single cylinder, however, without limitation to the mere mentioned example.
  • the detector can comprise a detector arranged as a trap detector, but the detector material arranged to form such a de- tector which has a spherical or a spheroidal cross section.
  • a unite detector surface is mechanically stable, and/or electrically sufficiently uniform.
  • at lest one end comprises a sphere segment shaped detector material.
  • a detector tube comprises mirrors and/or several electrodes arranged to increase the external quantum efficiency yield.
  • the detector layers so form a roll in tube, for instance.
  • the tube can be in practical vacuum, but according to another embodiment the tube can have filling, which is made of gas so that the tube is arranged to be filled at least partly by the gas.
  • the tube comprises walls that allow the pressure of the gas to be used for modifying the optical density of the gas filling.
  • the detector comprising arrangement and/or the system can comprise pressure controlling means arranged to control the pressure (and/or temperature) at least at the surrounding volume where the radiation beam hits the detectorDs surface first time, i.e. where the influence of the
  • EQE has been about to end for the very incident beam part to the detectorDs so- face.
  • the detector can be at least partly coated with a layer filter to prevent an unwanted part of the radiation to get into the detector.
  • the detector can be at least partly coated with a layer structure that is arranged to prevent a wanted part of the radiation to get out of the detector.
  • the structure comprises a grating, mirror, DBR or a combination thereof.
  • the detector, the detector comprising arrangement and/or the system comprise temperature controlling means that means further comprise a Peltier element for controlling the temperature of the detector at the radiation input spot in/on the detector.
  • the temperature controlling means comprises additionally a heating means arranged to control the temperature at the radiation input spot into the detector into a pre-determined value.
  • the detector comprises a cavity, which is arranged for the absorption of the light directed to a surface of said cavity so for trapping the light.
  • the cavity means a volume that is filled at least partly with material that has a different structure and/or composition as the cavity walls.
  • a detector is implemented as it were forming a well into a silicon body so that said well extends into the silicon body so that the radiation beam meets the wall of the well in a Brewster angle at least once, but the specularly forwarded reflected pattern hits the well wall so that the beam would be approximating a spiral- like conical path into the deepness of the well.
  • the well can be made into a silicon crystal, but more advantageously onto a flexible substrate.
  • the ends of such a well can comprise a mirror and/or a suitable detector structure according to an embodiment of the invention.
  • a cavity according to an embodi- ment of the invention comprises at least a part that is arranged to operate as a DBR-structure for absorption of the radiation directed to a surface of said cavity.
  • the cavity is constituted by the silicon substrate body in which the radiation is arranged to be converted to the electron- hole pairs.
  • the filling of the cavity is a liquid substance filling at least partly the cavity.
  • the cavity can comprise multiple solid parts arranged to absorb radiation as the detector and so to operate as co-detectors.
  • the DBR-structure comprises a grating.
  • the DBR-structure is arranged to operate as diffraction optics, advantageously to keep the wanted part of the radiation to be measured in the detector.
  • the DBR-structure at least one of such is arranged on a substrate body, as a layer that comprises a number of sublayers.
  • the layer number is larger than 2.
  • the number of layers is larger than 10.
  • the number of layers is lar- ger than 20.
  • the number of layers is less than 100.
  • the number of layers is less than 300.
  • the layers are arranged to bend the radiation path towards the detectorDs ⁇ uch part in the body that is used in the conversion with the IQE.
  • the structure can be used in a reflector, with a curvature, made from silicon in order to increase the product of IQE and EQE for the reflector, so facilitating such a reflector to be used as a detector part in the conversion of radiation energy to electrical energy according to an embodiment of the invention.
  • the sub-layer structure can be used for to set the reflection properties with the sub-layer number for improving the product of IQE and EQE.
  • the sub-layer number is larger than 2.
  • the number of sub-layers is larger than 10.
  • the number of sub-layers is larger than 20.
  • the number of sub- layers is less than 100.
  • the number of layers is less than 300.
  • two DBR-structures are arranged on a substrate, for improvement of the product of IQE and EQE, according to one variant into a stack so that the stack comprises at least one layer in which the quantum conversion is aimed to happen, at least partly, but according to another variant the DBR structures can be different and they are so situated that they are not directly on each other in contact, but rather by a medium layer.
  • a first DBR structure with a first type but also a second DBR structure with a second type.
  • the first and/or second types of the DBR-structures are manufactured into the detector and can be arranged to be selected from a layered structure in an oxide layer, a layered structure on an oxide layer, a layered structure in an anti reflection coating layer, a layered structure on a reflection coating layer, a layered structure on a substrate body of the detector material, a layered structure between an antireflection coating on a substrate body of the detector material, a grating in oxide layer, another antireflection coating layer, a grating on a substrate body of the detector material, a grating between a substrate body of the detector material and an oxide layer, a mirroring surface at the edge of a detector body, or a part thereof arranged to direct oxide layer wave guide modes into the detector body, an anomaly in the substrate body, an anomaly in the oxide layer, and a cavity of the oxide layer to form a surface to direct photon radiation into the silicon body.
  • a first optical coefficient of refraction for a DBR-structure comprising the low reflectance material is selectable in range 1.0001 - 5.
  • a second optical coefficient of refraction for a DBR-structure comprising the high reflectance material is selectable in range 1.0001- 5, but higher or equal than said first optical coefficient, for the wave length in wavelength range in question.
  • the DBR structure is at least one of the following: said first DBR-structure and said second DBR-structure.
  • a DBR structure of a grating type is used for reflecting photon radiation back to the path leading to the detector body.
  • the cavity comprises at least a part that is arranged to operate as a Rayleigh horn type trap arranged to trap radiation for absorption of the radiation directed to a surface of said cavity.
  • the cavity comprises at least a part that is arranged to operate as a focusing mirror to focus radiation on to the radiation sensitive area of the detector or another part implemented by another cavity comprising the detector.
  • the mirror is implemented by a paraboloidal mirror or spherical mirror.
  • the detector is on a surface facing to the mirror and/or a cavity surface.
  • the detector material is arranged to be on the surface that has a shape of the mirror and/or said cavity surface, advantageously arranged for a focusing geometry, but according to an optional embodiment in a non-focussing geometry which can be at least a planar geometry or in suitable part a diverging geometry so to be arranged to deal with higher radiation fluxes, for embodiments and thus division of radiation power on a larger area than on that of the mirror.
  • a non-focussing geometry which can be at least a planar geometry or in suitable part a diverging geometry so to be arranged to deal with higher radiation fluxes, for embodiments and thus division of radiation power on a larger area than on that of the mirror.
  • the geometry is diverging
  • the cavity comprises at least on one surface an antireflection coating layer arranged to interact with the radiation to be absorbed, but arranged so that the layer actually guides photons back into the de- tector body for the conversion .
  • the detector comprises at least one film layer, but according to another embodiment many film layers.
  • the layer comprises Si, Ga, As, P, In, Sn, Pb, C, Ge or a combination of the just mentioned.
  • the detector according to an embodiment of the invention can be utilised in a layer thickness metering device.
  • Fig. 1 illustrates an embodiment of the invention
  • Fig. 2 illustrates a detail in an embodiment of the invention
  • Fig. 3 illustrates a detector surface structure according to an embodiment of the invention
  • Fig. 4 illustrate an adjustable detector surface structure according to an em- bodiment of the invention
  • Fig. 5 illustrates a detector surface structure according to an embodiment of the invention
  • Fig. 6 illustrates a detector surface structure according to an embodiment of the invention to provide a multilayer structure
  • Fig. 7 illustrates a detector system according to an embodiment of the invention
  • Fig. 8 illustrates a measurement system according to an embodiment of the invention
  • Fig. 9 illustrates a measurement method according to an embodiment of the invention
  • Fig. 1 OA illustrates reflection as a function of the angle of incidence for a 500 nm photon radiation reflected from a Si diode surface with various indicated oxide layer thicknesses
  • Fig. 10B illustrates reflection as a function of the angle of incidence for an 800 nm photon radiation reflected from a Si diode surface with various indicated oxide layer thicknesses
  • Fig. 10C demonstrates reflection as a function of the angle of incidence for photon radiation with the indicated wavelengths from Si diode surface with various indicated oxide layer thicknesses in range of 2900-2916 nm, and
  • Fig. 11 illustrates photon radiation passage in a Si diode.
  • the power of a photon radiation can be measured as measuring electric current in a suitable system, provided that the frequency f (or the wavelength) is known.
  • a current is provided, as- suming 100% EQE, according to (2):
  • the tyflle presents the yield after each various loss mechanisms, internal (IQE) and/or external (EQE) by the number of k that have a significance to the radiation power before the radiation is brought into the material that is supposed to generate the electron-hole pairs.
  • IQE internal
  • EQE external
  • the incident radiation can get absorbed into the photo detector, especially when the detector is made of silicon, so that at least 99 % of the p-polahzed photons are absorbed while arriving to the photo detector at the Brewster angle.
  • the oxide layer thickness has a tolerance of essentially smaller than 10 nm, advantageously smaller than 5 nm, but according to an optional embodiment smaller than 3 nm.
  • a tolerance applies for an area of an oxide layer having a thickness, which area can be a unite area that is smaller than 1 ⁇ m 2 , advantageously smaller than 1 mm 2 , more advantageously smaller than 1 cm 2 but preferably larger than at least ten per cents of the area of a single detector.
  • the tolerance applies to the surface in perpendicular direction to the surface with defects having a diameter in parallel direction of the surface less than a wave length of the radiation, but more advantageously less than 1/10 the wavelength.
  • a tolerance applies for an area that is a non-connected area as such to form detector parts.
  • the radiation used in the power measurement can be a fixed wavelength radiation.
  • common three wavelengths 790 nm, 633 and 488 cf. the wave lengths indicated in Fig 10C
  • a single structure comprising an ox- ide layer of 2908 nm on silicon.
  • Other suitable wavelengths are 529 nm, 576 and 703, or other fixed or non fixed radiation source wavelength, as a skilled man in the art can realize from the embodiments of the invention when read and understood the text, as well as the Examples .
  • the reflectance depends on the oxide layer thickness periodically for a first wave length with a first period, and for a sec- ond wave length with a second period, overlapping reflectance minima occurrences can form a resonance for the plurality of said wavelengths.
  • the oxide layer thickness can be utilised that corresponds occurrences of resonances of minimum reflectance with a fixed oxide layer thickness.
  • the radia- tion can be provided with suitable radiation source.
  • the antireflection coating has a very low opacity other than that of silicon dioxide in an optional embodiment of the invention.
  • the oxide layer thickness can be selected according to the oxide layer as above mentioned in respect to the desired wavelength.
  • a reference to example 1 is made.
  • at least one of the radiation sources is replaced by a versatile source to provide several wavelengths, but is used as a fixed radiation source with the corresponding wavelength.
  • the availability of ad- justable radiation sources may limit the selection of the thickness of the oxide layer, for the absolute radiation power measurement.
  • the approximate fraction of 0.1 % of the photons, as specularly and/or diffusively reflected, can be directed to a photo detector, i.e. photo diode for instance, made of suitable material.
  • the detector comprises a pure silicon body coated with a uniform oxide layer for example.
  • the directing of the incoming radiation can be made by means that are arranged to direct the radiation into the detector.
  • Such means can comprise collimating means implemented by lenses and/or pinholes.
  • One ensemble of embodiments comprise a cavity comprising same material on the cavity walls, as the above mentioned photo-detector is made of, but also in addition or optionally arranged to utilise a mirror that has a form of sphere segment and/or a shape of a paraboloid arranged to direct the radiation to the detector.
  • the mirror is made of photo detector material with suitable structure implementation so actually operating actually as a very poor re- fleeting mirror.
  • a spherical mirror is advantageous because the angular distribution of the diffusively reflected radiation and the reflectance provide means to determine the portion of the radiation that escapes from the input orifice through which the incident radiation is inputted, before the very first reflection in the detector, on the spot hitting the detector, and also means to provide an estimate for the loss in the reflection.
  • a paraboloid mirror can be used, so that the diffusively reflected light can be directed by the paraboloid mirror to a uni-directional path and so to measure the radiation with detectors situated in the plane of the element which had the first reflection of the inputted radiation.
  • Such a measurement yields sufficient information of the diffuse reflection of the photodiode, especially on the absolute value of the angular distribution.
  • An advan- tage of paraboloidal mirror can be utilised to achieve a well defined direction of the collected diffuse and thus back-reflected radiation towards the detector surface, so that the divergence of the back-reflected angle can be minimized, by using the col- limation properties of such a paraboloidal mirror, and thus so to have the angle in which the radiation meets the detector surface as well defined direction for the ra- diation, to direct the path of radiation from the surrounding volume of the detector into the detector by the mirror.
  • a solid state detector can be implemented by utilising a layered structure that comprises at least one layer in a plurality of layers, for which at least one layer is arranged to comprise oxide so that such wave guide modes that connect to the oxide layer due to the scattering are reflected back before their entry into the detector edge.
  • the reflector has been implemented by DBR.
  • the layered structure can be a mirror arranged to the edge of the oxide layer with a suitable tilt and/or curvature so to reflect the wave guide modes towards the detector body.
  • the reflector can be implemented by a periodic structure patterned in or on the oxide layer and/or the substrate.
  • Such a diffraction grating can reflect the wave guide modes back into the detector material, advantageously into the silicon body.
  • the wave guide modes are absorbed at the oxide layer edge into the surrounding detector body material.
  • the oxide layer can be embedded into the silicon substrate constituting the detector body.
  • the detector comprises a cavity in a silicon piece with the silicon oxide layer having thickness of antireflection coating for a photon radia- tion.
  • a periodic structure is arranged to operate for a wave length, but according to another embodiment to operate for at least one wave length, but also for more wavelengths.
  • the detector according to an embodiment of the invention as embodied by a photodiode for instance can be oper- ated in a radiometer in temperatures that are near the temperature of liquid (I) ni- trogen N(I), which is easy to handle in technical sense, the costs of the N(I)- coolant are lower and the cryogenic equipments consume less power for the cooling. Thus, the maintenance costs are lower and also the mechanical size can be smaller.
  • the radiometer can absorb the incoming light in a spot and the surrounding, so that the diffuse reflections can be controlled so contributing to a simple structure for the device, if compared to the technique in which several specular reflections were to be controlled.
  • a radiometer according to an em- bodiment can be manufactured for utilisation in several wave length ranges, provided that the thickness of the oxide layer on the silicon, in the corresponding embodiment, can be controlled within a tolerance of 10 nm, advantageously within a tolerance of 5 nm and even more preferably 2 nm or better.
  • a radiation source that has a laser can be used as the light source that has a tunable wavelength.
  • other radiation sources can be used, also fixed ones in one variant of an embodiment.
  • each desired wavelength to be used in the measurement can have each an own dedicated radiometer for the wavelength correspond- ing wavelength range so to comprise a system of radiometers.
  • a detector operable as a photodiode that comprises a thin film coating is arranged to improve the EQE of the photodiode for radiation coming into said thin film in a Brewster angle.
  • the detector structure in a photo-diode to be used in the detector has an oxide film on a substrate.
  • said substrate is silicon substrate.
  • the oxide is a silicon oxide.
  • said oxide comprises another substance in the oxide structure less than 10 20 atoms per mole of silicon atoms.
  • the detector comprises at least one further layer.
  • a detector according to an embodiment of the invention is used in a system according to an embodiment of the invention.
  • the system comprises also a radiation source for the radiation.
  • the radiation is monochromatic radiation.
  • the radiation is coherent radiation.
  • the radiation comprises at least two radiation components each having a predefined wave length.
  • the radiation comprises radiation that has components of less than a dozen of wavelengths from which at least one has a monochromatic and/or coherent feature.
  • the detector has been implemented by a semiconductor detector.
  • the detector has been implemented by a tube comprising a gas filling, so that the tube is arranged to operate as detector.
  • the detector comprises a cavity, which is arranged with detector material walls and detector structure arranged for the absorption of the light directed to a surface of said cavity.
  • the cavity comprises at least a part that is arranged to operate as a Rayleigh horn, or another kind of a trap, for absorption of the radiation directed to a surface of said cavity, to be used as a part of a trap detector according to an embodiment of the invention.
  • the cavity comprises at least a part that is arranged to operate as a DBR-structure for improve the IQE related absorption of the radiation directed to a surface of said cavity.
  • the cavity comprises at least a part that is arranged to operate as a well or as a Rayleigh horn for absorption of the radiation directed to a surface of said cavity.
  • the cavity comprises at least a part that is arranged to operate as a focusing mirror to focus radiation on to the radiation sensitive area of the detector or another part implemented by another cavity comprising the detector.
  • the mirror is implemented by a paraboloidal mirror or spherical mirror.
  • the incident beam meets the detector surface in the Brewster angle at the first time at the hit spot, in a plateaus part of the detector.
  • the detector comprises another part that is arranged in form of a spherical mirror to surround concentrically the hit spot. That another part comprises same detector materials arranged same way as the plateaus part. So, said another part actually operates as a poorly operating mirror, but very efficient de- tector, utilising the advantage of the optical geometry to reflect the non-absorbed minor part back to the plate having the hit spot.
  • the detector is arranged on a substrate body by a surface that is facing to the mirror and/or a cavity surface.
  • the mirror comprises bulbous layers arranged to absorb as many orders as possible of the reflected radiation between the layers of the bulbous structure.
  • at least one of the mirrors comprises a coating capable of act as the detector.
  • the detector material is arranged to be on the surface that has a shape of the mirror and/or said cavity surface in a focusing geometry, but according to an optional embodiment in a non-focussing geometry which can be at least a planar geometry or in suitable part a diverging geometry arranged to deal with higher radiation fluxes for division on a larger area than on that of the mirror.
  • the cavity comprises at least on one surface a silicon layer arranged to interact with the radiation to be absorbed. According to an embodiment of the invention the cavity comprises at least on one surface an antireflection coating layer arranged to interact with the radiation to be absorbed. According to an embodiment of the invention the cavity comprises at least on one surface an antireflection coating layer arranged to interact with the radiation to be absorbed.
  • the detector comprises at least one film layer. According to an embodiment the detector has at least two locations to form a diversified detector.
  • the layer to be used in the detector comprises at least Si and an oxide layer thereof.
  • the detector comprises alternatively or in addition to pure silicon and its oxide Ga, As, P, In, Sn, Pb, C, Ge or a combination of the mentioned.
  • Fig 1 illustrates an example according to an embodiment of the invention.
  • the radiation source 101 radiates radiation 102.
  • the radiation is coherent and/or monochromatic photon radiation.
  • the radiation is laser radiation.
  • the radiation is in optical range of visible light.
  • the radiation comprises a component from UV- and/or IR-range.
  • the radiation can be polarized radiation, for instance such as in a p-polarized laser beam.
  • the Brewster angled vacuum window 112 is arranged to pass the incoming radiation 102 into the detector volume 113 via the inlet part 111.
  • the window 112 is provided with preferably known and high efficiency.
  • Inlet part 111 comprises advantageously a valve 117 further comprising a control means 109 arranged to control the shutter means 110 so that the entrance of the radiation to the further parts can be stopped and/or prevented.
  • the shutter means can be implemented in an embodiment by a macroscopic means, but according to an embodiment of the invention the shutter 109 can be implemented by a liquid crystal means and/or mems-related micro lamels or rolls for the photon radiation related aspects.
  • At least one of the parts 111 and 113 comprises optionally or in addition advantageously also a sealing valve, which can be located for instance with the valve 117 to provide a joint point.
  • a sealing valve can be used when the parts 111 and 113 are arranged to be mutually detachable from each other, so to detach the part 113 from the part 111 without breaking the atmosphere in the part 113 and the pressure P, as in a practical vac- uum, can remain, even if the parts 111 and 113 were separated. That is an advantage when the part 113 is used in more than one location, or it is used to replace another suitable detector structure.
  • the detector 108 is a polarization detector arranged to detect the radiation after its entry into the part 111 after back-reflection from 107.
  • the detector can be arranged to detect s-polahzed light, and thus can be used to estimate back reflectance from an optical path leading to said detector, and so to estimate radiation that escapes from the detector in a geometry apparent from the figure.
  • the radiation beam 103 is of the same radiation origin as the radiation 102, but a different reference numeral is used to discriminate the parts of the (momentary) radiation path.
  • the radiation path comprises at least one of the following path parts 102, 103, 104, 105, 106 so depending on the position of the radiation source 101.
  • the point or hit spot of radiation beam to hit the detector surface is marked by item 104.
  • a reflection from the detector surface 118 (Fig 1 ) is indicated by the ray 105, which hit the mirror surface 107 at the spot of the arrow spike.
  • the items 106 illustrate some directions of diffuse reflection.
  • the angle of ray 103 is not exactly at the Brewster angle, but illustrated so only to indicate the existence of the ray 105 on the corresponding path to the shown direction.
  • the reflectance can be 99.5 % or better and the point is close to the position of specular reflection from 118.
  • the mirror 107 can be implemented by a surface having a reflectance that is equal or higher than 90%, provided that mirror does not have detector material and/or structure according to an embodiment.
  • the mirror 107 is made as to operate as detector with the structure and composition of a detector according to a suitable embodiment.
  • Fig 1 shows the operating temperature T in which the detector is supposed to be working according to an embodiment of the invention.
  • the pressure P is an ambient pressure.
  • the T is equal or more than 10 K.
  • the T is equal or more than 50 K.
  • the T is equal or more than 100 K.
  • the T is equal or less than 175 K.
  • the T is equal or less than 220 K
  • the T equals to boiling point of liquefied nitrogen at the corresponding pressure.
  • the detector volume 113 is kept in a vacuum, but so that the surrounding structures are kept in T by a coolant cooled to the said temperature.
  • vacuum means in order to evacuate the detector surrounding volume or a part thereof, vacuum means can be used to make and/or to maintain the vacuum, i.e. conditions in which there is less gaseous medium or media phase material present in the volume than in the ambient conditions.
  • the pressure P is less than about 0.1 Atm.
  • the pressure P is less than 0.01 Atm.
  • the pressure P is less than 0.001 Atm.
  • the pressure is higher than the pressure in intermolecular space in gas.
  • the radiation beam 103 is collimated by collimating means 114.
  • the colli- mating means 114 comprises a disk-like piece that has the part 116 so defining an opening and/or an orifice for the radiation to be collimated.
  • the collimating means can be embodied by tube-like means comprising the part 115 arranged to collimate the radiation beam 103.
  • the entrance aperture for the radiation 103 can be used for the collimation.
  • lenses and/or conventional mirrors can be used for collimating the radiation beam whose power is about to be meas- ured, optionally or in addition to the means 114 and/or means 116, to be used for arranging the beam to meet the detector in Brewster angle.
  • the mirror 107 can be embodied as a spherical reflector arranged to reflect the diffuse radiation to a spot on a detector for forming therein electron-hole pairs and thus contributing to the electrical current.
  • the spot 104 is the center of the spherical part 107.
  • the reflector can be optionally embodied by a paraboloidal surface.
  • the mirror has an opening for the entrance of the beam 103. According to an embodiment the opening is arranged so that the open- ing has a well known area with high accuracy and operates as a collimator part.
  • the spherical part can comprise planar mirrors and/or detectors in advantageous directions to increase the yield of the product of IQE and EQE towards 1.
  • the EQE is maximized.
  • the loss of the radiation in a reflection event is minimized optionally or in addition to EQE maximization.
  • the reflector 107 can comprise an area or region that is switchable to at least one of the states connected and non-connected as arranged to operate as a detector as the part 118 or to guide radiation at least in some extent to the detector part 118.
  • an area or region can be arranged in a forward direction of the radiation in its path after a first reflection, according to an embodiment also repeatedly to catch the specular reflections.
  • the reflector 107 can be made in such an embodiment cheaper than by making the whole 107 from detector material. So, the reflec- tor 107 can be manufactured by machining for instance, casting and coating or by a work.
  • the reflector can be arranged to have a coating with a detector material for using it as a detector and the related layers and/or DBR structures.
  • the 107 can be provided with a mirror surface and in an embodiment variant with non -uniformity locations embodied as detectors or as holes or other formations guiding the radiation to a detector.
  • the mirror 107 has, alternatively to an embodiment in which the 107 has mirror surface in conventional meaning, very large absorbance, preferably in the embodiment even the same as or as closely as practically possible as the absorbance of the detector part 118, so actually deflect- ing from the operation of an ordinary mirror, and so actually facilitating to convert to the mirror 107 incoming radiation photon energy according to its quantum efficiency to electric current so facilitating the yield increase also from that part of the radiation that could escape by several mechanisms from the 118 at the spot 104.
  • the mirror 107 so embodied can act as a secondary detector or a part of the detector, depending on the desired geometry and mirror type for the measurement.
  • the secondary detector 107 is used in the embodiment in question as a separately coupled or in parallel coupled with the detector 118.
  • Fig 4 gives further examples on such embodiments.
  • the Fig 1 embodies a cross section from such an embodiment that util- izes a spherical mirror 107
  • the cross section in the figure also demonstrates, that the mirror 107 could comprise a cylinder part formed curvature for the mirror, so that said cylinder has the axis at the point 104 extending parallel with the normal of the page at the point 104.
  • the mirror 107 is formed by such a cylinder, and the primary detector 118 and/or the input system for the collimated light is/are slightly tilted so that the part of the radiation that potentially escapes from the spot 104 from the first reflection is directed to the cylindrical mirror surface at a second point, on the mirror, but if there were still some even lesser part of the radiation to escape the mirror 107 because of reflection or scattering at said second point, the tilt of detector 118 is arranged so that the ra- diation were about as to experience an endless spiral like path in the maze until extinction in the mirroring occurrences has emptied the radiation from its capability to further conversions to electric current.
  • the mirror 107 as actually embodied as detector comprises a cylindrical form.
  • the detector part/mirror 107 has a form of ice-cream cone.
  • the detector part 118 can be designed to have a non-planar form for having the surface curvature of parabolic mirrors, used as such in telescopes, to focus the diffusively reflected and/or scattered rays better on to a certain point on the mirror 107 surface.
  • the mirror 107 has also at least one similar kind of part that is arranged as the detector 118 in a non-planar embodiment.
  • the cylinder has spheroidally or spherically curved ends so to keep the radiation reflected in multiple times as long as possible for a high yield EQE.
  • the mirror 107 can have plane like tilted or pivoted plates in suitable part as arranged to guide and/or increase the EQE of the detector.
  • the collimator means 114 are arranged so that some radiation after the collimation hit the mirror/detector 107 at the back side around the entrance opening and thus compensate a certain portion of the radiation that supposed to hit the mirror at opening location, so that the portion is defined by the geometry of the opening and the collimating means.
  • the mirror/detector comprises detector material arranged to convert the radiation photons to electron-hole pairs, but also outside side of the mirror/detector, supposing that the inside is the side of the location of the spot 104.
  • the outside side is considered to be the side that is opposite side of the mirror to the detector in an embodiment implemented with a mirror as the part 107.
  • said annular kind of a region is divided into parts, the current from each part can be measured and thus such divided parts can be used to generate a signal to control and concentrate the radiation beam into a desired position for entrance to the volume of detector, the volume defined by the mirror 107.
  • the mirror 107 comprises a similar coating as the detectorDs 118 surface, but is not limited to the mere similarityor equality.
  • the mirror part 107 and the detector part 118 can be connected together or separated so collecting the electric current jointly or separately, as demonstrated with the Fig 4.
  • the detector surface 118 and the mirror 107 surface area that is used as detector can be arranged to be connectable as illustrated in Fig 4 by the dashed line 402 to demonstrate a detector structure 400 according to an embodiment of the invention.
  • the current and/or a related quantity derivable from the current formed by the item 118 can be read by the interface 401 , which can further push the signal for signal processing and/or storing for the data and the related measurement data comprising the condition related data, as temperature, pressure, properties and/or features of the radiation.
  • the interface 401 operation can be controlled, which is indicated by the arrow directing towards the 401.
  • the interface can be used for the controlling of the connection 402.
  • the detector part 118 is arranged to be adjustable.
  • the adjusting is implemented mechanically, but according to another embodiment electrically.
  • the adjusting can be implemented hydraulically.
  • the detector is arranged pivotable around an axis, advantageously near the point 104, so avoiding potential vibrations of the detector and thus enhance the stability.
  • the 107 and 113 contain pluggable escape holes for the specular reflection.
  • the adjusting is arranged to optimize the detec- tor part position in respect for the Brewster angle as the angle of incidence for the radiation beam 103 to be measured.
  • the adjusting is made by electro-mechanical means, so comprising electrical and/or mechanical means.
  • the adjusting is made in a course of an optimization algorithm arranged to have maxi- mum current into an outer circuit as an indicator of the Brewster angle occurrence.
  • the optimization is made for minimum specular reflectance and/or the relating photocurrent.
  • said minimization is made simultaneously with said maximization, at least in some part having a phase which has overlapping there between, but ac- cording to an embodiment of the invention said minimization and said maximization are made independently on each other, for a part of a detector for instance.
  • said minimization and said maximization are made in a serial way with a first number of minimizations and a second number of maximizations in a sequence comprising respective sub sequences.
  • the sub-sequences are interlaced, at least partly.
  • the whole part 113 is arranged to be pivotable.
  • the part 111 is arranged to be pivotable with the part 113.
  • the part 111 can be locked with 113 for the pivoting.
  • the part 113 is arranged to be pivotable in respect to the part 111 at the joint point.
  • the joint point is implemented by a flexible joint.
  • the joint is made at the location of the part 117.
  • the pivoting as such is not limited only to mere horizontal or to mere vertical plane of such respective embodiments.
  • an adjusting / a certain optimization is made in a closed-loop principle, to adjust by a number of successive steps back and/or another number of successive steps forth in order to converge to meet the Brewster angle.
  • the steps can be implemented by defining the error still present to the desired angle until a predefined tolerance is met.
  • the implementation of the adjustment can comprise at its simplest form a scale for angles in the appropriate range and an adjustment knob with an influence on to the axis to vary the tilt of the detector for selecting the angle, as demonstrated in Fig 1 by the bending arrows at right from the 118.
  • the axis can be arranged to have a gear to have the range for suitably enhanced control accuracy.
  • Such an adjustment can be optionally or in suitable part additionally implemented with an electric motor combined to a mechanism to pivot the detectors tilt.
  • the adjustment is arranged by a stepper motor with a pitch between the positions, say for a non-limiting example with an increase/decrease step of 0.1 degrees or even less.
  • the tilting and/or pivoting of the axis and the tilt is controlled by a fluid pressure of a fluid bar having a first height at first angle and a second height at second angle of the detector tilt.
  • a fluid pressure of a fluid bar having a first height at first angle and a second height at second angle of the detector tilt.
  • Fig 2 illustrates a detail of detector that is embodied as a hexagonal photodiode as a detector 118 to show an example of a single photo diode with a substrate 201 , according to an embodiment of the invention.
  • the shape is not limited only to hex- agonal, nor is the number of photodiodes on the substrate 201 although just one is illustrated for clarity reasons.
  • Each of such photodiodes can be arranged for operation with a feature of radiation of its own.
  • at least one photodiode can be arranged to operate with multiple wavelengths. For instance, so that radiation wavelengths 488 nm, 633 nm, 790 nm, can be used with a single oxide layer having a thickness of 2908 nm on the silicon substrate.
  • the wave guide modes are reflected back before they hit the photodiode edge in an embodiment of the invention that utilises reflectors in the detector structure optionally or in addition to the curved mirror of 107.
  • the reflector can be arranged by a periodical pattern made in/on an oxide layer of the silicon substrate and/or in the silicon substrate itself.
  • Such a formation can be used as a Distributed Bragg Reflector, DBR for different wave lengths.
  • DBR is used in the photodi- ode.
  • the DBR has a first geometry 202 arranged to operate in the purpose.
  • the DBR has a second geometry 203 to operate in the purpose. According to an embodiment of the invention both can be used.
  • the arcs 203 in the figure can have a same centre of symmetry, but is not limited only there to.
  • the arcs illustrate to define a region in/on the detector that comprises a DBR-structure that is arranged to prevent and/or return photons back to the detector body.
  • DBR digital versatile disc
  • the arcs can comprise conical mirror structures or gratings that are arranged to keep the photons in the detector body.
  • the photo diode comprises at least a first geometry comprising DBR and/or a second geometry comprising DBR.
  • the photodiode 118 is designed for the purpose of the power measurement application so that 85 % of the Gaussian beam intensity fall to the area indicated by the dashed line 204, and 99,95 % of the Gaussian beam intensity fall to the area indicated by the dashed line 205, respectively representing values with two and four standard deviations.
  • Fig 3 illustrates a detector structure 300 according to an embodiment of the inven- tion.
  • the detector body material 107 and/or 118 is arranged to be under a layer
  • the layer 301 which can be implemented by a simple layer of antireflection coating.
  • the layer 301 can be an oxide layer in one embodiment, but in another embodiment it can be a metal coating layer. According to an embodiment of the invention the layer can be metal oxide layer. According to an embodiment of the invention the layer has a nano-crystalline structure. According to an embodiment of the inven- tion the layer comprises a halogen and/or a metal.
  • Fig 5 illustrates a detector structure 500 that comprises an oxide layer 501 and an intermediate layer 502.
  • the layer 502 comprises at least partly structures of DBR.
  • the layers can comprise structure and/or composition of a layer according to a layer 301 , 202, 203, 210, 211 , but is not limited only thereto or a certain combination of them.
  • Such structures can comprise grating, for instance.
  • the layer 502 drawn onto whole substrate may be not limited only that way, the part 501 and 118 and/or 107 can be in a connection, if not directly, as demonstrated in Fig 4.
  • the layer 502 is made controllable by the interface 401 to provide the functionality illustrated in Fig 4.
  • the layer 502 can implement the connection 402 of Fig 4 so that the layer 501 correspond the layer 107.
  • the layers 501 and 118 are not necessarily stacked on top of each other, i.e. the layer 502, 402 can comprise actually a semiconductor switch and/or the related wiring to the controlling in- terface and/or to couple the detector parts 107 and 118.
  • Fig 6 illustrates a detector structure 600 according to an embodiment of the invention that comprises several layers 601 , 602, 603 on the substrate 118.
  • the layers can comprise structure and/or composition of a layer according to a layer 301 , 202, 203, 210, 211 , but is not limited only thereto or a certain combination of them.
  • the layer 601 and/or 602 comprises an oxide layer and or a DBR layer.
  • a DBR layer can be arranged at least by one of the following items 202, 203, 210, 211 , as demonstrated in Fig 11.
  • the layer 603 comprises a transparent layer arranged in bulbous way to provide the mirror structure in which there are several mirrors 107.
  • the multilayer techniques can be used in for instance for the mirror 107, especially in embodiments in which the part 107 comprises detector body of silicon and a layer- structure on the detector body.
  • the part 107 comprises detector body of silicon and a layer- structure on the detector body.
  • at least one of the layers in Fig 6 is arranged in a bulbous way to comprise pure silicon arranged to act as a detector.
  • the inner (curvature centre side) side of the mirror 107 (see fig 1 ) is made and/or comprises a silicon layer of pure silicon arranged as an oxide free detector body at the very surface.
  • at least one of the other layers, in contact with said pure silicon layer forms an electrode for an outer circuit for photocurrent measurement.
  • Fig 7 illustrates a combined detector structure 700, in which there is a plurality of detectors, each having at least one detector having a detector structure, which detectors 200, 300, 400, 500, 600 are according to an embodiment of the invention so that each detector is comprising at least one detector with a detector structure (301 , 118, 107) that is at least partly same as the detector 100 according to an embodiment of the invention.
  • at least one of said detectors comprises a combination of at least two of detectors according to an embodiment with appropriate structures.
  • at least one of the structures comprises the structure 113 disclosed in Fig 1.
  • At least one of said detector structures is arranged to fit to a part 111 in Fig 1.
  • each of the detector structures in Fig 7 have fixed geometry for a certain fixed wavelength of radiation and thus a suitable thickness of the oxide layer 301 on the detector body 118, 107.
  • at least one of the detector structures is adjustable for adjusting the angle of the incidence.
  • the combined structure is arranged to have a replaceable detector structure to change one detector structure to another.
  • the replacement is im- plemented by a translator to change said detectors.
  • the detector structure 700 parts can be embodied in suitable part into a detector. According to an embodiment of the invention such a detector can be used in an arrangement to implement a method according to an embodiment of the invention, or in a device for the same.
  • Fig 8 illustrates a measurement system 800 according to an embodiment of the invention.
  • the system 800 comprises at least a detector structure 700 according to an embodiment of the invention.
  • the system 800 comprises the cryogenic arrangement 801 arranged to cool at least one detector of the detector structure 700 to its own operation temperature.
  • the system 800 comprises a photon source 101 arranged to provide the radiation whose radiation is to be measured.
  • the system 800 comprises vacuum pump 802 and the maintenance apparatus and related systems.
  • the system 800 comprises infrastructure providing apparatus 803 so providing the necessary amplifiers, interfaces and/or communi- cation lines as well as memory and processors to be used in the measurement data collection and/or controlling the measurements with the system 800.
  • the system 800 parts can be embodied in suitable part into a device.
  • the device is a portable device.
  • the de- vice is a solidly mountable device.
  • Fig 9 illustrates a method 900 according to an embodiment of the invention to be used for the absolute measurement of the power of radiation.
  • the quantum efficiency IQE and/or EQE can be measured and/or so to determine the ratio according to which the detector structure is capable to convert photons to electron-hole pairs, and/or estimating the EQE.
  • the phases are not necessary for each detector type for every measurement, provided that the detector structure (100, 113) of the type provides certain repeatability for the conversion ratio in set conditions.
  • the ratio, the quantum efficiency IQE and/or EQE can be determined also for several condi- tions of pressure and/or temperature conditions, as well as for other features of the radiation.
  • magnetic field can be used in the radiation wavelength modification for Zeeman-effect related modes of the radiation.
  • the method can comprise during the directing at least partly, a phase in which the radiation source is stabilized in radiation power.
  • the measuring method comprises a phase of determining a momentary power of said radiation, which can according to another embodiment comprise a phase of averaging of the measured quantity or a derivable quantity of such quantity measured.
  • the average can be arithmetic, geometric, harmonic, said average made according to as a gliding average or as an average of fixed interval during the data sampling or a weighted average.
  • the average can be taken over a wavelength range, power range, a time range or a combination of the mentioned as weighted for the result desired and/or the measurement condition details.
  • the incoming angle in which the radiation is introduced to the detector and can be defined with respect to the normal of the surface on the film layer is larger than Brewster angle of incoming radiation, but however so that it appears to be so because of the special curvature or another structure on the detector surface in an embodiment, because of the view point or a surface fine structure. Similar way, the incoming angle can appear as smaller than the Brewster angle, depending on the surface structure itself at the very point of the incoming radiation to hit the surface. Inside the radiation beam there might be also some minor divergence present between the modes of the radiation that has their path partly cross-wise the beam at the path.
  • the incoming radiation finally is arranged to come into the detector in the Brewster angle to meet the absorption and the related quantum efficiency apparent in the spoken geometry yielding an illustration of the deviating angle from the precise.
  • the radiation is directed in the phase of directing to the Brewster angle so that the radiation beam meets the detector structure in the Brewster angle and so facilitates the highest available absorption into the detector structure.
  • the measurement method implementation is not limited to any particular exemplified order of execution as such, but in suitable part method phases can overlap or they can be practiced in a different order, as in cyclic way embodied embodiments for example.
  • the measurement equipment can be allowed to stabilize before the exposing phase in the measurement.
  • the detector can be exposed to the radiation, for instance by opening a shutter so that the beam can enter the detector surface.
  • the temperature is controlled, preferably during the whole measurement to get the data in constant conditions of the tem- perature and/or pressure.
  • the temperature can be checked and controlled also in other parts than indicated.
  • the pressure P can be controlled, even so to fine tune the wavelength by using the relationship between the pressure and the wavelength.
  • the photon radiation is converted to electron-hole pairs with the internal quantum efficiency (IQE) defined rate.
  • IQE internal quantum efficiency
  • the current is measured to yield the power, by an outer circuit.
  • the conversion producing hole and/or electron current is measured and averaged in the averaging phase; at least on a part of the duty cycle of the radiation beam, the average is converted to power in a calculating phase, in which also anomalies of the reality from the ideal are to be estimated for the maximum accuracy.
  • the power measurement data is stored and/or reported for a further process- ing of the data.
  • phase duration may vary from an application or use to another, but is not limited in such a way.
  • there can be overlapping phases and circularly connected buffering can be used in order to increase the efficiency of the cycle for the measurement program to go through, for data acquisition and processing optimization for instance.
  • the measuring arrangement com- prises a vacuum part in the optical path of the radiation.
  • the detector can be sealed into a chamber so to avoid the environment gases to interact with the detector and/or the radiation incoming to the detector.
  • the whole part of the optical path from the radiation source to the detector is in vacuum, including in vacuum also mirrors, lenses and other po- tentially present correction means to direct the radiation along the desired path towards the detector surfaces.
  • the optical path can comprise a part with a dry gas filling in a pressure that is lower than the atmospheric pressure according to one embodiment, but according to another embodiment larger pressure P, say 1 ,5 ' 100 bars can be used for the gas for ad- justing the optical density of the medium in the 113.
  • the gas filling can be chosen so that it does not influence on the radiation at all, or, has a minimum influence as possible according to an embodiment in a low pressure.
  • the optical path can comprise a wave guide which is embodied as fibre or a liquid.
  • the fibre can be ar- ranged to comprise a cavity for stimulated emission, and thus as a source for the radiation.
  • optical path it may be advantageous to use very long optical path, i.e in cases which measure of power in conditions where the detector according to an embodiment of the invention is supposed to be used, but the optical path is at least partly non-accessible because of high temperature, a distance, an astronomical distance, or because of bio-hazard, or radioactive contamination originated radiation.
  • the optical path could at least partly comprise the medium between the source of the radiation to be used in the power measurement and the detector according to an embodiment of the invention.
  • n ⁇ is the refractive index of the first medium ⁇
  • n D is the refractive index of the second medium D
  • Dj 7 is the angle of incidence
  • Dh is the re- fraction angle calculated according to the SnellDs law.
  • the refractive indices may contain an imaginary part for media with absorption.
  • the order of subscripts ⁇ D indicates the direction of propagation of light at the interface.
  • the amplitude reflection coefficient of p polarized light for a thin film on a substrate is
  • Equation (7) is periodic in terms of the film thickness D with period
  • a silicon dioxide thin film on silicon substrate in vacuum is considered to be used as an example for an absolute power measurement with a reference to example 2 on the reflection coefficient angular dependence.
  • reflectances as a function of angle of incidence were calculated for a detector structure to be utilised for absolute power measurement for monochromatic wavelengths with the indicated thicknesses of the oxide layer.
  • the equations were used for optimization to achieve the maximum EQE at the minimum reflectance.
  • the optimization algorithm was used to drive an adjustment arrangement arranged to adjust the angle of incidence so that the beam meets the detector at Brewster angle.
  • a thin film thickness of D 2908 nm then produces low intensity reflection for p po- larized light at the Brewster angle for wavelengths . . . 488 nm, 529 nm, 576 nm, 633 nm, 703 nm, 790 nm ...
  • This result is useful since frequently used fixed laser wavelengths 488 nm and 633 nm can then be used with low reflection of the same thin film sample.
  • Such a favourable situation can be obtained because c/(488 nm)/d(633 nm) is close to the ratio 10/13. Similar ratios of small integers can be found for other multiplets of convenient laser wavelengths, which allows radiation power measurements at several fixed wavelengths using the same detector with angular adjustment at the desired wavelength.
  • Example 2 reflectance as a function of angle of incidence at certain wave- lengths
  • Fig. 1 OA and 1 OB respectively illustrate reflectance as a function of angle of incidence for a 500 nm (Fig 10A) and 800 nm (Fig 10B) photon radiation from a Si diode surface with various indicated oxide layer thicknesses according to the figure. Equations 5-8 shown in example 1 are used in the determinations. The oxide layer thickness is shown at the right hand side down corner in nanometers (nm). The radiation in the example was assumed to be p-polahzed for the indicated radiation. Although a curve appears to meet the zero reflectance, it does not in practice. It is also same way for the minima in the Figs 10B and 10C, too. This is because of non-zero imaginary part of the silicon substrate referactive index.
  • Fig. 10C demonstrates reflectance as a function of the angle of incidence for a Si diode surface with various indicated oxide layer thicknesses in range of 2900-2916 nm. The figure also helps to understand an embodiment of the invention that uses a larger thickness for the oxide layer for standard fixed laser wavelengths to be used in a detector that has a structure according to an example of Fig. 11 and/or Fig.1.
  • the photon radiation is indicated in Fig. 11 by ⁇ , ⁇ l, ⁇ 2 and ⁇ 3, in several aspects of the detector.
  • the point 104 is the reflection point of the inputted photons at a detector surface part.
  • the portion 105 of radiation is a forward reflected portion ⁇ l that can be stronger than the scattered rays 106.
  • the layer 301 is silicon dioxide layer, and the pure silicon body is indicated by the numerals 107 and 118.
  • the ⁇ 2 illustrates a wave guide mode propagating in the oxide layer. Such wave guide modes can appear into the oxide layer 301 because of scattering from atoms, dislocations and/or other imperfections potentially present in the structure.
  • the detector can in an embodiment of the invention have DBR structure (203) or a reflector (202, 210, and/or 211 ) that reflects the ⁇ 2 type photons into such a path that leads them into the pure silicon body 107.
  • a reflector 211 can be formed near the edge by a wedge cavity in the oxide layer.
  • Another kind of reflector can be formed by a dendrite ridge demon- strated by the serrated ridge cross section 210.
  • the DBR structure 203 is a periodic grating that can be present optionally or in addition to the 202.
  • the layer edges of the layer 301 can be rounded and polished so to reflect photons better back, and thus to the path leading into the pure silicon body 107.
  • the photon ⁇ 3 demonstrates a photon with photon energy that converts to electric energy in form of a photocurrent, appearing as the energy that belongs to the pair of electron and hole (e ⁇ , h + ).
  • the distance of the photon ⁇ 3 travelled can be quite long, even several hundreds of micrometers.
  • the detector body thickness can be that of a silicon wafer, in order about 0,5 mm, for the 118 and/or for the part 107 in an appropriate embodiment.
  • a detector structure has been embodied according to Fig. 1.
  • the detector struc- ture has a detector part 118 that has a silicon substrate body made of pure silicon in planar geometry.
  • the detector part 118 is arranged to be adjustable in respect to the entrance aperture for the beam 103 to enter at the Brewster angle in to the detector structure, so enabling to utilize the maximum EQE of the silicon body at the wavelength of the incoming radiation.
  • the spot 104 is in the center of the spherical part 107.
  • the part 107 is embodied as a mirror with very high reflectance as arranged to focus by reflection the diffuse radiation to a spot on a detector.
  • the spot does not necessarily be exactly the same as the spot 104 in which the diffuse and/or specular reflected beam parts are collected, especially in such an embodi- ment variant in which the part 107 does not move with the detector part 118.
  • the opening is arranged so that the opening has a well known area with high accuracy and operates as a collimator part. The reflected parts of the radiation are collected onto the detector part 118.
  • the detector structure comprises in addition to that shown in example 4 also a mirror at the oxide layer edge, DBR-structure, diffraction grating or a combination thereof so arranged that the modes of the radiation that propagate in the oxide layer in wave guide mode are directed into the silicon body to and/or back to the original direction to utilise the high IQE as much as possible.
  • Example 6 a mirror at the oxide layer edge, DBR-structure, diffraction grating or a combination thereof so arranged that the modes of the radiation that propagate in the oxide layer in wave guide mode are directed into the silicon body to and/or back to the original direction to utilise the high IQE as much as possible.
  • the set up is similar to that shown in example 4, but differs from that so that the mirror 107 has been replaced by a detector having the oxide layer and a silicon body structure but also the shape of the mirror 107 in example 4, and thus the de- tector is able to focus the reflected radiation as in example 4 back to the detector part 118, but can also operate as detector, so enhancing the EQE.
  • the detector part 107 can be coupled in parallel with the detector part 118.
  • the mirror 107 can act as a secondary detector or a part of the detector, depending on the desire the secondary detector 107 is used in the embodi- ment in question as a separately coupled or in parallel with the detector 118.
  • Fig 4 gives further examples on such embodiments.
  • At least one of the parts 118 and 107 has the detector structure comprising in addition to that shown in example 4 also a mirror at the oxide layer edge, DBR-structure, diffraction grating or a combination thereof so arranged that the modes of the radiation that propagate in the oxide layer in wave guide mode are directed into the silicon body to and/or back to the original direction to utilise the high IQE as much as possible.
  • At least one of the parts 118 and 107 is arranged to be tiltable/pivotable in respect to the entering beam 103 from the entrance opening for the beam to meet the detector part 118 in Brewster angle. Because of the aperture system for the entering beam, this means that in embodiments in which the aperture or opening for beam 103 has essentially the same cross section area, the 107 is advantageously moved along to the part 118 for the Brewster angle with the particular wavelength of the radiation beam 103.
  • the part 118 has locking means arranged to lock the geometry for the Brewster angle for the radiation at the wavelength.
  • the part 107 has locking means to lock according to the part 118 for the beam to meet the part 118 at the Brewster angle.
  • the detector piece 118 is arranged to be fixed but the 113 is arranged to move in respect to the 111 via a flexible joint 117.
  • the movement and/or fixation of the parts 113 and 111 in respect of each other are not limited as such.

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Abstract

The invention relates to an absolute power measurement to be made with high internal and/or external quantum efficiency to be utilised in a detector comprising at least one film layer (301 ) on a substrate (118) so forming a structure to guide radiation (γ), within a wave length in a wavelength range and means (202, 203) arranged to get at least part of said radiation (γ) absorbed in the detector body (118) by a conversion of the energy of said radiation photons (γ3) to energy of an electrical current (h+, e') in an operation temperature (T) of the detector. The invention relates also to a method, measuring arrangement and system to be used in accordance of said detector.

Description

Absolute Radiation Power Measurement
The invention relates to radiation measurement technique in a general level. The invention relates more specifically to radiation power determination according to the preamble of an independent method claim on measuring method. The inven- tion relates also to detector according to the preamble of an independent detector claim. The invention relates also to photodiode according to the preamble of an independent photodiode claim. The invention relates also to measuring arrangement according to the preamble of an independent measuring arrangement claim. The invention relates also to measuring system according to the preamble of an inde- pendent measuring system claim.
Sometimes it is needed very accurate power determination of photon radiation. For the purpose there exists a technique that is based on the conversion of the photon energy to electrical energy so that the photons of the radiation form electron-hole pairs in the detector, of a solid type. However, there is an existing prob- lem according to which the radiation when hitting the detector normally also yields a diffuse reflection. Even if the radiation were directed in a Brewster angle to the detector surface, some radiation deviates diffusively all around from the hit spot. In very accurate measurements of radiation power, known among the professionals as absolute radiation power measurement, the diffuse part of the radiation forms an uncertainty factor, if not directly measurable in the particular conditions. One problem relates also to the Internal Quantum Efficiency (IQE) of the material arranged to convert the radiation energy to energy of an electrical current.
It is known to improve the light absorption efficiency of a detector by mirrors. Such technique has been shown in US patent publication 5,281 ,804 by Shirasaki (1994) showing a mirror based structure to increase the absorption up to 96 per cent as shown therein. The known technique comprises some problems relating for instance to the direction determination of the incident angle of the radiation. Shirasaki suggests focusing the beam to a spot, which introduces uncertainty to the determination of the direction of the incident radiation. Oke et al in US 3,567,948 (1971 ) shows a spherical reflector as such arranged to focus and thus to improve the quantum efficiency of the detector.
One thing that influences the accurate measurements appears to be the thermal noise that can disturb the detector. Until the priority date of the current application, cryogenic radiometer appears to be the most accurate of the known devices. Such technique provides a technique to measure optical power within a 100 ppm accu- racy by cooling the measuring device to low temperatures, to the temperatures of liquid helium, i.e. about 4 K. Although the precision appears to be in a reasonable level for many applications, the liquid helium and the related cooling arrangement makes the measurements expensive while the equipment consumes energy for the cooling of the coolant which is also quite expensive as such. In addition, heavy cooling apparatus can also influence on the portability and thus to the applicability of the instrumentation in portable, or almost portable devices.
At the priority date of the current application (APDOCA), photodiodes as such have been used in one measurement related technique according to US 2004/0169245. Therein, a buried layer is provided as a Distributed Bragg Reflector (DBR) as such. The document suggests using DBR structure as a resonant cavity in photo detectors for enhancement of the silicon IQE and selectivity.
It is known to achieve almost 100% incident quantum efficiency within 1 ppm accuracy for a diode manufactured from silicon. At special conditions, with oxide layer on pure silicon body of the photodiode, and in temperature of 72 K the conversion of the energy of photons to energy in electrical form with sufficient accuracy has been proposed in theory as such. In such a high temperature technique, each photon that gets absorbed into the silicon body constitutes finally a pair of electron- hole and thus can constitute contribution to the corresponding photo current in to an outer circuit coupled with the diode. A photo diode utilises pure silicon body, beneath an oxide layer area (considered as a region with a thickness), for the conversion from photon energy to electric energy that occurs mainly internally in the silicon body. The oxide layer can be used as electrode for the photo diode. There is however a problem that part of the radiation flux can escape to enter into the structure of the photodiodeDs silicon body)f a known type, so yielding a low External Quantum Efficiency (EQE). This is tried to be mitigated by a trap detector, in which there are detector plates in the forward direction of the incident beam arranged to collect a part of the specularly reflected radiation from the photodiodes.
Although the plateaus trap detector structure may improve the EQE, separate plates as detectors may be not only expensive as such, but their electrical properties may be different, if the plates are not made of the same batch and/or crystal, the mounting may be sensitive to the mounting errors and accuracy, even to minor deflecting ones, and diffuse reflectance of the radiation from the planar photodiodes may cause an uncertainty component which is difficult to estimate. Further- more, trap detectors are known to show increasing diffuse reflectance with time. The invention relates to observation, that the measurement accuracy can be increased. The detector with thick oxide layer on pure silicon body (and/or a natural inversion layer) can operate so that the IQE keeps very high within a certain oxide layer thickness range for a wavelength. Also, the invention relates to the improve- ment of the External Quantum Efficiency (also referred as EQE).
Thus, it is a primary object of the invention to solve a problem how to get as much as possible of the energy of the incident photon radiation to be converted to energy in electric form to be measured for the power, i.e. to have the product of IQE and EQE as closely to 1 or in per cents to 100 % as possible. In other words, to minimize the uncertain part of the radiation energy and optionally or in addition to have the product of IQE and EQE as closely to 1 , or in per cents, to 100 % as possible. It is thus an object of the invention in accordance to the primary object to measure radiation with the IQE and EQE in optical range with equal or better accuracy than 50 ppm, but more preferably better than 10 ppm, and most preferably even better accuracy than 1 ppm, in a high temperature, provided that the accuracy presents an estimate to the loss according to which the product of IQE and EQE deflects from 1.
It is also an objective of the invention in accordance to the primary object to have controlled the diffuse reflection and/or scattering at the detector surface for the high product of IQE and EQE. In accordance to the primary object, it is also an objective of the invention to provide a detector implementation for the purpose. It is thus also an object of the invention to provide a detector that can be operated in cryogenic temperatures at least above 10 K but more preferably in high temperatures, that are even higher than 50 K, but potentially also in temperatures as high as or higher than 220 K with high product of IQE and EQE. It is also an object of the invention in accordance to the primary object to solve related known problems of the known technique and/or at least mitigate the influence of said problems. It is also an object of the invention to provide a measuring method to measure radiation power with high product of IQE and EQE. It is an object of the invention to provide devices in accordance to the primary object, detectors and/or power meters. Such are for example photodiodes for and power meters for the metering that are suitable for the measurements of radiation power with high product of IQE and EQE, and such that are at least new. Thus, it is also an object of the invention to provide in accordance to the primary object a measurement arrangement for the purpose with high product of IQE and EQE. It is also an object of the invention to provide a measurement system that utilizes devices according to the invention for the purpose with high product of IQE and EQE. A related objective within the scope of the primary objective is to make also more economical components available for such utilisation in which before one had to use expensive special components in the detector constructions.
Detector according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent claim on photodiode.
Measuring method according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent claim on measuring method.
Measuring arrangement according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent claim on measuring arrangement.
Power meter according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent claim on power meter.
Photodiode according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent detector claim.
Measuring system according to an embodiment of the invention is characterized in that what has been stated in the characterizing part of an independent system claim.
The preamble part to define the technical field of the claim and the characterizing part of a claim in the claims have been formally differentiated from each other by using at least one of the expressions: characterized in that, comprise and/or wherein, with a bolded font where applicable to the subject matter as whole, ac- cording to the way of saying and/or lingual deflection adapted to the context, but without any intention to limit the wholeness of the claim featured with features of technical field and/or the technical matter of the claim in a combination, made for the prosecution in such countries that demand two part claims, and in each claim to be interpreted for the application ownerDs interest The way of marking is not made restricting rather than to improve readability in lingual sense, and to guide the reader to the correct technical field and/or patent classification.
Further embodiments of the invention are indicated in the dependent claims. According to an embodiment of the invention, radiation power is measured by measuring the current that originates from radiation photons to be converted to electron-hole pairs that constitute said current. According to an embodiment of the invention the radiation is brought at a Brewster angle to the surface layer, then into the detector body in which the quantum conversion of the photons to electron-hole pairs is to be occurring.
According to an embodiment of the invention the angle of incidence is smaller, for a component of radiation having a wavelength and/or another feature of radiation, than the Brewster angle for a component of said radiation having the wavelength and another feature for radiation corresponding to the Brewster angle.
According to an embodiment of the invention the angle of incidence is larger, for a component of radiation having a wavelength and/or another feature of radiation, than the Brewster angle for a component of said radiation having the wavelength and another feature for radiation corresponding to the Brewster angle.
According to an embodiment of the invention a thin film structure on a substrate as arranged to receive the radiation at the Brewster angle can be used as an electrode for the detector, or as a surface on which further electrodes can be embedded so that the current from the quantum conversion can be measured.
In a beam, even as collimated according to an embodiment of the invention by mir- rors, lenses and/or a plurality of apertures comprising at least one aperture, the macroscopic beam as such may have internal variations for angles of propagation of certain modes of the beam and thus also to cause a variation in angle of incidence at the Brewster angle at the detector surface so that the direction representing angles from which they arrive to the detector surface may have a narrow distri- bution. Also, the detector surface may have a microstructure so that at least some of said modes and/or components of the radiation beam may appear to experience the angle of the incidence different than exactly the ideal Brewster angle were for an observer experiencing a macroscopic view.
According to an embodiment of the invention, collimating, instead of mere focusing onto a spot of the detector, yields better controllability over the precision to the angle of incidence for the radiation that is introduced into the detector according to an embodiment of the invention. According to an embodiment of the invention, the detector can be implemented by a semiconductor detector. According to an embodiment of the invention the detector can be optionally implemented by a tube comprising a filling, such as gas for instance, so that the tube is arranged to operate as detector. In a variant of an embodiment, the gas filling can operate as such as an absorber for certain wavelengths of radiation if some of such wavelengths were unwanted for an embodiment to meet the detector material on an inner sur- face of the tube. According to an embodiment of the invention the gas is in so low pressure that it is regarded as vacuum in practice. According to an embodiment of the invention the tube can be coated with a layered structure so to enhance the interaction of the introduced radiation in the layered structure and/or filling. According to an embodiment of the invention the coating is inside the tube, on the wall surface. In such a case the term DinsideD should be understood as the side of a (by inder for example where the symmetry axis were in respect to the wall of a single cylinder, however, without limitation to the mere mentioned example.
According to an embodiment of the invention, the detector can comprise a detector arranged as a trap detector, but the detector material arranged to form such a de- tector which has a spherical or a spheroidal cross section. According to an embodiment of the invention, such a unite detector surface is mechanically stable, and/or electrically sufficiently uniform. According to a variant of the embodiment at lest one end comprises a sphere segment shaped detector material.
According to an embodiment of the invention, a detector tube comprises mirrors and/or several electrodes arranged to increase the external quantum efficiency yield. According to an embodiment of the invention the detector layers so form a roll in tube, for instance. According to an embodiment, the tube can be in practical vacuum, but according to another embodiment the tube can have filling, which is made of gas so that the tube is arranged to be filled at least partly by the gas. Ac- cording to an embodiment the tube comprises walls that allow the pressure of the gas to be used for modifying the optical density of the gas filling. According to an embodiment of the invention the detector, the detector comprising arrangement and/or the system can comprise pressure controlling means arranged to control the pressure (and/or temperature) at least at the surrounding volume where the radiation beam hits the detectorDs surface first time, i.e. where the influence of the
EQE has been about to end for the very incident beam part to the detectorDs so- face.
According to an embodiment of the invention the detector can be at least partly coated with a layer filter to prevent an unwanted part of the radiation to get into the detector. According to an embodiment of the invention the detector can be at least partly coated with a layer structure that is arranged to prevent a wanted part of the radiation to get out of the detector. According to a variant of such an embodiment of the invention, the structure comprises a grating, mirror, DBR or a combination thereof. According to an embodiment of the invention the detector, the detector comprising arrangement and/or the system comprise temperature controlling means that means further comprise a Peltier element for controlling the temperature of the detector at the radiation input spot in/on the detector. According to another embodiment of the invention the temperature controlling means comprises additionally a heating means arranged to control the temperature at the radiation input spot into the detector into a pre-determined value.
According to an embodiment of the invention, the detector comprises a cavity, which is arranged for the absorption of the light directed to a surface of said cavity so for trapping the light. According to an embodiment of the invention the cavity means a volume that is filled at least partly with material that has a different structure and/or composition as the cavity walls. According to an embodiment of the in- vention, a detector is implemented as it were forming a well into a silicon body so that said well extends into the silicon body so that the radiation beam meets the wall of the well in a Brewster angle at least once, but the specularly forwarded reflected pattern hits the well wall so that the beam would be approximating a spiral- like conical path into the deepness of the well. According to an embodiment of the invention, the well can be made into a silicon crystal, but more advantageously onto a flexible substrate. According to an embodiment of the invention the ends of such a well can comprise a mirror and/or a suitable detector structure according to an embodiment of the invention.
According to an embodiment of the invention, a cavity according to an embodi- ment of the invention comprises at least a part that is arranged to operate as a DBR-structure for absorption of the radiation directed to a surface of said cavity.
According to an embodiment of the invention the cavity is constituted by the silicon substrate body in which the radiation is arranged to be converted to the electron- hole pairs.
According to an embodiment of the invention the filling of the cavity is a liquid substance filling at least partly the cavity. According to an embodiment of the invention the cavity can comprise multiple solid parts arranged to absorb radiation as the detector and so to operate as co-detectors. According to an embodiment of the invention the DBR-structure comprises a grating. According to an embodiment of the invention the DBR-structure is arranged to operate as diffraction optics, advantageously to keep the wanted part of the radiation to be measured in the detector.
According to an embodiment of the invention the DBR-structure, at least one of such is arranged on a substrate body, as a layer that comprises a number of sublayers. According to an embodiment of the invention the layer number is larger than 2. According to an embodiment of the invention the number of layers is larger than 10. According to an embodiment of the invention the number of layers is lar- ger than 20. According to an embodiment of the invention the number of layers is less than 100. According to an embodiment of the invention the number of layers is less than 300. According to an embodiment of the invention, the layers are arranged to bend the radiation path towards the detectorDsεuch part in the body that is used in the conversion with the IQE. According to an embodiment the structure can be used in a reflector, with a curvature, made from silicon in order to increase the product of IQE and EQE for the reflector, so facilitating such a reflector to be used as a detector part in the conversion of radiation energy to electrical energy according to an embodiment of the invention.
The sub-layer structure can be used for to set the reflection properties with the sub-layer number for improving the product of IQE and EQE. According to an embodiment of the invention, in a layer, the sub-layer number is larger than 2. According to an embodiment of the invention in a layer, the number of sub-layers is larger than 10. According to an embodiment of the invention, in a layer, the number of sub-layers is larger than 20. According to an embodiment of the invention, in a layer, the number of sub- layers is less than 100. According to an embodiment of the invention, in a layer, the number of layers is less than 300.
According to an embodiment of the invention, two DBR-structures are arranged on a substrate, for improvement of the product of IQE and EQE, according to one variant into a stack so that the stack comprises at least one layer in which the quantum conversion is aimed to happen, at least partly, but according to another variant the DBR structures can be different and they are so situated that they are not directly on each other in contact, but rather by a medium layer. In such a structure there is a first DBR structure with a first type, but also a second DBR structure with a second type. According to an embodiment of the invention the first and/or second types of the DBR-structures are manufactured into the detector and can be arranged to be selected from a layered structure in an oxide layer, a layered structure on an oxide layer, a layered structure in an anti reflection coating layer, a layered structure on a reflection coating layer, a layered structure on a substrate body of the detector material, a layered structure between an antireflection coating on a substrate body of the detector material, a grating in oxide layer, another antireflection coating layer, a grating on a substrate body of the detector material, a grating between a substrate body of the detector material and an oxide layer, a mirroring surface at the edge of a detector body, or a part thereof arranged to direct oxide layer wave guide modes into the detector body, an anomaly in the substrate body, an anomaly in the oxide layer, and a cavity of the oxide layer to form a surface to direct photon radiation into the silicon body.
According to an embodiment of the invention a first optical coefficient of refraction for a DBR-structure comprising the low reflectance material, is selectable in range 1.0001 - 5. According to an embodiment of the invention a second optical coefficient of refraction for a DBR-structure comprising the high reflectance material, is selectable in range 1.0001- 5, but higher or equal than said first optical coefficient, for the wave length in wavelength range in question.
According to an embodiment of the invention the DBR structure is at least one of the following: said first DBR-structure and said second DBR-structure. According to an embodiment of the invention a DBR structure of a grating type is used for reflecting photon radiation back to the path leading to the detector body.
According to an embodiment of the invention, the cavity comprises at least a part that is arranged to operate as a Rayleigh horn type trap arranged to trap radiation for absorption of the radiation directed to a surface of said cavity.
According to an embodiment of the invention, the cavity comprises at least a part that is arranged to operate as a focusing mirror to focus radiation on to the radiation sensitive area of the detector or another part implemented by another cavity comprising the detector. According to an embodiment of the invention, the mirror is implemented by a paraboloidal mirror or spherical mirror. According to an embodiment of the invention the detector is on a surface facing to the mirror and/or a cavity surface. According to an embodiment of the invention the detector material is arranged to be on the surface that has a shape of the mirror and/or said cavity surface, advantageously arranged for a focusing geometry, but according to an optional embodiment in a non-focussing geometry which can be at least a planar geometry or in suitable part a diverging geometry so to be arranged to deal with higher radiation fluxes, for embodiments and thus division of radiation power on a larger area than on that of the mirror. According to an embodiment of the invention in which the geometry is diverging, there is a surface arranged to collect the diverging radiation and/or interact with the radiation to be converted to electrical current so that the diffusively reflected part of the radiation has a contribution to the electric current to be used in the measurement.
According to an embodiment of the invention the cavity comprises at least on one surface an antireflection coating layer arranged to interact with the radiation to be absorbed, but arranged so that the layer actually guides photons back into the de- tector body for the conversion .
According to an embodiment of the invention the detector comprises at least one film layer, but according to another embodiment many film layers. According to an embodiment of the invention the layer comprises Si, Ga, As, P, In, Sn, Pb, C, Ge or a combination of the just mentioned.
According to an embodiment of the invention the detector according to an embodiment of the invention can be utilised in a layer thickness metering device.
Further embodiments of the invention are shown as examples in a non-restrictive manner in the following by a reference to the figures to be attached as a part of the description in which
Fig. 1 illustrates an embodiment of the invention,
Fig. 2 illustrates a detail in an embodiment of the invention,
Fig. 3 illustrates a detector surface structure according to an embodiment of the invention,
Fig. 4 illustrate an adjustable detector surface structure according to an em- bodiment of the invention,
Fig. 5 illustrates a detector surface structure according to an embodiment of the invention, Fig. 6 illustrates a detector surface structure according to an embodiment of the invention to provide a multilayer structure,
Fig. 7 illustrates a detector system according to an embodiment of the invention,
Fig. 8 illustrates a measurement system according to an embodiment of the invention,
Fig. 9 illustrates a measurement method according to an embodiment of the invention,
Fig. 1 OA illustrates reflection as a function of the angle of incidence for a 500 nm photon radiation reflected from a Si diode surface with various indicated oxide layer thicknesses,
Fig. 10B illustrates reflection as a function of the angle of incidence for an 800 nm photon radiation reflected from a Si diode surface with various indicated oxide layer thicknesses,
Fig. 10C demonstrates reflection as a function of the angle of incidence for photon radiation with the indicated wavelengths from Si diode surface with various indicated oxide layer thicknesses in range of 2900-2916 nm, and
Fig. 11 illustrates photon radiation passage in a Si diode.
The layer thicknesses as well as the geometrical ratios, other dimensions and/or angles between the items are not necessarily in the scale in the Figures (Fig). Same reference numerals are used in various above mentioned Figures to indicate similar kind of objects, which are not necessarily exactly equally the same, but can differ from each other from one to another and/or from a figure to another as a skilled man in the art understands from the context when read and understood the drawings, text and/or the related claims. Embodiments of the invention are combinable in suitable part.
The skilled persons in the art notice when read and understood the application that the Si used in the examples is only an example of a semiconductor, and thus a skilled person in the art knows that also other semiconductors that have similar phenomena for a collimated radiation beam to get absorbed in Brewster angle with high product of IQE and EQE can be used in suitable part for such embodiments. The power of a photon radiation can be measured as measuring electric current in a suitable system, provided that the frequency f (or the wavelength) is known.
A very coarse model, told as an example to demonstrate and to understand is shown. According to such, an incident photon flux coming to a detector to be con- sidered, comprising nph photons, per time interval At having energy of hf, define power P of the radiation for the photon flux according to (1 ):
(D P = nph %
Provided that the power is consumed in generating a number ne of electron-hole- pairs each comprising an opposite elementary charge e, a current is provided, as- suming 100% EQE, according to (2):
(2) l = nΛ At
Combining (1 ) and (2) yield
Figure imgf000013_0001
to define the external quantum efficiency η, or a conversion efficiency according to which the photons create electron-hole pairs in such conditions that the creation is overwhelmingly possible.
As the (4) applies, at least as a reasonable approximation,
(4) P = Pπ*ιabonYlηl , ι=0
the tyfllepresents the yield after each various loss mechanisms, internal (IQE) and/or external (EQE) by the number of k that have a significance to the radiation power before the radiation is brought into the material that is supposed to generate the electron-hole pairs. Thus, it is important to adjust the ratio PIPradmt,on according to embodiments of the invention as close as possible to 1. It is also important to use such a structure for the detector that also the ratio njnph were as close as possible to 1 , so also the product of IQE and EQE yield a high value near 1 , deviating less than 50 ppm but more preferably less than 5 ppm but most preferably less than 1 ppm. According to an embodiment of the invention, the incident radiation can get absorbed into the photo detector, especially when the detector is made of silicon, so that at least 99 % of the p-polahzed photons are absorbed while arriving to the photo detector at the Brewster angle. For instance, for a photo detector with an ox- ide layer on a silicon detector body, having the oxide layer thickness of 2908 nm, photons of laser radiation at the wavelengths of 488 nm, 633 nm and 790 nm can be received from a suitable angle of incidence to get absorbed, but most efficiently at the Brewster angle. According to an embodiment the oxide layer thickness has a tolerance of essentially smaller than 10 nm, advantageously smaller than 5 nm, but according to an optional embodiment smaller than 3 nm.
According to an embodiment a tolerance applies for an area of an oxide layer having a thickness, which area can be a unite area that is smaller than 1 μm2, advantageously smaller than 1 mm2, more advantageously smaller than 1 cm2 but preferably larger than at least ten per cents of the area of a single detector. According to an embodiment of the invention the tolerance applies to the surface in perpendicular direction to the surface with defects having a diameter in parallel direction of the surface less than a wave length of the radiation, but more advantageously less than 1/10 the wavelength. According to an embodiment of the invention a tolerance applies for an area that is a non-connected area as such to form detector parts.
According to an embodiment of the invention, the radiation used in the power measurement can be a fixed wavelength radiation. For example, according to an embodiment, common three wavelengths 790 nm, 633 and 488 (cf. the wave lengths indicated in Fig 10C) can be used with a single structure comprising an ox- ide layer of 2908 nm on silicon. Other suitable wavelengths are 529 nm, 576 and 703, or other fixed or non fixed radiation source wavelength, as a skilled man in the art can realize from the embodiments of the invention when read and understood the text, as well as the Examples . As the reflectance depends on the oxide layer thickness periodically for a first wave length with a first period, and for a sec- ond wave length with a second period, overlapping reflectance minima occurrences can form a resonance for the plurality of said wavelengths. So, for wavelengths 633 nm and 488 nm, as examples of common fixed wavelength radiation sources, the oxide layer thickness can be utilised that corresponds occurrences of resonances of minimum reflectance with a fixed oxide layer thickness. The radia- tion can be provided with suitable radiation source. According to an embodiment of the invention the antireflection coating has a very low opacity other than that of silicon dioxide in an optional embodiment of the invention.
A skilled man in the art can also realize that for a given fixed ensemble of wavelengths comprising at least one wavelength with similar resonances, the oxide layer thickness can be selected according to the oxide layer as above mentioned in respect to the desired wavelength. A reference to example 1 is made. However in an embodiment at least one of the radiation sources is replaced by a versatile source to provide several wavelengths, but is used as a fixed radiation source with the corresponding wavelength. At the short wavelength range the availability of ad- justable radiation sources may limit the selection of the thickness of the oxide layer, for the absolute radiation power measurement.
According to an embodiment of the invention the approximate fraction of 0.1 % of the photons, as specularly and/or diffusively reflected, can be directed to a photo detector, i.e. photo diode for instance, made of suitable material. According to an embodiment of the invention the detector comprises a pure silicon body coated with a uniform oxide layer for example. The directing of the incoming radiation can be made by means that are arranged to direct the radiation into the detector. Such means can comprise collimating means implemented by lenses and/or pinholes. One ensemble of embodiments comprise a cavity comprising same material on the cavity walls, as the above mentioned photo-detector is made of, but also in addition or optionally arranged to utilise a mirror that has a form of sphere segment and/or a shape of a paraboloid arranged to direct the radiation to the detector. According to an embodiment the mirror is made of photo detector material with suitable structure implementation so actually operating actually as a very poor re- fleeting mirror.
In an embodiment, utilisation of a spherical mirror is advantageous because the angular distribution of the diffusively reflected radiation and the reflectance provide means to determine the portion of the radiation that escapes from the input orifice through which the incident radiation is inputted, before the very first reflection in the detector, on the spot hitting the detector, and also means to provide an estimate for the loss in the reflection.
According to an embodiment of the invention, instead of using spherical mirror, a paraboloid mirror can be used, so that the diffusively reflected light can be directed by the paraboloid mirror to a uni-directional path and so to measure the radiation with detectors situated in the plane of the element which had the first reflection of the inputted radiation.
Such a measurement yields sufficient information of the diffuse reflection of the photodiode, especially on the absolute value of the angular distribution. An advan- tage of paraboloidal mirror can be utilised to achieve a well defined direction of the collected diffuse and thus back-reflected radiation towards the detector surface, so that the divergence of the back-reflected angle can be minimized, by using the col- limation properties of such a paraboloidal mirror, and thus so to have the angle in which the radiation meets the detector surface as well defined direction for the ra- diation, to direct the path of radiation from the surrounding volume of the detector into the detector by the mirror.
According to an embodiment of the invention, a solid state detector can be implemented by utilising a layered structure that comprises at least one layer in a plurality of layers, for which at least one layer is arranged to comprise oxide so that such wave guide modes that connect to the oxide layer due to the scattering are reflected back before their entry into the detector edge. According to an embodiment of the invention, the reflector has been implemented by DBR. According to an embodiment of the invention the layered structure can be a mirror arranged to the edge of the oxide layer with a suitable tilt and/or curvature so to reflect the wave guide modes towards the detector body. According to an embodiment of the invention the reflector can be implemented by a periodic structure patterned in or on the oxide layer and/or the substrate.
Such a diffraction grating can reflect the wave guide modes back into the detector material, advantageously into the silicon body. According to an embodiment of the invention the wave guide modes are absorbed at the oxide layer edge into the surrounding detector body material. In such an embodiment the oxide layer can be embedded into the silicon substrate constituting the detector body. According to an embodiment of the invention, the detector comprises a cavity in a silicon piece with the silicon oxide layer having thickness of antireflection coating for a photon radia- tion. According to an embodiment of the invention a periodic structure is arranged to operate for a wave length, but according to another embodiment to operate for at least one wave length, but also for more wavelengths.
According to an embodiment of the invention, the detector according to an embodiment of the invention as embodied by a photodiode for instance, can be oper- ated in a radiometer in temperatures that are near the temperature of liquid (I) ni- trogen N(I), which is easy to handle in technical sense, the costs of the N(I)- coolant are lower and the cryogenic equipments consume less power for the cooling. Thus, the maintenance costs are lower and also the mechanical size can be smaller.
In the detector according to an embodiment of the invention the radiometer can absorb the incoming light in a spot and the surrounding, so that the diffuse reflections can be controlled so contributing to a simple structure for the device, if compared to the technique in which several specular reflections were to be controlled.
According to an embodiment of the invention a radiometer according to an em- bodiment can be manufactured for utilisation in several wave length ranges, provided that the thickness of the oxide layer on the silicon, in the corresponding embodiment, can be controlled within a tolerance of 10 nm, advantageously within a tolerance of 5 nm and even more preferably 2 nm or better. According to another embodiment of the invention aimed for a multi wavelength embodiment implemen- tation by a single radiometer, a radiation source that has a laser can be used as the light source that has a tunable wavelength. Also other radiation sources can be used, also fixed ones in one variant of an embodiment. However, according to an embodiment of the invention each desired wavelength to be used in the measurement, can have each an own dedicated radiometer for the wavelength correspond- ing wavelength range so to comprise a system of radiometers.
According to an embodiment of the invention a detector operable as a photodiode that comprises a thin film coating is arranged to improve the EQE of the photodiode for radiation coming into said thin film in a Brewster angle. According to an embodiment of the invention, the detector structure in a photo-diode to be used in the detector, has an oxide film on a substrate. According to an embodiment of the invention said substrate is silicon substrate. According to an embodiment of the invention the oxide is a silicon oxide. According to an embodiment of the invention said oxide comprises another substance in the oxide structure less than 1020 atoms per mole of silicon atoms. According to another embodiment of the invention the detector comprises at least one further layer.
According to an embodiment of the invention, a detector according to an embodiment of the invention is used in a system according to an embodiment of the invention. According to an embodiment of the invention the system comprises also a radiation source for the radiation. According to an embodiment of the invention the radiation is monochromatic radiation. According to an embodiment of the invention the radiation is coherent radiation. According to an embodiment of the invention the radiation comprises at least two radiation components each having a predefined wave length. According to an embodiment of the invention the radiation comprises radiation that has components of less than a dozen of wavelengths from which at least one has a monochromatic and/or coherent feature.
Collimation, instead of mere focusing, according to an embodiment of the invention has better accuracy to the angle of incidence for the radiation than mere focussing. According to an embodiment of the invention the detector has been implemented by a semiconductor detector. According to an embodiment of the inven- tion the detector has been implemented by a tube comprising a gas filling, so that the tube is arranged to operate as detector. According to an embodiment of the invention, the detector comprises a cavity, which is arranged with detector material walls and detector structure arranged for the absorption of the light directed to a surface of said cavity.
According to an embodiment of the invention, the cavity comprises at least a part that is arranged to operate as a Rayleigh horn, or another kind of a trap, for absorption of the radiation directed to a surface of said cavity, to be used as a part of a trap detector according to an embodiment of the invention. According to an embodiment of the invention, the cavity comprises at least a part that is arranged to operate as a DBR-structure for improve the IQE related absorption of the radiation directed to a surface of said cavity. According to an embodiment of the invention, the cavity comprises at least a part that is arranged to operate as a well or as a Rayleigh horn for absorption of the radiation directed to a surface of said cavity.
According to an embodiment of the invention, the cavity comprises at least a part that is arranged to operate as a focusing mirror to focus radiation on to the radiation sensitive area of the detector or another part implemented by another cavity comprising the detector. According to an embodiment of the invention, the mirror is implemented by a paraboloidal mirror or spherical mirror.
According to an embodiment of the invention the incident beam meets the detector surface in the Brewster angle at the first time at the hit spot, in a plateaus part of the detector. The detector comprises another part that is arranged in form of a spherical mirror to surround concentrically the hit spot. That another part comprises same detector materials arranged same way as the plateaus part. So, said another part actually operates as a poorly operating mirror, but very efficient de- tector, utilising the advantage of the optical geometry to reflect the non-absorbed minor part back to the plate having the hit spot.
According to an embodiment of the invention the detector is arranged on a substrate body by a surface that is facing to the mirror and/or a cavity surface. Accord- ing to an embodiment of the invention the mirror comprises bulbous layers arranged to absorb as many orders as possible of the reflected radiation between the layers of the bulbous structure. According to an embodiment of the invention at least one of the mirrors comprises a coating capable of act as the detector.
According to an embodiment of the invention the detector material is arranged to be on the surface that has a shape of the mirror and/or said cavity surface in a focusing geometry, but according to an optional embodiment in a non-focussing geometry which can be at least a planar geometry or in suitable part a diverging geometry arranged to deal with higher radiation fluxes for division on a larger area than on that of the mirror.
According to an embodiment of the invention the cavity comprises at least on one surface a silicon layer arranged to interact with the radiation to be absorbed. According to an embodiment of the invention the cavity comprises at least on one surface an antireflection coating layer arranged to interact with the radiation to be absorbed. According to an embodiment of the invention the cavity comprises at least on one surface an antireflection coating layer arranged to interact with the radiation to be absorbed.
According to an embodiment of the invention the detector comprises at least one film layer. According to an embodiment the detector has at least two locations to form a diversified detector.
According to an embodiment of the invention the layer to be used in the detector comprises at least Si and an oxide layer thereof. According to an optional embodiment of the invention the detector comprises alternatively or in addition to pure silicon and its oxide Ga, As, P, In, Sn, Pb, C, Ge or a combination of the mentioned.
Fig 1 illustrates an example according to an embodiment of the invention. In the arrangement for the measurement of radiation power, the radiation source 101 radiates radiation 102. In an embodiment of the invention the radiation is coherent and/or monochromatic photon radiation. According to an embodiment of the invention the radiation is laser radiation. According to an embodiment the radiation is in optical range of visible light. According to an embodiment of the invention the radiation comprises a component from UV- and/or IR-range. According to an example, the radiation can be polarized radiation, for instance such as in a p-polarized laser beam.
The Brewster angled vacuum window 112 is arranged to pass the incoming radiation 102 into the detector volume 113 via the inlet part 111. The window 112 is provided with preferably known and high efficiency. Inlet part 111 comprises advantageously a valve 117 further comprising a control means 109 arranged to control the shutter means 110 so that the entrance of the radiation to the further parts can be stopped and/or prevented. The shutter means can be implemented in an embodiment by a macroscopic means, but according to an embodiment of the invention the shutter 109 can be implemented by a liquid crystal means and/or mems-related micro lamels or rolls for the photon radiation related aspects.
According an embodiment of the invention, at least one of the parts 111 and 113 comprises optionally or in addition advantageously also a sealing valve, which can be located for instance with the valve 117 to provide a joint point. Such a sealing valve can be used when the parts 111 and 113 are arranged to be mutually detachable from each other, so to detach the part 113 from the part 111 without breaking the atmosphere in the part 113 and the pressure P, as in a practical vac- uum, can remain, even if the parts 111 and 113 were separated. That is an advantage when the part 113 is used in more than one location, or it is used to replace another suitable detector structure.
The detector 108 is a polarization detector arranged to detect the radiation after its entry into the part 111 after back-reflection from 107. According an embodiment of the invention the detector can be arranged to detect s-polahzed light, and thus can be used to estimate back reflectance from an optical path leading to said detector, and so to estimate radiation that escapes from the detector in a geometry apparent from the figure.
The radiation beam 103 is of the same radiation origin as the radiation 102, but a different reference numeral is used to discriminate the parts of the (momentary) radiation path. The radiation path comprises at least one of the following path parts 102, 103, 104, 105, 106 so depending on the position of the radiation source 101. The point or hit spot of radiation beam to hit the detector surface is marked by item 104. A reflection from the detector surface 118 (Fig 1 ) is indicated by the ray 105, which hit the mirror surface 107 at the spot of the arrow spike. The items 106 illustrate some directions of diffuse reflection. As can be seen from the Fig, the angle of ray 103 is not exactly at the Brewster angle, but illustrated so only to indicate the existence of the ray 105 on the corresponding path to the shown direction. However, at the point so indicated, the reflectance can be 99.5 % or better and the point is close to the position of specular reflection from 118. According to an embodiment of the invention the mirror 107 can be implemented by a surface having a reflectance that is equal or higher than 90%, provided that mirror does not have detector material and/or structure according to an embodiment. According to an optional embodiment of the invention the mirror 107 is made as to operate as detector with the structure and composition of a detector according to a suitable embodiment.
Fig 1 shows the operating temperature T in which the detector is supposed to be working according to an embodiment of the invention. According to an embodiment of the invention the pressure P is an ambient pressure. According to an embodiment of the invention the T is equal or more than 10 K. According to another embodiment of the invention the T is equal or more than 50 K. According to an- other embodiment of the invention the T is equal or more than 100 K. According to an embodiment of the invention the T is equal or less than 175 K. According to an embodiment of the invention the T is equal or less than 220 K According to a preferred embodiment of the invention the T equals to boiling point of liquefied nitrogen at the corresponding pressure. According to an embodiment of the invention, the detector volume 113 is kept in a vacuum, but so that the surrounding structures are kept in T by a coolant cooled to the said temperature.
According to an embodiment of the invention in order to evacuate the detector surrounding volume or a part thereof, vacuum means can be used to make and/or to maintain the vacuum, i.e. conditions in which there is less gaseous medium or media phase material present in the volume than in the ambient conditions. So, according to an embodiment of the invention the pressure P is less than about 0.1 Atm. According to another embodiment of the invention the pressure P is less than 0.01 Atm. According to another embodiment of the invention the pressure P is less than 0.001 Atm. According to an embodiment of the invention the pressure is higher than the pressure in intermolecular space in gas. According to an embodiment of the invention the radiation beam 103 is collimated by collimating means 114. According to an embodiment of the invention the colli- mating means 114 comprises a disk-like piece that has the part 116 so defining an opening and/or an orifice for the radiation to be collimated. Optionally or in addition to the disk-like means comprising item 116, the collimating means can be embodied by tube-like means comprising the part 115 arranged to collimate the radiation beam 103. Also the entrance aperture for the radiation 103 can be used for the collimation. According to an embodiment also lenses and/or conventional mirrors can be used for collimating the radiation beam whose power is about to be meas- ured, optionally or in addition to the means 114 and/or means 116, to be used for arranging the beam to meet the detector in Brewster angle.
As can be seen from the cross-sectional view of the Fig 1 , the mirror 107 can be embodied as a spherical reflector arranged to reflect the diffuse radiation to a spot on a detector for forming therein electron-hole pairs and thus contributing to the electrical current. According to an embodiment of the invention the spot 104 is the center of the spherical part 107. According to an embodiment of the invention the reflector can be optionally embodied by a paraboloidal surface. According to an embodiment of the invention, the mirror has an opening for the entrance of the beam 103. According to an embodiment the opening is arranged so that the open- ing has a well known area with high accuracy and operates as a collimator part. According to an embodiment the spherical part can comprise planar mirrors and/or detectors in advantageous directions to increase the yield of the product of IQE and EQE towards 1. According to an embodiment of the invention the EQE is maximized. However, according to an embodiment of the invention the loss of the radiation in a reflection event is minimized optionally or in addition to EQE maximization.
According to an embodiment variant of the invention, the reflector 107 can comprise an area or region that is switchable to at least one of the states connected and non-connected as arranged to operate as a detector as the part 118 or to guide radiation at least in some extent to the detector part 118. Advantageously, such an area or region can be arranged in a forward direction of the radiation in its path after a first reflection, according to an embodiment also repeatedly to catch the specular reflections. Thus the reflector 107 can be made in such an embodiment cheaper than by making the whole 107 from detector material. So, the reflec- tor 107 can be manufactured by machining for instance, casting and coating or by a work. In suitable embodiment the reflector can be arranged to have a coating with a detector material for using it as a detector and the related layers and/or DBR structures. According to an embodiment of the invention the 107 can be provided with a mirror surface and in an embodiment variant with non -uniformity locations embodied as detectors or as holes or other formations guiding the radiation to a detector.
According to an embodiment of the invention the mirror 107 has, alternatively to an embodiment in which the 107 has mirror surface in conventional meaning, very large absorbance, preferably in the embodiment even the same as or as closely as practically possible as the absorbance of the detector part 118, so actually deflect- ing from the operation of an ordinary mirror, and so actually facilitating to convert to the mirror 107 incoming radiation photon energy according to its quantum efficiency to electric current so facilitating the yield increase also from that part of the radiation that could escape by several mechanisms from the 118 at the spot 104. In other words, the mirror 107 so embodied can act as a secondary detector or a part of the detector, depending on the desired geometry and mirror type for the measurement. The secondary detector 107 is used in the embodiment in question as a separately coupled or in parallel coupled with the detector 118. Fig 4 gives further examples on such embodiments.
Although the Fig 1 embodies a cross section from such an embodiment that util- izes a spherical mirror 107, the cross section in the figure also demonstrates, that the mirror 107 could comprise a cylinder part formed curvature for the mirror, so that said cylinder has the axis at the point 104 extending parallel with the normal of the page at the point 104. In a further embodiment of the invention, the mirror 107 is formed by such a cylinder, and the primary detector 118 and/or the input system for the collimated light is/are slightly tilted so that the part of the radiation that potentially escapes from the spot 104 from the first reflection is directed to the cylindrical mirror surface at a second point, on the mirror, but if there were still some even lesser part of the radiation to escape the mirror 107 because of reflection or scattering at said second point, the tilt of detector 118 is arranged so that the ra- diation were about as to experience an endless spiral like path in the maze until extinction in the mirroring occurrences has emptied the radiation from its capability to further conversions to electric current. Of course, in such a kind of a trap detector, the mirror 107 as actually embodied as detector comprises a cylindrical form. According to one embodiment the detector part/mirror 107 has a form of ice-cream cone. According to an embodiment of the invention, the detector part 118 can be designed to have a non-planar form for having the surface curvature of parabolic mirrors, used as such in telescopes, to focus the diffusively reflected and/or scattered rays better on to a certain point on the mirror 107 surface. According to a still further embodiment, the mirror 107 has also at least one similar kind of part that is arranged as the detector 118 in a non-planar embodiment. According to an em- bodiment of the invention the cylinder has spheroidally or spherically curved ends so to keep the radiation reflected in multiple times as long as possible for a high yield EQE. According to an embodiment of the invention the mirror 107 can have plane like tilted or pivoted plates in suitable part as arranged to guide and/or increase the EQE of the detector.
According to a further embodiment of the invention the, the collimator means 114 are arranged so that some radiation after the collimation hit the mirror/detector 107 at the back side around the entrance opening and thus compensate a certain portion of the radiation that supposed to hit the mirror at opening location, so that the portion is defined by the geometry of the opening and the collimating means.
In an embodiment the mirror/detector comprises detector material arranged to convert the radiation photons to electron-hole pairs, but also outside side of the mirror/detector, supposing that the inside is the side of the location of the spot 104. In such an embodiment the outside side is considered to be the side that is opposite side of the mirror to the detector in an embodiment implemented with a mirror as the part 107. Provided that said annular kind of a region is divided into parts, the current from each part can be measured and thus such divided parts can be used to generate a signal to control and concentrate the radiation beam into a desired position for entrance to the volume of detector, the volume defined by the mirror 107.
According to an embodiment of the invention, there are at least two similar mirrors arranged as the bulbous layers to increase the radiation absorption and thus the contribution to the electric current.
According to an embodiment of the invention the mirror 107 comprises a similar coating as the detectorDs 118 surface, but is not limited to the mere similarityor equality. According to an embodiment of the invention the mirror part 107 and the detector part 118 can be connected together or separated so collecting the electric current jointly or separately, as demonstrated with the Fig 4.
According to an embodiment of the invention the detector surface 118 and the mirror 107 surface area that is used as detector, can be arranged to be connectable as illustrated in Fig 4 by the dashed line 402 to demonstrate a detector structure 400 according to an embodiment of the invention. According to an embodiment of the invention the current and/or a related quantity derivable from the current formed by the item 118 can be read by the interface 401 , which can further push the signal for signal processing and/or storing for the data and the related measurement data comprising the condition related data, as temperature, pressure, properties and/or features of the radiation. The interface 401 operation can be controlled, which is indicated by the arrow directing towards the 401. According to an embodiment of the invention the interface can be used for the controlling of the connection 402.
According to an embodiment of the invention the detector part 118 is arranged to be adjustable. According to an embodiment the adjusting is implemented mechanically, but according to another embodiment electrically. According to an embodiment the adjusting can be implemented hydraulically. According to an em- bodiment of the invention the detector is arranged pivotable around an axis, advantageously near the point 104, so avoiding potential vibrations of the detector and thus enhance the stability. According to an embodiment of the invention the 107 and 113 contain pluggable escape holes for the specular reflection. According to an embodiment of the invention the adjusting is arranged to optimize the detec- tor part position in respect for the Brewster angle as the angle of incidence for the radiation beam 103 to be measured. According to an embodiment of the invention, the adjusting is made by electro-mechanical means, so comprising electrical and/or mechanical means. According to an embodiment of the invention the adjusting is made in a course of an optimization algorithm arranged to have maxi- mum current into an outer circuit as an indicator of the Brewster angle occurrence. According to an embodiment of the invention the optimization is made for minimum specular reflectance and/or the relating photocurrent. According to an embodiment said minimization is made simultaneously with said maximization, at least in some part having a phase which has overlapping there between, but ac- cording to an embodiment of the invention said minimization and said maximization are made independently on each other, for a part of a detector for instance. According to an embodiment of the invention said minimization and said maximization are made in a serial way with a first number of minimizations and a second number of maximizations in a sequence comprising respective sub sequences. According to an embodiment of the invention the sub-sequences are interlaced, at least partly. According to an embodiment of the invention, the whole part 113 is arranged to be pivotable. According to an embodiment of the invention, the part 111 is arranged to be pivotable with the part 113. According to an embodiment of the invention the part 111 can be locked with 113 for the pivoting. According to an embodiment of the invention, the part 113 is arranged to be pivotable in respect to the part 111 at the joint point. According to an embodiment of the invention the joint point is implemented by a flexible joint. According to an embodiment the joint is made at the location of the part 117. The pivoting as such is not limited only to mere horizontal or to mere vertical plane of such respective embodiments.
According to an embodiment an adjusting / a certain optimization is made in a closed-loop principle, to adjust by a number of successive steps back and/or another number of successive steps forth in order to converge to meet the Brewster angle. According to an embodiment of the invention the steps can be implemented by defining the error still present to the desired angle until a predefined tolerance is met.
Mechanically, the implementation of the adjustment can comprise at its simplest form a scale for angles in the appropriate range and an adjustment knob with an influence on to the axis to vary the tilt of the detector for selecting the angle, as demonstrated in Fig 1 by the bending arrows at right from the 118. For a suitable precision the axis can be arranged to have a gear to have the range for suitably enhanced control accuracy. Such an adjustment can be optionally or in suitable part additionally implemented with an electric motor combined to a mechanism to pivot the detectors tilt. According to an embodiment the adjustment is arranged by a stepper motor with a pitch between the positions, say for a non-limiting example with an increase/decrease step of 0.1 degrees or even less.
According to an embodiment the tilting and/or pivoting of the axis and the tilt is controlled by a fluid pressure of a fluid bar having a first height at first angle and a second height at second angle of the detector tilt. Such a mechanical embodiment with fluid may be demanding and comparatively expensive to implement with the fluid flow controls, but however, could yield a smooth movement between the angles.
Fig 2 illustrates a detail of detector that is embodied as a hexagonal photodiode as a detector 118 to show an example of a single photo diode with a substrate 201 , according to an embodiment of the invention. The shape is not limited only to hex- agonal, nor is the number of photodiodes on the substrate 201 although just one is illustrated for clarity reasons. Each of such photodiodes can be arranged for operation with a feature of radiation of its own. According to an embodiment of the invention at least one photodiode can be arranged to operate with multiple wavelengths. For instance, so that radiation wavelengths 488 nm, 633 nm, 790 nm, can be used with a single oxide layer having a thickness of 2908 nm on the silicon substrate.
Because of the scattering into the waveguide modes energy is coupled to propagate in the oxide layer of the photodiode. The wave guide modes are reflected back before they hit the photodiode edge in an embodiment of the invention that utilises reflectors in the detector structure optionally or in addition to the curved mirror of 107. The reflector can be arranged by a periodical pattern made in/on an oxide layer of the silicon substrate and/or in the silicon substrate itself. Such a formation can be used as a Distributed Bragg Reflector, DBR for different wave lengths. According to an embodiment of the invention DBR is used in the photodi- ode. According to an embodiment of the invention the DBR has a first geometry 202 arranged to operate in the purpose. According to another embodiment of the invention the DBR has a second geometry 203 to operate in the purpose. According to an embodiment of the invention both can be used.
The arcs 203 in the figure can have a same centre of symmetry, but is not limited only there to. According to an embodiment of the invention the arcs illustrate to define a region in/on the detector that comprises a DBR-structure that is arranged to prevent and/or return photons back to the detector body. A skilled man in the art realizes from the embodiment of the invention that also other shapes can be used for DBR to keep the edge-approaching photons in the detector body. According to an embodiment the arcs can comprise conical mirror structures or gratings that are arranged to keep the photons in the detector body. According to an embodiment of the invention the photo diode comprises at least a first geometry comprising DBR and/or a second geometry comprising DBR. The DBRs are discussed more in relation to Fig. 11. According to an embodiment of the invention the photodiode 118 is designed for the purpose of the power measurement application so that 85 % of the Gaussian beam intensity fall to the area indicated by the dashed line 204, and 99,95 % of the Gaussian beam intensity fall to the area indicated by the dashed line 205, respectively representing values with two and four standard deviations.
Fig 3 illustrates a detector structure 300 according to an embodiment of the inven- tion. The detector body material 107 and/or 118 is arranged to be under a layer
301 , which can be implemented by a simple layer of antireflection coating. The layer 301 can be an oxide layer in one embodiment, but in another embodiment it can be a metal coating layer. According to an embodiment of the invention the layer can be metal oxide layer. According to an embodiment of the invention the layer has a nano-crystalline structure. According to an embodiment of the inven- tion the layer comprises a halogen and/or a metal.
Fig 5 illustrates a detector structure 500 that comprises an oxide layer 501 and an intermediate layer 502. According to an embodiment of the invention the layer 502 comprises at least partly structures of DBR. In an embodiment, the layers can comprise structure and/or composition of a layer according to a layer 301 , 202, 203, 210, 211 , but is not limited only thereto or a certain combination of them. Such structures can comprise grating, for instance. Although the layer 502 drawn onto whole substrate, may be not limited only that way, the part 501 and 118 and/or 107 can be in a connection, if not directly, as demonstrated in Fig 4. According to an embodiment of the invention the layer 502 is made controllable by the interface 401 to provide the functionality illustrated in Fig 4. In such an embodiment the layer 502 can implement the connection 402 of Fig 4 so that the layer 501 correspond the layer 107. In such embodiment, the layers 501 and 118 are not necessarily stacked on top of each other, i.e. the layer 502, 402 can comprise actually a semiconductor switch and/or the related wiring to the controlling in- terface and/or to couple the detector parts 107 and 118.
Fig 6 illustrates a detector structure 600 according to an embodiment of the invention that comprises several layers 601 , 602, 603 on the substrate 118. In an embodiment, the layers can comprise structure and/or composition of a layer according to a layer 301 , 202, 203, 210, 211 , but is not limited only thereto or a certain combination of them. According to an embodiment of the invention the layer 601 and/or 602 comprises an oxide layer and or a DBR layer. A DBR layer can be arranged at least by one of the following items 202, 203, 210, 211 , as demonstrated in Fig 11. According to an embodiment of the invention the layer 603 comprises a transparent layer arranged in bulbous way to provide the mirror structure in which there are several mirrors 107. According to an embodiment of the invention, the multilayer techniques can be used in for instance for the mirror 107, especially in embodiments in which the part 107 comprises detector body of silicon and a layer- structure on the detector body. According to a variant of an embodiment of the invention at least one of the layers in Fig 6 is arranged in a bulbous way to comprise pure silicon arranged to act as a detector. According to an embodiment of the invention the inner (curvature centre side) side of the mirror 107 (see fig 1 ) is made and/or comprises a silicon layer of pure silicon arranged as an oxide free detector body at the very surface. According to an embodiment, at least one of the other layers, in contact with said pure silicon layer, forms an electrode for an outer circuit for photocurrent measurement.
Fig 7 illustrates a combined detector structure 700, in which there is a plurality of detectors, each having at least one detector having a detector structure, which detectors 200, 300, 400, 500, 600 are according to an embodiment of the invention so that each detector is comprising at least one detector with a detector structure (301 , 118, 107) that is at least partly same as the detector 100 according to an embodiment of the invention. According to an embodiment of the invention at least one of said detectors comprises a combination of at least two of detectors according to an embodiment with appropriate structures. According to an embodiment of the invention there are at least two or more redundant detectors in the structures according to an embodiment of the invention in said ensemble. According to an embodiment of the invention at least one of the structures comprises the structure 113 disclosed in Fig 1. According to an embodiment of the invention at least one of said detector structures is arranged to fit to a part 111 in Fig 1. According to an embodiment each of the detector structures in Fig 7 have fixed geometry for a certain fixed wavelength of radiation and thus a suitable thickness of the oxide layer 301 on the detector body 118, 107. According to an embodiment of the invention at least one of the detector structures is adjustable for adjusting the angle of the incidence. According to an embodiment of the invention the combined structure is arranged to have a replaceable detector structure to change one detector structure to another. According to an embodiment of the invention, the replacement is im- plemented by a translator to change said detectors.
According to an embodiment of the invention, the detector structure 700 parts can be embodied in suitable part into a detector. According to an embodiment of the invention such a detector can be used in an arrangement to implement a method according to an embodiment of the invention, or in a device for the same.
Fig 8 illustrates a measurement system 800 according to an embodiment of the invention. The system 800 comprises at least a detector structure 700 according to an embodiment of the invention. According to an embodiment of the invention the system 800 comprises the cryogenic arrangement 801 arranged to cool at least one detector of the detector structure 700 to its own operation temperature. Ac- cording to an embodiment of the invention the system 800 comprises a photon source 101 arranged to provide the radiation whose radiation is to be measured. According to an embodiment of the invention the system 800 comprises vacuum pump 802 and the maintenance apparatus and related systems. According to an embodiment of the invention the system 800 comprises infrastructure providing apparatus 803 so providing the necessary amplifiers, interfaces and/or communi- cation lines as well as memory and processors to be used in the measurement data collection and/or controlling the measurements with the system 800.
According to an embodiment of the invention, the system 800 parts can be embodied in suitable part into a device. According to an embodiment of the invention the device is a portable device. According to an embodiment of the invention the de- vice is a solidly mountable device.
Fig 9 illustrates a method 900 according to an embodiment of the invention to be used for the absolute measurement of the power of radiation. As a preparational phase, the quantum efficiency IQE and/or EQE can be measured and/or so to determine the ratio according to which the detector structure is capable to convert photons to electron-hole pairs, and/or estimating the EQE. According to an embodiment of the invention the phases are not necessary for each detector type for every measurement, provided that the detector structure (100, 113) of the type provides certain repeatability for the conversion ratio in set conditions. The ratio, the quantum efficiency IQE and/or EQE can be determined also for several condi- tions of pressure and/or temperature conditions, as well as for other features of the radiation.
According to an embodiment of the invention, magnetic field can be used in the radiation wavelength modification for Zeeman-effect related modes of the radiation.
The method can comprise during the directing at least partly, a phase in which the radiation source is stabilized in radiation power.
According to an embodiment of the invention the measuring method comprises a phase of determining a momentary power of said radiation, which can according to another embodiment comprise a phase of averaging of the measured quantity or a derivable quantity of such quantity measured. According to an embodiment the average can be arithmetic, geometric, harmonic, said average made according to as a gliding average or as an average of fixed interval during the data sampling or a weighted average. According to an embodiment the average can be taken over a wavelength range, power range, a time range or a combination of the mentioned as weighted for the result desired and/or the measurement condition details.
According to an embodiment of the invention, the incoming angle in which the radiation is introduced to the detector and can be defined with respect to the normal of the surface on the film layer, is larger than Brewster angle of incoming radiation, but however so that it appears to be so because of the special curvature or another structure on the detector surface in an embodiment, because of the view point or a surface fine structure. Similar way, the incoming angle can appear as smaller than the Brewster angle, depending on the surface structure itself at the very point of the incoming radiation to hit the surface. Inside the radiation beam there might be also some minor divergence present between the modes of the radiation that has their path partly cross-wise the beam at the path.
So, as in a different scale or view point due to the radiation geometry would yield an indication to meet the phenomena to occur at a different angle that deviates from the Brewster angle, the incoming radiation finally is arranged to come into the detector in the Brewster angle to meet the absorption and the related quantum efficiency apparent in the spoken geometry yielding an illustration of the deviating angle from the precise.
For an example on the measurement implementation, the radiation is directed in the phase of directing to the Brewster angle so that the radiation beam meets the detector structure in the Brewster angle and so facilitates the highest available absorption into the detector structure. The measurement method implementation is not limited to any particular exemplified order of execution as such, but in suitable part method phases can overlap or they can be practiced in a different order, as in cyclic way embodied embodiments for example. The measurement equipment can be allowed to stabilize before the exposing phase in the measurement. The detector can be exposed to the radiation, for instance by opening a shutter so that the beam can enter the detector surface. The temperature is controlled, preferably during the whole measurement to get the data in constant conditions of the tem- perature and/or pressure. The temperature can be checked and controlled also in other parts than indicated. The pressure P can be controlled, even so to fine tune the wavelength by using the relationship between the pressure and the wavelength. In the converting phase the photon radiation is converted to electron-hole pairs with the internal quantum efficiency (IQE) defined rate. According to an em- bodiment of the invention the current is measured to yield the power, by an outer circuit. The conversion producing hole and/or electron current is measured and averaged in the averaging phase; at least on a part of the duty cycle of the radiation beam, the average is converted to power in a calculating phase, in which also anomalies of the reality from the ideal are to be estimated for the maximum accuracy. The power measurement data is stored and/or reported for a further process- ing of the data.
The order of the phases indicated may be different in suitable part in embodiments, and some phases can be occurring in an overlapping manner with one or several other phases. The phase duration may vary from an application or use to another, but is not limited in such a way. In addition, especially in cases where several detectors are being used in combination, there can be overlapping phases and circularly connected buffering can be used in order to increase the efficiency of the cycle for the measurement program to go through, for data acquisition and processing optimization for instance.
According to an embodiment of the invention the measuring arrangement com- prises a vacuum part in the optical path of the radiation. In such an embodiment the detector can be sealed into a chamber so to avoid the environment gases to interact with the detector and/or the radiation incoming to the detector. Especially in such embodiment the whole part of the optical path from the radiation source to the detector is in vacuum, including in vacuum also mirrors, lenses and other po- tentially present correction means to direct the radiation along the desired path towards the detector surfaces. According to an embodiment of the invention the optical path can comprise a part with a dry gas filling in a pressure that is lower than the atmospheric pressure according to one embodiment, but according to another embodiment larger pressure P, say 1 ,5 ' 100 bars can be used for the gas for ad- justing the optical density of the medium in the 113. Optionally, the gas filling can be chosen so that it does not influence on the radiation at all, or, has a minimum influence as possible according to an embodiment in a low pressure.
According to an embodiment the optical path can comprise a wave guide which is embodied as fibre or a liquid. According to an embodiment the fibre can be ar- ranged to comprise a cavity for stimulated emission, and thus as a source for the radiation.
In some cases, it may be advantageous to use very long optical path, i.e in cases which measure of power in conditions where the detector according to an embodiment of the invention is supposed to be used, but the optical path is at least partly non-accessible because of high temperature, a distance, an astronomical distance, or because of bio-hazard, or radioactive contamination originated radiation. In such cases the optical path could at least partly comprise the medium between the source of the radiation to be used in the power measurement and the detector according to an embodiment of the invention.
Example 1.
Fresnel reflection and transmission coefficients for p polarized light at the interface between two media μ and Dare (μ, D= 1 , 2, 3, . . .)
« ,, COS θ^ — ϊ! .. CϋS θ., r*» = r; ,, cos θ ^u- i- fϊ ., cos r;, (5)
and
(6)
V =
respectively, where n^ is the refractive index of the first medium μ, nDis the refractive index of the second medium D, Dj7 is the angle of incidence, and Dh is the re- fraction angle calculated according to the SnellDs law. The refractive indices may contain an imaginary part for media with absorption. The order of subscripts μD indicates the direction of propagation of light at the interface. The amplitude reflection coefficient of p polarized light for a thin film on a substrate is
Figure imgf000033_0001
where subscripts 1 , 2, and 3 of the Fresnel coefficients refer to the medium above the thin film, to the thin film, and to the substrate. Parameter D = /cn2Dcos D2 is defined in terms of the thickness D of the thin film and wavenumber k = 2D/D in the medium outside the thin film and substrate. The intensity reflection coefficient for specular reflection is obtained as the square of the absolute value of the amplitude reflection coefficient. Equation (7) is periodic in terms of the film thickness D with period
di λ ] = ; . ' , . , „ ■ (8)
where it is assumed that refractive indices
Figure imgf000034_0001
and n2are real. Low reflection of the thin film sample can be separately obtained at the corresponding Brewster angles for two different wavelengths Di and Cfc when equation D =
Figure imgf000034_0002
= md([$), with some small integers m and n, is approximately valid. The reflectance at the Brewster angle for p polarized light is not exactly zero, if n3 contains a nonzero imaginary part.
As a special case a silicon dioxide thin film on silicon substrate in vacuum is considered to be used as an example for an absolute power measurement with a reference to example 2 on the reflection coefficient angular dependence.
In the example, reflectances as a function of angle of incidence were calculated for a detector structure to be utilised for absolute power measurement for monochromatic wavelengths with the indicated thicknesses of the oxide layer. The equations were used for optimization to achieve the maximum EQE at the minimum reflectance. The optimization algorithm was used to drive an adjustment arrangement arranged to adjust the angle of incidence so that the beam meets the detector at Brewster angle.
In the example according to an embodiment for use with multiple wavelengths, a thin film thickness of D = 2908 nm then produces low intensity reflection for p po- larized light at the Brewster angle for wavelengths . . . 488 nm, 529 nm, 576 nm, 633 nm, 703 nm, 790 nm ... This result is useful since frequently used fixed laser wavelengths 488 nm and 633 nm can then be used with low reflection of the same thin film sample. Such a favourable situation can be obtained because c/(488 nm)/d(633 nm) is close to the ratio 10/13. Similar ratios of small integers can be found for other multiplets of convenient laser wavelengths, which allows radiation power measurements at several fixed wavelengths using the same detector with angular adjustment at the desired wavelength.
Example 2, reflectance as a function of angle of incidence at certain wave- lengths
Fig. 1 OA and 1 OB respectively illustrate reflectance as a function of angle of incidence for a 500 nm (Fig 10A) and 800 nm (Fig 10B) photon radiation from a Si diode surface with various indicated oxide layer thicknesses according to the figure. Equations 5-8 shown in example 1 are used in the determinations. The oxide layer thickness is shown at the right hand side down corner in nanometers (nm). The radiation in the example was assumed to be p-polahzed for the indicated radiation. Although a curve appears to meet the zero reflectance, it does not in practice. It is also same way for the minima in the Figs 10B and 10C, too. This is because of non-zero imaginary part of the silicon substrate referactive index.
Fig. 10C demonstrates reflectance as a function of the angle of incidence for a Si diode surface with various indicated oxide layer thicknesses in range of 2900-2916 nm. The figure also helps to understand an embodiment of the invention that uses a larger thickness for the oxide layer for standard fixed laser wavelengths to be used in a detector that has a structure according to an example of Fig. 11 and/or Fig.1.
Example 3
The photon radiation is indicated in Fig. 11 by γ, γl, γ2 and γ3, in several aspects of the detector. The point 104 is the reflection point of the inputted photons at a detector surface part. The portion 105 of radiation is a forward reflected portion γl that can be stronger than the scattered rays 106. In the Fig 11 the layer 301 is silicon dioxide layer, and the pure silicon body is indicated by the numerals 107 and 118. The γ2 illustrates a wave guide mode propagating in the oxide layer. Such wave guide modes can appear into the oxide layer 301 because of scattering from atoms, dislocations and/or other imperfections potentially present in the structure. In order to control the wave guide modes, the detector can in an embodiment of the invention have DBR structure (203) or a reflector (202, 210, and/or 211 ) that reflects the γ2 type photons into such a path that leads them into the pure silicon body 107. A reflector 211 can be formed near the edge by a wedge cavity in the oxide layer. Another kind of reflector can be formed by a dendrite ridge demon- strated by the serrated ridge cross section 210. Several ways of DBR structures are illustrated in Fig 11 for corresponding embodiments indicated in the Fig 11. The DBR structure 202 can comprise a mirror, a detector or both in the structure according to respective embodiments. The DBR structure 203 is a periodic grating that can be present optionally or in addition to the 202. According to an embodi- ment, the layer edges of the layer 301 can be rounded and polished so to reflect photons better back, and thus to the path leading into the pure silicon body 107. The photon γ3 demonstrates a photon with photon energy that converts to electric energy in form of a photocurrent, appearing as the energy that belongs to the pair of electron and hole (e~, h+). The distance of the photon γ3 travelled can be quite long, even several hundreds of micrometers. The detector body thickness can be that of a silicon wafer, in order about 0,5 mm, for the 118 and/or for the part 107 in an appropriate embodiment.
Example 4
A detector structure has been embodied according to Fig. 1. The detector struc- ture has a detector part 118 that has a silicon substrate body made of pure silicon in planar geometry. The detector part 118 is arranged to be adjustable in respect to the entrance aperture for the beam 103 to enter at the Brewster angle in to the detector structure, so enabling to utilize the maximum EQE of the silicon body at the wavelength of the incoming radiation. According to an example of an embodi- ment of the invention the spot 104 is in the center of the spherical part 107. In this example the part 107 is embodied as a mirror with very high reflectance as arranged to focus by reflection the diffuse radiation to a spot on a detector. The spot does not necessarily be exactly the same as the spot 104 in which the diffuse and/or specular reflected beam parts are collected, especially in such an embodi- ment variant in which the part 107 does not move with the detector part 118. In the example, according to an embodiment the opening is arranged so that the opening has a well known area with high accuracy and operates as a collimator part. The reflected parts of the radiation are collected onto the detector part 118.
Example 5.
The detector structure comprises in addition to that shown in example 4 also a mirror at the oxide layer edge, DBR-structure, diffraction grating or a combination thereof so arranged that the modes of the radiation that propagate in the oxide layer in wave guide mode are directed into the silicon body to and/or back to the original direction to utilise the high IQE as much as possible. Example 6.
The set up is similar to that shown in example 4, but differs from that so that the mirror 107 has been replaced by a detector having the oxide layer and a silicon body structure but also the shape of the mirror 107 in example 4, and thus the de- tector is able to focus the reflected radiation as in example 4 back to the detector part 118, but can also operate as detector, so enhancing the EQE. The detector part 107 can be coupled in parallel with the detector part 118. In other words, in example 5, the mirror 107 can act as a secondary detector or a part of the detector, depending on the desire the secondary detector 107 is used in the embodi- ment in question as a separately coupled or in parallel with the detector 118. Fig 4 gives further examples on such embodiments.
Example 7.
In example 7 at least one of the parts 118 and 107 has the detector structure comprising in addition to that shown in example 4 also a mirror at the oxide layer edge, DBR-structure, diffraction grating or a combination thereof so arranged that the modes of the radiation that propagate in the oxide layer in wave guide mode are directed into the silicon body to and/or back to the original direction to utilise the high IQE as much as possible.
Example 8
In example 8 at least one of the parts 118 and 107 is arranged to be tiltable/pivotable in respect to the entering beam 103 from the entrance opening for the beam to meet the detector part 118 in Brewster angle. Because of the aperture system for the entering beam, this means that in embodiments in which the aperture or opening for beam 103 has essentially the same cross section area, the 107 is advantageously moved along to the part 118 for the Brewster angle with the particular wavelength of the radiation beam 103. According to an embodiment the part 118 has locking means arranged to lock the geometry for the Brewster angle for the radiation at the wavelength. According to an embodiment, the part 107 has locking means to lock according to the part 118 for the beam to meet the part 118 at the Brewster angle. According to an embodiment of the invention the detector piece 118 is arranged to be fixed but the 113 is arranged to move in respect to the 111 via a flexible joint 117. However, the movement and/or fixation of the parts 113 and 111 in respect of each other are not limited as such.

Claims

Claims
1. A detector characterized in that the detector (100) comprises:
- at least one film layer (301 ) on a substrate (118) so forming a structure to guide radiation (7,^1,^2,^3), within a wave length in a wavelength range and
- means (107, 202, 203, 210, 211 ) arranged to get at least a certain part (yl,\$2$3\Mi said radiation (γ) absorbed in the detector body (118) for a conversion of the energy of said radiation photons (γ3) to energy of an electrical current (h+, e" ) in an operation temperature (T) of the detector.
2. A detector according to claim 1 comprising in said detector (100) in a plural- ity of film layers at least a film layer on such a substrate that constitute the detector body (107, 301 ), wherein said film layer is arranged to direct a certain portion (γ2, γ3) of radiation (γ) incident to said layer.
3. A detector according to claim 1 comprising in said detector (100) a surface (107, 202, 203, 210, 211 ) arranged into a geometry capable to reflect at least a part of the secondary (71,^2,^3,105, 106) and/or a further portion of said radiation as further reflected into the detector body (118).
4. A detector according to claim 3 wherein said means (107) comprise a surface of the detector (100), which surface is arranged to operate as mirroring surface with the mirroring material characteristic reflectance.
5. A detector according to claim 3, wherein in said detector (100) said means (107) comprise a surface comprising material (301 ,118) of the detector arranged to form a co-detectorDs(107) film layer surface in a mirroring geometry.
6. A detector according to claim 1 comprising in said detector (100) a layer made of material that has an internal quantum efficiency dependent on the tem- perature.
7. A detector according to any one of the previous claims, characterized in that said detector (100, 700) is constituted to comprise at least one of the following: photodiode, photomultiplier tube, trap detector (118,107), thermal detector, and a radiation converter structure arranged to convert radioactivity originating radiation to photons (γ, y\,ϊ^2,φ), arranged for a measurement based on quantum conversion to electric current.
8. A detector comprising in said detector (100) at least one film layer (301 ) in a plurality of film layers (301 , 501 , 502, 601 , 602, 603, 118, 107) in a structure (300, 400, 500, 600) arranged to absorb radiation energy within a wave length range of said radiation, wherein at least one of said layers is arranged to convert said radia- tion to electrical current in an operation temperature of the detector.
9. A detector according to claim 8 comprising in said detector (100, 700) at least one of the following: photodiode, photomultiplier tube, thermal detector, a radiation converter structure arranged to convert radioactive radiation to photons, arranged for a measurement based on quantum conversion to electric current, an ar- ray of at least one of the mentioned .
10. A detector according to any one of the previous claims, wherein said detector (100, 700) has quantum efficiency of 100 % -p%, wherein said p is at least in one of the ranges: 10-1 , 1-0.1 , 1 -0.001 , 0.01-0.0001 , 0.001 -0.000001 , 0.000001- 0.000000001 and an intermediate range comprising a lower value for said range end from one of said ranges and a higher value for said range end from one of said ranges from another range being exclusive to said range from which the lower value was taken.
11. A measuring method of radiation power comprising in said method (900):
- adjusting optical path of said radiation having a wavelength for a minimum reflectance of the incident portion of the radiation by adjusting said optical path to meet the angle of incidence at the Brewster angle,
- exposing a radiation detector, which comprises a film layer part, to an incident part of said radiation to get absorbed for use in quantum energy con- version,
- controlling the detectorDs operatincjemperature in an operation temperature range,
- converting energy of the radiation photons to energy in form of electron current.
12. The measuring method according to claim 11 , wherein the method (900) comprises a phase of exposing in addition to said film layer part of the detector also a second film layer part of the detector part to a secondary part of the radiation.
13. The measuring method according to claim 11 , wherein in the method (900), said incoming angle, as defined in respect to the normal of the surface on the film layer, is larger than Brewster angle of incoming radiation.
14. The measuring method according to claim 11 , wherein in the method (900), said incoming angle, as defined in respect to the normal of the surface on the film layer, is smaller than Brewster angle of incoming radiation.
15. The measuring method according to claim 11 , wherein in the method (900), said incoming angle, as defined in respect to the normal of the surface on the film layer, is equal to Brewster angle of incoming radiation.
16. The measuring method according to claim 11 , wherein the method (900) comprises a phase of determining a quantum efficiency (EQE) for a said film layer part and/or an efficiency (IQE) for defining the ratio of converting energy of a radiation photons to electron current in an operation temperature for radiation in a wave range having wave range minimum and maximum wavelength and the respective energies.
17. The measuring method according to claim 11 , wherein the method (900) comprises a phase of determining quantum efficiency via at least one of the following quantity for the detector in at least one operation temperature: impedance, resistance, capacitance, conductivity, a current carrier mobility, electrostatic polari- zation of a structural unit, and polarizability according to the electric field of the radiation.
18. The measuring method according to claim 11 , wherein the method (900) comprises a phase of averaging, to be made for obtaining an average which is at least one of the following: arithmetic, geometric, harmonic, said average made ac- cording to as a gliding average or as an average of fixed interval during the data sampling.
19. The measuring method according to claim 11 , wherein in the method (900) said radiation originates to at least one radiation source which is arranged to pro- duce radiation having a wave length in range which wave length is at least one of the following:
- wavelength between a radio wavelength and an infrared wavelength,
- wavelength in infrared,
- wavelength of visible light, - wavelength of ultraviolet,
- wave length of X-rays, and
- an intermediate wavelength of two successive above mentioned wavelengths.
20. The measuring method according to claim 11 , wherein in the method (900) said radiation comprises a first feature and/or a second feature, which first and/or second feature is at least one of the following:
- (i) the wavelength characteristic to the radiation source,
- (ii) on-duty pulse length, - (iii) length of off-duty period between two successive pulses,
- (iv) repetition rate of the on-duty occurrences,
- (v) radiation intensity,
- (vi) energy and/or power per pulse,
- (vii) polarization of the radiation, - (viii) radiation has a DC-component of the power between a first moment and a second moment that are between the radiation source turn on and off, and
- a combination of at least two or more of the features (i)-(viii).
21. A measuring arrangement comprising a detector (700) according to a claim 1 -10.
22. A measuring arrangement according to claim 21 , wherein the measuring arrangement (700) comprises an optical path for the incident radiation to be directed on to the detector.
23. A measuring arrangement according to claim 21 , wherein the measuring arrangement (700, 800) comprises a cooling means arranged to cool at least a part of said detector to be operable in an operating temperature.
24. A measuring arrangement according to claim 23, wherein the measuring arrangement (700, 800) comprises cooling means that comprises at least one of the following: a cold finger as such, cooling means that is based on a circulation of a coolant, evaporation based cooling means, a heat exchanger, a peltier element, magnetic cooling means arranged to bind energy into a magnetic field and a laser- cooling means.
25. A measuring arrangement according to claim 24, wherein the measuring arrangement (700) comprises as said coolant nitrogen in liquid form.
26. A measuring arrangement according to claim 24, wherein the measuring arrangement (700) comprises as said coolant that comprises magnetic properties.
27. A measuring arrangement according to claim 24, wherein the measuring arrangement (700) comprises material with said magnetic properties as ferromag- netic properties or paramagnetic properties.
28. A measuring arrangement according to claim 22, wherein the measuring arrangement (100, 700) comprises such said optical path that comprises a vacuum part.
29. A measuring arrangement according to claim 22, wherein the measuring ar- rangement (100, 700) comprises in said optical path a wave guide part (118) that is other than vacuum.
30. A measuring arrangement according to claim 22, wherein the measuring arrangement (100, 700) in said optical path comprises said detector.
31. A power meter arranged to measure radiation power comprising a measur- ing arrangement according to claim 22 as arranged into a device as said power meter (800).
32. A measuring system comprising in said system (800) at least a first measuring arrangement (700) according to claim 21 and/or a first power meter according to claim 31 and a second measuring arrangement (700) according to claim 21 and/or a second power meter according to claim 31 , arranged to co-operate for a measurement of radiation power.
33. A measuring system according to claim 31 , wherein in said system (800) said co-operation is arranged to be redundant in respect along a radiation feature in claim 20.
34. A measuring system according to claim 32, wherein in said system (800) said co-operation is arranged to be at least partly non-overlapping along a radiation feature in claim 19.
35. A photodiode comprising a detector (100) according to any one of claims 1 - 10.
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EP2160766A4 (en) 2014-06-11
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EP2160766A1 (en) 2010-03-10
FI20070429A0 (en) 2007-05-31

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