WO2020178176A1 - Optoelectronic semiconductor light source and bragg mirror - Google Patents

Optoelectronic semiconductor light source and bragg mirror Download PDF

Info

Publication number
WO2020178176A1
WO2020178176A1 PCT/EP2020/055295 EP2020055295W WO2020178176A1 WO 2020178176 A1 WO2020178176 A1 WO 2020178176A1 EP 2020055295 W EP2020055295 W EP 2020055295W WO 2020178176 A1 WO2020178176 A1 WO 2020178176A1
Authority
WO
WIPO (PCT)
Prior art keywords
bragg mirror
light source
optoelectronic semiconductor
radiation
semiconductor light
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/EP2020/055295
Other languages
French (fr)
Inventor
Alan Lenef
David KLOTZKIN
Xin Wen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ams Osram International GmbH
Research Foundation of the State University of New York
Original Assignee
Osram Opto Semiconductors GmbH
Research Foundation of the State University of New York
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 Osram Opto Semiconductors GmbH, Research Foundation of the State University of New York filed Critical Osram Opto Semiconductors GmbH
Priority to DE112020001069.4T priority Critical patent/DE112020001069B4/en
Publication of WO2020178176A1 publication Critical patent/WO2020178176A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/60—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
    • F21K9/68—Details of reflectors forming part of the light source
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/60—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
    • F21K9/64—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction using wavelength conversion means distinct or spaced from the light-generating element, e.g. a remote phosphor layer
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V7/00—Reflectors for light sources
    • F21V7/22—Reflectors for light sources characterised by materials, surface treatments or coatings, e.g. dichroic reflectors
    • F21V7/24—Reflectors for light sources characterised by materials, surface treatments or coatings, e.g. dichroic reflectors characterised by the material
    • F21V7/26—Reflectors for light sources characterised by materials, surface treatments or coatings, e.g. dichroic reflectors characterised by the material the material comprising photoluminescent substances
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G02B5/0816—Multilayer mirrors, i.e. having two or more reflecting layers
    • G02B5/0825—Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only
    • G02B5/0833—Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only comprising inorganic materials only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
    • G02B5/3066—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state involving the reflection of light at a particular angle of incidence, e.g. Brewster's angle
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/14—Details
    • G03B21/20—Lamp housings
    • G03B21/2006—Lamp housings characterised by the light source
    • G03B21/2033—LED or laser light sources
    • G03B21/204—LED or laser light sources using secondary light emission, e.g. luminescence or fluorescence
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0087—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for illuminating phosphorescent or fluorescent materials, e.g. using optical arrangements specifically adapted for guiding or shaping laser beams illuminating these materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/022—Mountings; Housings
    • H01S5/023—Mount members, e.g. sub-mount members
    • H01S5/02325—Mechanically integrated components on mount members or optical micro-benches
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
    • H10F39/80—Constructional details of image sensors
    • H10F39/806—Optical elements or arrangements associated with the image sensors
    • H10F39/8067—Reflectors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/84—Coatings, e.g. passivation layers or antireflective coatings
    • H10H20/841—Reflective coatings, e.g. dielectric Bragg reflectors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/8506—Containers
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/851—Wavelength conversion means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/851—Wavelength conversion means
    • H10H20/8511—Wavelength conversion means characterised by their material, e.g. binder
    • H10H20/8512—Wavelength conversion materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/851—Wavelength conversion means
    • H10H20/8515—Wavelength conversion means not being in contact with the bodies
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/855—Optical field-shaping means, e.g. lenses
    • H10H20/856—Reflecting means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
    • H10K59/30—Devices specially adapted for multicolour light emission
    • H10K59/38—Devices specially adapted for multicolour light emission comprising colour filters or colour changing media [CCM]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/30—Semiconductor lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0078—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for frequency filtering

Definitions

  • An optoelectronic semiconductor light source is provided. Further, a Bragg mirror for an optoelectronic semiconductor light source is provided.
  • An object to be achieved is to provide a Bragg mirror for an optoelectronic semiconductor light source improving light- extraction efficiency.
  • the optoelectronic semiconductor light source comprises one or a plurality of semiconductor chips.
  • the at least one semiconductor chip is configured to emit primary radiation. If there is a plurality of semiconductor chips, all semiconductor chips could emit primary radiation of the same spectral properties or there could be semiconductor chips emitting with different peak wavelengths, for example.
  • the optoelectronic semiconductor light source comprises one or a plurality of Bragg mirrors.
  • the at least one Bragg mirror is composed of a plurality of reflective layers.
  • the reflectivity of the Bragg mirror and, thus, of the reflective layers is preferably based on interference.
  • the reflective layers can be of transmissive, transparent materials.
  • the Bragg mirror is preferably electrically insulating; however, as an
  • the Bragg mirror could also be electrically conductive .
  • the optoelectronic semiconductor light source comprises one or a plurality of luminescence conversion elements.
  • the luminescence conversion element is configured to convert part or all of the primary radiation into secondary radiation.
  • the secondary radiation has a longer wavelength than the primary radiation.
  • the luminescence conversion element comprises one or a plurality of phosphors.
  • the phosphor is an inorganic material, especially a ceramic.
  • the phosphor is an inorganic material, especially a ceramic.
  • phosphor can also be selected from an organic material.
  • quantum dots might be used as the phosphor.
  • the phosphor is at least one of the following luminescent materials: Eu 2+ -doped nitrides such as
  • luminescent materials such as ( Sr, Ba, Ca) 5 ( PO4 ) 3CI : Eu ⁇ 1 ; KSF luminescent materials such as K ⁇ SiFgiMn ⁇ 1 .
  • the Bragg mirror is arranged between the semiconductor chip and the luminescence conversion element. This means in particular that primary radiation can reach the luminescence conversion element only after running through the Bragg mirror.
  • One or both of the luminescence conversion element and of the semiconductor chip can be arranged distant from the Bragg mirror. Otherwise, the luminescence conversion element and/or the semiconductor chip can touch the Bragg mirror.
  • the Bragg mirror is reflective for the secondary radiation and is transmissive for the primary radiation.
  • the term 'reflective' particularly refers to a reflectivity of at least 80% or 90% or 95% or 98%.
  • the term 'transmissive' may refer to a transmittance of at least 80% or 90% or 95% or 98%.
  • the respective numerical values may refer to an overall photometric power of the primary radiation and the secondary radiation, respectively, incident on the Bragg mirror.
  • the Bragg mirror comprises reflector layers of at least three different materials.
  • the different materials have different refractive indices. This means that the Bragg mirror comprises a
  • the Bragg mirror comprises at least two different kinds of layer pairs.
  • Each kind of layer pair is made up of reflective layers of two different materials. This means, for example, that a first kind of layer pairs comprises at least some of the reflector layers of the first material and at least some of the
  • a second kind of layer pairs may comprise at least some of the reflector layers of the second material or of the fourth material and at least some of the reflector layers of the third material.
  • the different kinds of layer pairs have different Brewster angles for p-polarized radiation, in particular for p-polarized secondary radiation.
  • the primary radiation impinges on the Bragg mirror in either s or p polarization, some combination, or random
  • the optoelectronic semiconductor light source comprises a semiconductor chip configured to emit primary radiation, a Bragg mirror, and a luminescence conversion element configured to convert at least part of the primary radiation into secondary radiation having a longer wavelength.
  • the Bragg mirror is arranged between the
  • the Bragg mirror comprises reflector layers of at least three different materials with different refractive indices, so that at least two different kinds of layer pairs are formed, each kind of layer pairs being made up of reflective layers of two
  • the different kinds of layer pairs have different Brewster angles for p-polarized radiation.
  • each kind of layer pair of two specific materials as used in a Bragg mirror has a specific Brewster angle.
  • the reflectivity of the respective kind of layer pairs is significantly reduced and may be virtually zero for p polarized light. This means that at the Brewster angle a comparably large portion of the secondary radiation may leak through the Bragg mirror.
  • optoelectronic semiconductor light source can be increased.
  • the Brewster angles of the different kinds of layer pairs differ by at least 0.5° or by at least 1° or by at least 1.5° or by at least 2°.
  • said difference is at least 2.5°. If there are more than two different kinds of layer pairs, this can be true pairwise.
  • At the Brewster angle of one of the different kinds of layer pairs at least one other kind of layer pairs or all other kinds of layers pairs together has/have a reflectivity for the secondary radiation of at least 20% or of at least 40% or of at least 60% or of at least 80%, in particular for p-polarized radiation.
  • a reflectivity for the secondary radiation of at least 20% or of at least 40% or of at least 60% or of at least 80%, in particular for p-polarized radiation.
  • a reflectivity of the Bragg mirror is at most 2% in the wavelength range of the primary radiation.
  • the term 'wavelength range of the primary radiation' refers in particular to that spectral range in which an intensity of the primary radiation is at least 5% or at least 2% of a peak intensity of the primary radiation.
  • a reflectivity or an average reflectivity of the Bragg mirror in the wavelength range of the secondary radiation is at least 80% or at least 90% or at least 95% or at least 98%.
  • the term 'wavelength range of the secondary radiation' refers in particular to that spectral range in which an intensity of the secondary radiation is at least 10% or at least 5% of a peak intensity of the secondary
  • the Bragg mirror is configured for high transmission of the primary radiation for angles of incidence of up to at least 30° or of up to at least 40° or of up to at least 50° or of up to at least 60°.
  • angles of incidence of up to at least 30° or of up to at least 40° or of up to at least 50° or of up to at least 60°.
  • transmittance of the Bragg mirror for the primary radiation is at all angles at least 90% or at least 95% or at least 98%.
  • the blueshift of the primary wavelength passband of the Bragg mirror will generally limit the angle of the incoming primary radiation.
  • LRP laser activated remote phosphor
  • the Bragg mirror is configured for high reflectivity of the secondary radiation for angles of incidence of up to at least 65°.
  • the reflectivity of the Bragg mirror for the secondary radiation is at all angles at least 80% or at least 90% or at least 95%.
  • the Bragg mirror comprises exactly two different kinds of layer pairs.
  • the Bragg mirror preferably comprises exactly three different materials for the reflective layers.
  • the Bragg mirror comprises exactly three different kinds of layer pairs.
  • the Bragg mirror comprises exactly four different materials for the reflective layers.
  • the Bragg mirror comprises at least 3 or at least 4 or at least 5 layer pairs inclusive. This can be true for one or for some or for all kinds of layer pairs.
  • the number of layer pairs per kind of layer pairs is at most 40 or at most 30 or at most 20.
  • the number of layer pairs per kind of layer pairs is between 4 and 18 inclusive. This configuration enables cost-efficient manufacturing.
  • the secondary radiation has a spectral width of at least 60 nm or of at least 80 nm or of at least 100 nm.
  • the spectral width is at most 150 nm or at most 120 nm or at most 100 nm.
  • the secondary radiation can be broadband radiation .
  • the primary radiation has a spectral width of at most 40 nm or of at most 30 nm or of at most 15 nm or of at most 5 nm.
  • said spectral width is at least 1 nm or at least 5 nm.
  • 'spectral width' may refer to a full width at half maximum, FWHM for short. Or it may also refer to a standard deviation in the case of Gaussian-like-shaped spectra.
  • thicknesses of the reflective layers of at least one of the materials vary by at least 10% or by at least 20% or by at least 30% of a maximum thickness of the respective reflective layers within said kind of layer pairs.
  • a variation of 20% for example, means that there is at least one reflective layer with a thickness of at most 80% of the respective maximum thickness. This means that the thicknesses of the reflective layers vary significantly. This variation applies preferably to all kinds of reflective layers.
  • the reflective layers have constant thicknesses in each case.
  • the reflective layer can be of planar fashion, but curved reflective layers are possible in principle, too.
  • the thickness is measured in a direction perpendicular to a main face of the respective reflective layer.
  • the different kinds of layer pairs are arranged block by block.
  • the different kinds of layer pairs are not intermixed with each other. It is possible that the blocks directly follow one another.
  • At least 90% of the reflective layers have a thickness of at least 0.20 L/n or at least 0.22 L/n or at least 0.24 L/n.
  • at least 90% of the reflective layers have a thickness of at most 0.49 L/n or of at most 0.45 L/n or of at most 0.41 L/n.
  • n is the refractive index, in particular at 300 K
  • L is the wavelength of maximum intensity for the resepective radiation to be considered, that is, the wavelength of maximum intensity for the primary radiation to be transmitted and the wavelength of maximum intensity for the secondary radiation to be reflected; otherwise, L could be a fix wavelength like 500 nm.
  • the thickness of at least 10% or of at least 20% or of at least 40% or of at least 50% or of at least 70% of the reflective layers is at least 0.28 L/n .
  • the thicknesses mentioned in the previous two paragraphs can be true for all of the reflective layers or only for some kinds of reflective layers, that is for example only for the reflective layers of the first and of the second material, or only for the reflective layers of some of the blocks of layer pairs .
  • the optoelectronic semiconductor light source comprises a transmissive carrier.
  • the Bragg mirror is mounted onto the carrier.
  • the carrier is of sapphire or of a glass.
  • the at least one semiconductor chip is a laser diode chip.
  • the primary radiation is coherent radiation.
  • the carrier is located between the semiconductor chip and the Bragg mirror. Hence, the primary radiation runs through the carrier prior to reaching the Bragg mirror.
  • the primary radiation travels through a gas or through an evacuated area prior to reaching the carrier and/or the Bragg mirror. This means that a light-exit surface of the semiconductor chip then does not touch the carrier and/or the Bragg mirror. It is possible that an optical element is arranged between the semiconductor chip on the one hand and the carrier and/or the Bragg mirror on the other hand. By means of such an optical element, the primary radiation can be focused onto the luminescence conversion element.
  • a light-exit surface of the luminescence conversion element is small.
  • the size of the light-exit surface is at most 1 mm ⁇ or
  • the light- exit surface is the only surface from which the secondary radiation, and as an option the primary radiation, is emitted from the luminescence conversion element, the carrier and the Bragg mirror.
  • the optoelectronic semiconductor light source further comprises an adhesive.
  • the adhesive comprises or consists of a polymer like a silicone and/or of a glass like a so-called low-temperature glass with a softening temperature of at most 350 °C.
  • the adhesive may be filled with a filler like glass particles or metal oxide particles to adjust the refractive index, a coefficient of thermal expansion and/or a thermal conductivity.
  • the semiconductor chip can be attached to the Bragg mirror, or the Bragg mirror can be attached to the carrier, or the luminescence conversion element can be attached to the carrier and/or the Bragg mirror.
  • the light source comprises more than one adhesive.
  • the adhesive is an optical adhesive, that is, the primary radiation and/or the secondary radiation has/have to pass the at least one adhesive prior to leaving the light source. For example, the primary radiation runs through the adhesive prior to reaching the Bragg mirror.
  • the at least one semiconductor chip is a light-emitting diode chip.
  • the primary radiation is incoherent radiation.
  • the adhesive has a low refractive index, in particular of at most 1.41 or of at most 1.45 or of at most 1.48 or of at most 1.55. This can be true at a wavelength of 500 nm and at a temperature of 300 K.
  • the adhesive has a high refractive index of at least 1.65 or of at least 1.8.
  • the above-mentioned refractive indices may refer to a
  • the adhesive is thin.
  • a thickness of the adhesive is preferably at least 0.2 pm or at least 0.5 pm.
  • the thickness of the adhesive is at most 2 pm or at most 4 pm or at most 10 pm.
  • the Bragg mirror can be directly deposited on to the semiconductor light source or luminescent conversion element via a number of methods known in the art, including physical vapor deposition, chemical vapor
  • the Bragg mirror forms a cage all around the luminescence conversion element except for the light-exit side of the luminescence conversion element.
  • the luminescence conversion element is of prismatic shape and the Bragg mirror covers five of six sides of said cuboid.
  • the luminescence conversion element is a ceramic body, in particular a ceramic platelet.
  • the luminescence conversion element can be highly thermally conductive.
  • the luminescence conversion element can be of plane-parallel shape. Seen in top view onto the light-exit side, the luminescence conversion element may be rectangular or hexagonal or circular.
  • the secondary radiation is green light and/or yellow light and/or orange light and/or red light.
  • the primary radiation is blue light and/or cyan-colored light and/or near-ultraviolet radiation. Near-ultraviolet radiation particularly refers to peak wavelengths of at least 340 nm and of at most 405 nm. When combining blue primary radiation and green/yellow/orange secondary radiation, white light may be emitted by the light source.
  • the reflector layers are of metal oxides or semiconductor oxides. Binary as well as ternary or quaternary oxides can be used. For example, the materials of the reflector layers are selected from the following group: SiOg, TagOg, MgFg, ITO, ZnO, CaFg, BaFg,
  • a Bragg mirror for an optoelectronic semiconductor light source is provided.
  • the Bragg mirror is configured like the Bragg mirror of the optoelectronic semiconductor light source as explained in conjunction with the exemplary embodiments described above.
  • features for the Bragg mirror are also disclosed for the optoelectronic semiconductor light source and vice versa.
  • the Bragg mirror comprises a plurality of reflector layers of at least three different materials with different refractive indices
  • each kind of layer pairs being made up of reflective layers of two
  • the Bragg mirror is reflective for at least one of green, yellow, orange and red light and is transmissive for at least one of blue light, cyan-colored light and near-ultraviolet radiation.
  • the different kinds of layer pairs have different Brewster angles for p-polarized radiation .
  • the Bragg mirror and the optoelectronic semiconductor light source described herein are used, for example, in head lamps for vehicles like cars, in spot lights, in stage lighting, or in medical applications like endoscopes or curing substances. Further, applications in the field of spectroscopy are also possible .
  • An optoelectronic semiconductor light source and a Bragg mirror described herein are explained in greater detail below by means of exemplary embodiments with reference to the drawings. Elements which are the same in the individual figures are indicated with the same reference numerals. The relationships between the elements are not shown to scale, however, but rather individual elements may be shown
  • Figures 1, 3 and 5 show schematic sectional representations of exemplary embodiments of an optoelectronic semiconductor light source described herein,
  • Figure 2 shows a schematic sectional representation of an exemplary embodiment of a Bragg mirror for optoelectronic semiconductor light sources described herein,
  • Figure 4 shows a schematic perspective representation of an exemplary embodiment of an optoelectronic semiconductor light source described herein
  • Figures 6 and 7 show schematic tabular representations of exemplary embodiments of Bragg mirrors for optoelectronic semiconductor light sources described herein,
  • Figure 8 shows a representation of reflectivity of p- polarized radiation for a two material Bragg mirror with the corresponding Brewster angle region, used in a configuration such as in Figure 1,
  • Figure 9 shows a representation of a reflectivity of an
  • Figure 10 shows a representation of a reflectivity of a two material Bragg mirror for comparison to the
  • LARP Laser Activated Remote Phosphor
  • transmissive LARP system 1 is shown in the exemplary embodiment of Figure 1.
  • a focused pump beam of primary radiation P preferably generated by one or more
  • the semiconductor chips 2 which are realized as blue laser diodes, for example, is incident on a luminescence conversion element 3, which is bonded to a transparent substrate 6 by means of an adhesive 7.
  • the carrier 6 is of a material of high thermal conductivity, for example of sapphire .
  • the small luminescent region pumped by the laser radiation P from the semiconductor chip 2 emits secondary radiation S in both forward and backward (towards the pump) directions.
  • a dichroic Bragg mirror 4 is used to redirect the backwards emitted luminescence into the desired forward direction. Without such a dichroic Bragg mirror 4, around half of the luminescence of the secondary radiation S would go back towards the semiconductor chip 2, resulting in low overall conversion efficiency. It is also advantageous to avoid having secondary radiation S or even scattered pump light P in the carrier 6. Otherwise, the light P, S will spread laterally beyond the desired small area luminescent region, thus increasing etendue. This will degrade the desired high luminance emission.
  • the luminescent region of the light source 1 is limited to a light-exit side 30 of the luminescence conversion element 3.
  • the light generated within the luminescence conversion element 3 should also escape the total internal reflection (TIR) condition at the emitting surface 30 because the converter material usually has a relatively high refractive index compared to the output medium which is usually air.
  • TIR total internal reflection
  • This extraction problem is usually mitigated by introducing optimized volume and/or surface scattering to couple the TIR modes into the extractable output modes.
  • the dichroic Bragg mirror 4 is in fact part of the light extraction solution.
  • these TIR effects at surfaces and additional scattering needed for light extraction create relatively strong cavity effects within the luminescence conversion element 3, which enhance any small amount of blue or converted light transmission through the dichroic Bragg mirror 4.
  • the dichroic Bragg mirror 4 "sees" multiple ray bounces from the light within the luminescence conversion element 3, amplifying the loss effects which occur from the non-ideal reflecting characteristics of a real dichroic .
  • the dichroic Bragg mirror 4 should also transmit the partially collimated shorter wavelength pump light P, to maximize coupling of pump light P into the luminescence conversion element 3.
  • the Bragg mirror 4 comprises first reflector layers 41 of a first material, second reflector layers 42 of a second material, third reflector layers 43 of a third
  • the first an second layers 41, 42 are grouped to layer pairs 51 of a first kind, the third an fourth layers 43, 44 are grouped to layer pairs 52 of a second kind.
  • All the first layer pairs 51 are arranged in a first block 91, and the second layer pairs 52 are arranged in a second block 92.
  • the blocks 91, 92 are arranged directly on top of one another.
  • All layers 41, 42, 43, 44 are of constant thickness. The thickness of the layers 41, 42, 43, 44 is around or slightly above l/4 wherein l is in particular a peak wavelength of the secondary radiation S.
  • the Bragg mirror 4 can comprise a bottom layer 45 and/or a cap layer 46.
  • the layers 45, 46 can be of the same or of different materials as/than the layers 41, 42, 43, 44.
  • the layers 45, 46 can serve as protective layers or as coupling layers.
  • multiple pairs of one set of Bragg materials are followed by multiple pairs onf a second set of Bragg materials.
  • the different pairs of materials are interleaved. It is also possible that different layer pairs could be alternated next to each other.
  • FIG. 3 One such example is shown in Figure 3, where the luminescence conversion element 3 is used with an LED chip 2 for either white light (partial transmission of the short wavelength LED light through the luminescence conversion element 3) or full conversion, where the LED pump light P is fully absorbed by the luminescence conversion element 3.
  • the dichroic Bragg mirror 4 functions to enhance the back-reflection of the longer wavelength
  • the Bragg mirror 4 also decouples the backward directed converted light from the LED 2, making the efficacy of the device 1 less sensitive to the LED chip 2 structure.
  • the Bragg mirror 4 can be applied directly to a ceramic platelet that constitutes the luminescence conversion element 3.
  • the adhesive 7, for example a thin layer of a silicone glue, is located between a radiation main side 20 of the semiconductor chip 2 and the Bragg mirror 4.
  • the luminescence conversion element 3 may be a high thermal conductivity material such as a ceramic YAG:Ce which fully absorbs the pump light P from the bonded LED chips 2 and emits longer wavelength light through only one emission surface 30.
  • the luminescence conversion element 3 is a cuboid, for example.
  • the LED chips 2 can be located on more than one side surface, other than shown in Figure 4.
  • a plurality of LED chips 2 are located on two opposing side surfaces and/or on a back surface and/or on top and bottom surfaces.
  • the light- exit side 30 may be one of the smallest side surfaces of the luminescence conversion element 3. All sides of the
  • luminescence conversion element 3 except for the light-exit side 30 are coated with the Bragg mirror 4. It is possible that the respective surfaces are covered with the LED chips 2 by at least 50% or 70%.
  • the luminescence conversion element 3 becomes narrower in the direction away from the semiconductor chip 2.
  • the luminescence conversion element 3 can completely cover the semiconductor chip 2. All surfaces of the
  • luminescence conversion element 3 are coated with the Bragg mirror 4 except for the light-exit side 30. Such a configuration with a narrowing luminescence conversion element 3 can be used in all other exemplary embodiments, too. There can be more than one semiconductor chip 2 at the bottom side of the luminescence conversion element 3.
  • the entire ceramic phosphor 3 is coated with a very high reflective material, that is the Bragg mirror 4, on all surfaces except for the desired emitting surface 30.
  • the semiconductor chips 2 themselves can serve as reflectors, but a masked dielectric 4 will be required on all other regions of the ceramic phosphor 3 except for the emitting side.
  • the masking step can be eliminated by using a high reflective dichroic coating 4 that allows passage of the blue pump light P. This requires the blue pass region to function over a large angular range. Note that in the case of using a masking step, one could also use an enhanced metallic coating for wide angular range reflection; however, metallic coatings are always lossy and therefore would limit the efficiency of the device 1.
  • the secondary light S is incoherent, it consists of equal fractions of s- and p- polarized waves.
  • a unique feature of this coating 4 is that it ideally has omnidirectional reflection of the longer wavelength light S, while having very high transmission for the short wavelength light P over at least a limited angular range. In cases where LED pumping is used, the transmission of the short wavelength light P must also be omnidirectional.
  • the problem of designing and fabricating a short wavelength transmitting layer and a longer wavelength reflecting layer for a transmissive LARP configuration such as shown in Figure 1 was solved by using a two-material dielectric stack based on low and high refractive index materials.
  • the low index material could be SiOg and the high index material could be TagOg.
  • the bonding material could be a glass which requires high-temperature bonding.
  • the dichroic stack consists of 40-60 layers, for example, which provide a compromise between high omnidirectional
  • Figure 8 shows a typical simulated reflectance plot for the dichroic/glass bonding layer in the transmissive LARP configuration shown in Figure 1.
  • the pump light P is located.
  • Kx sin qrr where qrr is the angle of incidence on the combined adhesive layer 7 - dichroic 4 for light rays generated within the phosphor 3.
  • the results show how reflectivity varies with both wavelength and angle of incidence from the phosphor to the bonding - dichroic stack, for p-polarized light.
  • the Brewster effect is quite clear in region A, showing a reflection minimum near 0% with K x 3 ⁇ 4 0.6 to 0.7.
  • the Brewster angle q B rr for the stack, as seen by the phosphor, can be determined by the equation:
  • ng and ng are the refractive indices for the two different dielectric stack materials.
  • the symbol npp denotes the refractive index of the phosphor 3.
  • n su p is the refractive index of the carrier.
  • SSL sources such as the LARP
  • the advantage of the Bragg mirror 4 described herein can be expressed by calculating the photon-to-photon conversion factor, comparing a conventional single Bragg stack design to a multiple material pair, Bragg stack design.
  • This conversion factor is the merit function which is used by the algorithms which design the details of the coatings. It is a number between zero and one, which represents the fraction of input photons which are not converted to secondary light coupled out at the front surface 30.
  • a merit function (metric value) of 0.2 implies 80% of input photons are converted to output photons exiting from the target facet in Figure 1.
  • the list below shows results from a benchmark design, with two materials, compared with a three-material design of the same total number of layers (that is, 60 layers) but designed using both pairs of materials to cover the Brewster window.
  • qr is the Brewster angle in the incident medium 1.
  • the Brewster angle for Bragg pairs of SiOg/TagC>5 is 56° degrees, and for MgFg/TagOg it is 57.4°.
  • a dichroic filter constructed, for example, by only Bragg pairs of SiOg/TagC>5, regardless of the details of the design, will have a Brewster window at that angle, and p-polarized light will escape.
  • a dichroic constructed with two sets of disparate materials SiOg/TagC>5 and, for example, indium tin oxide (ITO) (refractive index 1.858) and MgFg (refractive index 1.385)
  • ITO indium tin oxide
  • MgFg reffractive index 1.385
  • the two Brewster angles have to be sufficiently different so that one pair of materials provides reflectivity at the others Brewster window .
  • the dichroic is constructed of Bragg pairs of SiOg/TagOg
  • MgFg/TagOg show that bottom overall transmittance is much higher for the single set of Bragg pairs. As the Brewster window for one pair is compensated by the reflectivity of the half-dichroic stack formed by the other pair, the overall structure has a much improved overall reflectivity.
  • the phosphor is a garnet like YAG, for example.
  • These dielectric layers are fabricated similarly to

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical & Material Sciences (AREA)
  • Multimedia (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Semiconductor Lasers (AREA)

Abstract

In one embodiment, the optoelectronic semiconductor light source (1) comprises a semiconductor chip (2) configured to emit primary radiation (P), a Bragg mirror (4), and a luminescence conversion element (3) configured to convert at least part of the primary radiation (P) into secondary radiation (S) having a longer wavelength. The Bragg mirror (4) is arranged between the semiconductor chip (2) and the luminescence conversion element (3) and is reflective for the secondary radiation (S) and transmissive for the primary radiation (P). The Bragg mirror (4) comprises reflector layers (41, 42, 43, 44) of at least three different materials with different refractive indices, so that at least two different kinds of layer pairs (51, 52, 53) are formed, each kind of layer pairs (51, 52, 53) being made up of reflective layers (41, 42, 43, 44) of two different materials. The different kinds of layer pairs (51, 52, 53) have different Brewster angles for p-polarized radiation.

Description

Description
OPTOELECTRONIC SEMICONDUCTOR LIGHT SOURCE AND BRAGG MIRROR
An optoelectronic semiconductor light source is provided. Further, a Bragg mirror for an optoelectronic semiconductor light source is provided.
An object to be achieved is to provide a Bragg mirror for an optoelectronic semiconductor light source improving light- extraction efficiency.
This object is achieved, inter alia, by an optoelectronic semiconductor light source and by a Bragg mirror as specified in the independent patent claims. Further preferred
developments constitute the subject-matter of the dependent patent claims.
According to at least one embodiment, the optoelectronic semiconductor light source comprises one or a plurality of semiconductor chips. The at least one semiconductor chip is configured to emit primary radiation. If there is a plurality of semiconductor chips, all semiconductor chips could emit primary radiation of the same spectral properties or there could be semiconductor chips emitting with different peak wavelengths, for example.
According to at least one embodiment, the optoelectronic semiconductor light source comprises one or a plurality of Bragg mirrors. The at least one Bragg mirror is composed of a plurality of reflective layers. The reflectivity of the Bragg mirror and, thus, of the reflective layers is preferably based on interference. Thus, the reflective layers can be of transmissive, transparent materials. The Bragg mirror is preferably electrically insulating; however, as an
alternative, the Bragg mirror could also be electrically conductive .
According to at least one embodiment, the optoelectronic semiconductor light source comprises one or a plurality of luminescence conversion elements. The at least one
luminescence conversion element is configured to convert part or all of the primary radiation into secondary radiation. Preferably, the secondary radiation has a longer wavelength than the primary radiation. The luminescence conversion element comprises one or a plurality of phosphors. In
particular, the phosphor is an inorganic material, especially a ceramic. However, in addition or alternatively, the
phosphor can also be selected from an organic material.
Further, quantum dots might be used as the phosphor.
For example, the phosphor is at least one of the following luminescent materials: Eu2+-doped nitrides such as
(Ca, Sr) AlSiN3 : Eu2+, Sr (Ca, Sr) Si2Al2N6 : Eu2+ ,
Figure imgf000004_0001
(Sr,Ca) [L1AI3N4] :EU2+; garnets from the general system
(Gd, Lu, Tb, Y) 3 (Al, Ga, D) 5 (0, X) 12 : RE with X = halide, N or divalent element, D = tri- or tetravalent element and RE = rare earth metals such as LU3 (Ali_xGax) 5033 : Ce2+,
Y3 (Al2-xGax) 5q22 : Ce2+ ; Eu2+-doped SiONs such as
(Ba, Sr, Ca) Si202N2 : Eu2+ ; SiAlONs for instance from the system LixMyLnzSi22_ (m+n) Al (m+n) OnN2 g_n; nitrido-orthosilicates such as AE2-x-aRExEuaSi04_xNx, AE2-x-aRExEuaSi]__y04_x-2yNx with RE = rare earth metal and AE = alkaline earth metal; orthosilicates such as SCAP
luminescent materials such as ( Sr, Ba, Ca) 5 ( PO4 ) 3CI : Eu^1 ; KSF luminescent materials such as K^SiFgiMn^1.
According to at least one embodiment, the Bragg mirror is arranged between the semiconductor chip and the luminescence conversion element. This means in particular that primary radiation can reach the luminescence conversion element only after running through the Bragg mirror. One or both of the luminescence conversion element and of the semiconductor chip can be arranged distant from the Bragg mirror. Otherwise, the luminescence conversion element and/or the semiconductor chip can touch the Bragg mirror.
According to at least one embodiment, the Bragg mirror is reflective for the secondary radiation and is transmissive for the primary radiation. The term 'reflective' particularly refers to a reflectivity of at least 80% or 90% or 95% or 98%. The term 'transmissive' may refer to a transmittance of at least 80% or 90% or 95% or 98%. The respective numerical values may refer to an overall photometric power of the primary radiation and the secondary radiation, respectively, incident on the Bragg mirror.
According to at least one embodiment, the Bragg mirror comprises reflector layers of at least three different materials. The different materials have different refractive indices. This means that the Bragg mirror comprises a
plurality of reflector layers of a first material and a plurality of reflector layers of a second material and also a plurality of reflector layers of a third material. As an option, there could be reflector layers of a fourth material and maybe of a fifth material and so on. Preferably, there are at most eight or six or four different materials for the reflector layers.
According to at least one embodiment, the Bragg mirror comprises at least two different kinds of layer pairs. Each kind of layer pair is made up of reflective layers of two different materials. This means, for example, that a first kind of layer pairs comprises at least some of the reflector layers of the first material and at least some of the
reflector layers of the second material, a second kind of layer pairs may comprise at least some of the reflector layers of the second material or of the fourth material and at least some of the reflector layers of the third material.
According to at least one embodiment, the different kinds of layer pairs have different Brewster angles for p-polarized radiation, in particular for p-polarized secondary radiation. The primary radiation impinges on the Bragg mirror in either s or p polarization, some combination, or random
polarization .
In at least one embodiment, the optoelectronic semiconductor light source comprises a semiconductor chip configured to emit primary radiation, a Bragg mirror, and a luminescence conversion element configured to convert at least part of the primary radiation into secondary radiation having a longer wavelength. The Bragg mirror is arranged between the
semiconductor chip and the luminescence conversion element and is reflective for the secondary radiation and
transmissive for the primary radiation. The Bragg mirror comprises reflector layers of at least three different materials with different refractive indices, so that at least two different kinds of layer pairs are formed, each kind of layer pairs being made up of reflective layers of two
different materials. The different kinds of layer pairs have different Brewster angles for p-polarized radiation.
As an intrinsic property, each kind of layer pair of two specific materials as used in a Bragg mirror has a specific Brewster angle. At the Brewster angle, the reflectivity of the respective kind of layer pairs is significantly reduced and may be virtually zero for p polarized light. This means that at the Brewster angle a comparably large portion of the secondary radiation may leak through the Bragg mirror.
With the Bragg mirror described herein, by having different kinds of layer pairs with different Brewster angles, this leakage of secondary radiation can be reduced or even
eliminated. Hence, an overall efficiency of the
optoelectronic semiconductor light source can be increased.
According to at least one embodiment, the Brewster angles of the different kinds of layer pairs differ by at least 0.5° or by at least 1° or by at least 1.5° or by at least 2°.
Preferably, said difference is at least 2.5°. If there are more than two different kinds of layer pairs, this can be true pairwise.
According to at least one embodiment, at the Brewster angle of one of the different kinds of layer pairs at least one other kind of layer pairs or all other kinds of layers pairs together has/have a reflectivity for the secondary radiation of at least 20% or of at least 40% or of at least 60% or of at least 80%, in particular for p-polarized radiation. Thus, leakage of the secondary radiation at the Brewster angle can be significantly reduced or suppressed.
According to at least one embodiment, at an angle of
incidence of 0°, a reflectivity of the Bragg mirror is at most 2% in the wavelength range of the primary radiation. The term 'wavelength range of the primary radiation' refers in particular to that spectral range in which an intensity of the primary radiation is at least 5% or at least 2% of a peak intensity of the primary radiation.
According to at least one embodiment, at an angle of
incidence of 0°, a reflectivity or an average reflectivity of the Bragg mirror in the wavelength range of the secondary radiation is at least 80% or at least 90% or at least 95% or at least 98%. The term 'wavelength range of the secondary radiation' refers in particular to that spectral range in which an intensity of the secondary radiation is at least 10% or at least 5% of a peak intensity of the secondary
radiation .
According to at least one embodiment, the Bragg mirror is configured for high transmission of the primary radiation for angles of incidence of up to at least 30° or of up to at least 40° or of up to at least 50° or of up to at least 60°. In particular in the respective angular range, the
transmittance of the Bragg mirror for the primary radiation is at all angles at least 90% or at least 95% or at least 98%. Hence, even primary radiation impinging on the Bragg mirror at relatively large angles can reach the luminescence conversion element. However, the blueshift of the primary wavelength passband of the Bragg mirror will generally limit the angle of the incoming primary radiation. In many applications, such as laser activated remote phosphor (LARP) sources, where the primary radiation may have a restricted angle, this is desireable as such a mirror will reflect primary wavelength light which is scattered within the converter, back into the converter, reducing loss of backscattered primary light.
According to at least one embodiment, the Bragg mirror is configured for high reflectivity of the secondary radiation for angles of incidence of up to at least 65°. In particular in the respective angular range, the reflectivity of the Bragg mirror for the secondary radiation is at all angles at least 80% or at least 90% or at least 95%. Hence, even secondary radiation impinging on the Bragg mirror at
relatively large angles can be reflected into the desired direction with a high efficiency.
According to at least one embodiment, the Bragg mirror comprises exactly two different kinds of layer pairs. In this case, the Bragg mirror preferably comprises exactly three different materials for the reflective layers. With this configuration, while enabling cost-efficient manufacturing, a relatively high efficiency can be ensured.
According to at least one embodiment, the Bragg mirror comprises exactly three different kinds of layer pairs. In particular, in this case the Bragg mirror comprises exactly four different materials for the reflective layers. With this configuration, a very high efficiency can be ensured while manufacturing costs are still comparably moderate. According to at least one embodiment, the Bragg mirror comprises at least 3 or at least 4 or at least 5 layer pairs inclusive. This can be true for one or for some or for all kinds of layer pairs. As an alternative or in addition, the number of layer pairs per kind of layer pairs is at most 40 or at most 30 or at most 20. Preferably, the number of layer pairs per kind of layer pairs is between 4 and 18 inclusive. This configuration enables cost-efficient manufacturing.
However, greater numbers of pairs will improve overall reflectivity of secondary light. This can also improve reflectivity of high angle primary light within the converter in the case of LARP configurations.
According to at least one embodiment, the secondary radiation has a spectral width of at least 60 nm or of at least 80 nm or of at least 100 nm. As an alternative or in addition, the spectral width is at most 150 nm or at most 120 nm or at most 100 nm. Thus, the secondary radiation can be broadband radiation .
According to at least one embodiment, the primary radiation has a spectral width of at most 40 nm or of at most 30 nm or of at most 15 nm or of at most 5 nm. As an alternative or in addition, said spectral width is at least 1 nm or at least 5 nm. Thus, the primary radiation can be narrowband
radiation .
The term 'spectral width' may refer to a full width at half maximum, FWHM for short. Or it may also refer to a standard deviation in the case of Gaussian-like-shaped spectra. According to at least one embodiment, within one or some or each specific kind(s) of layer pairs, thicknesses of the reflective layers of at least one of the materials vary by at least 10% or by at least 20% or by at least 30% of a maximum thickness of the respective reflective layers within said kind of layer pairs. A variation of 20%, for example, means that there is at least one reflective layer with a thickness of at most 80% of the respective maximum thickness. This means that the thicknesses of the reflective layers vary significantly. This variation applies preferably to all kinds of reflective layers. By having significantly varying
thicknesses, a high reflectivity over a large angular range can be achieved.
According to at least one embodiment, the reflective layers have constant thicknesses in each case. Thus, there are no or no significant thickness variations concerning the reflective layers. The reflective layer can be of planar fashion, but curved reflective layers are possible in principle, too. The thickness is measured in a direction perpendicular to a main face of the respective reflective layer.
According to at least one embodiment, the different kinds of layer pairs are arranged block by block. Thus, the different kinds of layer pairs are not intermixed with each other. It is possible that the blocks directly follow one another.
Otherwise, between the blocks there could be at least one intermediate layer, in particular at most one intermediate layer .
According to at least one embodiment, at least 90% of the reflective layers have a thickness of at least 0.20 L/n or at least 0.22 L/n or at least 0.24 L/n. As an alternative or in addition, at least 90% of the reflective layers have a thickness of at most 0.49 L/n or of at most 0.45 L/n or of at most 0.41 L/n. Here, n is the refractive index, in particular at 300 K, and L is the wavelength of maximum intensity for the resepective radiation to be considered, that is, the wavelength of maximum intensity for the primary radiation to be transmitted and the wavelength of maximum intensity for the secondary radiation to be reflected; otherwise, L could be a fix wavelength like 500 nm.
According to at least one embodiment, the thickness of at least 10% or of at least 20% or of at least 40% or of at least 50% or of at least 70% of the reflective layers is at least 0.28 L/n .
The thicknesses mentioned in the previous two paragraphs can be true for all of the reflective layers or only for some kinds of reflective layers, that is for example only for the reflective layers of the first and of the second material, or only for the reflective layers of some of the blocks of layer pairs .
According to at least one embodiment, the optoelectronic semiconductor light source comprises a transmissive carrier. The Bragg mirror is mounted onto the carrier. For example, the carrier is of sapphire or of a glass.
According to at least one embodiment, the at least one semiconductor chip is a laser diode chip. Thus, the primary radiation is coherent radiation.
According to at least one embodiment, the carrier is located between the semiconductor chip and the Bragg mirror. Hence, the primary radiation runs through the carrier prior to reaching the Bragg mirror.
According to at least one embodiment, the primary radiation travels through a gas or through an evacuated area prior to reaching the carrier and/or the Bragg mirror. This means that a light-exit surface of the semiconductor chip then does not touch the carrier and/or the Bragg mirror. It is possible that an optical element is arranged between the semiconductor chip on the one hand and the carrier and/or the Bragg mirror on the other hand. By means of such an optical element, the primary radiation can be focused onto the luminescence conversion element.
According to at least one embodiment, a light-exit surface of the luminescence conversion element is small. For example, the size of the light-exit surface is at most 1 mm^ or
0.1 mm^ or o.02 mm^ . Thus, a point-like light source with a high luminous density can be achieved. Preferably, the light- exit surface is the only surface from which the secondary radiation, and as an option the primary radiation, is emitted from the luminescence conversion element, the carrier and the Bragg mirror.
According to at least one embodiment, the optoelectronic semiconductor light source further comprises an adhesive. For example, the adhesive comprises or consists of a polymer like a silicone and/or of a glass like a so-called low-temperature glass with a softening temperature of at most 350 °C. In the case of a polymer, in particular a silicone, the adhesive may be filled with a filler like glass particles or metal oxide particles to adjust the refractive index, a coefficient of thermal expansion and/or a thermal conductivity. By means of the adhesive, the semiconductor chip can be attached to the Bragg mirror, or the Bragg mirror can be attached to the carrier, or the luminescence conversion element can be attached to the carrier and/or the Bragg mirror. It is possible that the light source comprises more than one adhesive. In particular, the adhesive is an optical adhesive, that is, the primary radiation and/or the secondary radiation has/have to pass the at least one adhesive prior to leaving the light source. For example, the primary radiation runs through the adhesive prior to reaching the Bragg mirror.
According to at least one embodiment, the at least one semiconductor chip is a light-emitting diode chip. Thus, the primary radiation is incoherent radiation.
According to at least one embodiment, the adhesive has a low refractive index, in particular of at most 1.41 or of at most 1.45 or of at most 1.48 or of at most 1.55. This can be true at a wavelength of 500 nm and at a temperature of 300 K. As an alternative, the adhesive has a high refractive index of at least 1.65 or of at least 1.8.
The above-mentioned refractive indices may refer to a
wavelength of 500 nm and to a temperature of 300 K.
According to at least one embodiment, the adhesive is thin. Hence, a thickness of the adhesive is preferably at least 0.2 pm or at least 0.5 pm. As an alternative or in addition, the thickness of the adhesive is at most 2 pm or at most 4 pm or at most 10 pm. In another embodiment, the Bragg mirror can be directly deposited on to the semiconductor light source or luminescent conversion element via a number of methods known in the art, including physical vapor deposition, chemical vapor
deposition, e-beam evaporation, sputtering, atomic layer deposition, some combination of these methods, or other thin film deposition techniques.
According to at least one embodiment, the Bragg mirror forms a cage all around the luminescence conversion element except for the light-exit side of the luminescence conversion element. In particular, the luminescence conversion element is of prismatic shape and the Bragg mirror covers five of six sides of said cuboid.
According to at least one embodiment, the luminescence conversion element is a ceramic body, in particular a ceramic platelet. Thus, the luminescence conversion element can be highly thermally conductive. The luminescence conversion element can be of plane-parallel shape. Seen in top view onto the light-exit side, the luminescence conversion element may be rectangular or hexagonal or circular.
According to at least one embodiment, the secondary radiation is green light and/or yellow light and/or orange light and/or red light. As an alternative or in addition, the primary radiation is blue light and/or cyan-colored light and/or near-ultraviolet radiation. Near-ultraviolet radiation particularly refers to peak wavelengths of at least 340 nm and of at most 405 nm. When combining blue primary radiation and green/yellow/orange secondary radiation, white light may be emitted by the light source. According to at least one embodiment, the reflector layers are of metal oxides or semiconductor oxides. Binary as well as ternary or quaternary oxides can be used. For example, the materials of the reflector layers are selected from the following group: SiOg, TagOg, MgFg, ITO, ZnO, CaFg, BaFg,
AI2O3, TiOg, ZrOg, Y2O3, HfOg, IngOg, NbgOg.
Moreover, a Bragg mirror for an optoelectronic semiconductor light source is provided. Preferably, the Bragg mirror is configured like the Bragg mirror of the optoelectronic semiconductor light source as explained in conjunction with the exemplary embodiments described above. Thus, features for the Bragg mirror are also disclosed for the optoelectronic semiconductor light source and vice versa.
In at least one embodiment, the Bragg mirror comprises a plurality of reflector layers of at least three different materials with different refractive indices, and
at least two different kinds of layer pairs, each kind of layer pairs being made up of reflective layers of two
different materials. The Bragg mirror is reflective for at least one of green, yellow, orange and red light and is transmissive for at least one of blue light, cyan-colored light and near-ultraviolet radiation. The different kinds of layer pairs have different Brewster angles for p-polarized radiation .
The Bragg mirror and the optoelectronic semiconductor light source described herein are used, for example, in head lamps for vehicles like cars, in spot lights, in stage lighting, or in medical applications like endoscopes or curing substances. Further, applications in the field of spectroscopy are also possible . An optoelectronic semiconductor light source and a Bragg mirror described herein are explained in greater detail below by means of exemplary embodiments with reference to the drawings. Elements which are the same in the individual figures are indicated with the same reference numerals. The relationships between the elements are not shown to scale, however, but rather individual elements may be shown
exaggeratedly large to assist understanding.
In the figures:
Figures 1, 3 and 5 show schematic sectional representations of exemplary embodiments of an optoelectronic semiconductor light source described herein,
Figure 2 shows a schematic sectional representation of an exemplary embodiment of a Bragg mirror for optoelectronic semiconductor light sources described herein,
Figure 4 shows a schematic perspective representation of an exemplary embodiment of an optoelectronic semiconductor light source described herein,
Figures 6 and 7 show schematic tabular representations of exemplary embodiments of Bragg mirrors for optoelectronic semiconductor light sources described herein,
Figure 8 shows a representation of reflectivity of p- polarized radiation for a two material Bragg mirror with the corresponding Brewster angle region, used in a configuration such as in Figure 1,
Figure 9 shows a representation of a reflectivity of an
exemplary embodiment of a Bragg mirror for optoelectronic semiconductor light sources described herein, and
Figure 10 shows a representation of a reflectivity of a two material Bragg mirror for comparison to the
embodiments .
Many solid-state lighting (SSL) applications require high luminance and high luminous flux. Applications include projection, automotive lighting, stage lighting, medical and other areas. Often, these applications require luminance that exceeds the capabilities of LEDs. The LARP (Laser Activated Remote Phosphor) approach can generate much higher luminance than LEDs, and can do so at high power levels. Because of the low etendue of a LARP source, such light sources can couple greater power or luminous flux into these etendue-limited applications .
One such transmissive LARP system 1 is shown in the exemplary embodiment of Figure 1. Here a focused pump beam of primary radiation P, preferably generated by one or more
semiconductor chips 2 which are realized as blue laser diodes, for example, is incident on a luminescence conversion element 3, which is bonded to a transparent substrate 6 by means of an adhesive 7. Usually, the carrier 6 is of a material of high thermal conductivity, for example of sapphire . The small luminescent region pumped by the laser radiation P from the semiconductor chip 2 emits secondary radiation S in both forward and backward (towards the pump) directions.
However, only the light in the forward direction is collected by the projection system optics 8. Note that while the configuration in Figure 1 is primarily for laser excitation, also focused light from an LED could be used, albeit with greater etendue of the pump light P or possibly greater losses from LED light collection losses.
As shown in Figure 1, a dichroic Bragg mirror 4 is used to redirect the backwards emitted luminescence into the desired forward direction. Without such a dichroic Bragg mirror 4, around half of the luminescence of the secondary radiation S would go back towards the semiconductor chip 2, resulting in low overall conversion efficiency. It is also advantageous to avoid having secondary radiation S or even scattered pump light P in the carrier 6. Otherwise, the light P, S will spread laterally beyond the desired small area luminescent region, thus increasing etendue. This will degrade the desired high luminance emission. The luminescent region of the light source 1 is limited to a light-exit side 30 of the luminescence conversion element 3.
The light generated within the luminescence conversion element 3 should also escape the total internal reflection (TIR) condition at the emitting surface 30 because the converter material usually has a relatively high refractive index compared to the output medium which is usually air.
This extraction problem is usually mitigated by introducing optimized volume and/or surface scattering to couple the TIR modes into the extractable output modes. The dichroic Bragg mirror 4 is in fact part of the light extraction solution. However, these TIR effects at surfaces and additional scattering needed for light extraction create relatively strong cavity effects within the luminescence conversion element 3, which enhance any small amount of blue or converted light transmission through the dichroic Bragg mirror 4. Equivalently, the dichroic Bragg mirror 4 "sees" multiple ray bounces from the light within the luminescence conversion element 3, amplifying the loss effects which occur from the non-ideal reflecting characteristics of a real dichroic .
Therefore, high overall conversion efficiency or efficacy in the LARP system 1 shown in Figure 1 requires a dichroic Bragg mirror 4 with very high reflectivity over the desired
wavelength range and over all angles of incidence within the luminescence conversion element 3. At the same time, the dichroic Bragg mirror 4 should also transmit the partially collimated shorter wavelength pump light P, to maximize coupling of pump light P into the luminescence conversion element 3.
In Figure 2, the Bragg mirror 4 is illustrated in more detail. The Bragg mirror 4 comprises first reflector layers 41 of a first material, second reflector layers 42 of a second material, third reflector layers 43 of a third
material and fourth reflector layers 44 of a fourth material. The first an second layers 41, 42 are grouped to layer pairs 51 of a first kind, the third an fourth layers 43, 44 are grouped to layer pairs 52 of a second kind.
All the first layer pairs 51 are arranged in a first block 91, and the second layer pairs 52 are arranged in a second block 92. The blocks 91, 92 are arranged directly on top of one another. All layers 41, 42, 43, 44 are of constant thickness. The thickness of the layers 41, 42, 43, 44 is around or slightly above l/4 wherein l is in particular a peak wavelength of the secondary radiation S.
As an option, the Bragg mirror 4 can comprise a bottom layer 45 and/or a cap layer 46. The layers 45, 46 can be of the same or of different materials as/than the layers 41, 42, 43, 44. For example, the layers 45, 46 can serve as protective layers or as coupling layers. Unlike shown in Figure 2, there could also be an intermediate layer between the blocks 91,
92.
Thus, in one embodiment, multiple pairs of one set of Bragg materials are followed by multiple pairs onf a second set of Bragg materials. In another embodiment, the different pairs of materials are interleaved. It is also possible that different layer pairs could be alternated next to each other.
Other configurations of the light source 1 can also make use of dichroic coatings 4 with very high reflectivity over a wide angular range. One such example is shown in Figure 3, where the luminescence conversion element 3 is used with an LED chip 2 for either white light (partial transmission of the short wavelength LED light through the luminescence conversion element 3) or full conversion, where the LED pump light P is fully absorbed by the luminescence conversion element 3. Here the dichroic Bragg mirror 4 functions to enhance the back-reflection of the longer wavelength
converted light S towards the forward emitting direction. The Bragg mirror 4 also decouples the backward directed converted light from the LED 2, making the efficacy of the device 1 less sensitive to the LED chip 2 structure.
The Bragg mirror 4 can be applied directly to a ceramic platelet that constitutes the luminescence conversion element 3. The adhesive 7, for example a thin layer of a silicone glue, is located between a radiation main side 20 of the semiconductor chip 2 and the Bragg mirror 4.
A related application is shown in Figure 4. In this example, the luminescence conversion element 3 may be a high thermal conductivity material such as a ceramic YAG:Ce which fully absorbs the pump light P from the bonded LED chips 2 and emits longer wavelength light through only one emission surface 30. The luminescence conversion element 3 is a cuboid, for example.
The LED chips 2 can be located on more than one side surface, other than shown in Figure 4. For example, a plurality of LED chips 2 are located on two opposing side surfaces and/or on a back surface and/or on top and bottom surfaces. The light- exit side 30 may be one of the smallest side surfaces of the luminescence conversion element 3. All sides of the
luminescence conversion element 3 except for the light-exit side 30 are coated with the Bragg mirror 4. It is possible that the respective surfaces are covered with the LED chips 2 by at least 50% or 70%.
According to Figure 5, the luminescence conversion element 3 becomes narrower in the direction away from the semiconductor chip 2. The luminescence conversion element 3 can completely cover the semiconductor chip 2. All surfaces of the
luminescence conversion element 3 are coated with the Bragg mirror 4 except for the light-exit side 30. Such a configuration with a narrowing luminescence conversion element 3 can be used in all other exemplary embodiments, too. There can be more than one semiconductor chip 2 at the bottom side of the luminescence conversion element 3.
Such configurations as shown in Figures 4 and 5, for example, can emit light with lower etendue than that of the combined etendue of the semiconductor chips 2; equivalently, the device 1 will generate higher luminance than physically allowable from the semiconductor chips 2 with chip-level conversion (CLC) placed in a flat array where the
semiconductor chips do not optically couple together. As with the LARP converter, high efficacy or efficiency can
particularly be obtained if the entire ceramic phosphor 3 is coated with a very high reflective material, that is the Bragg mirror 4, on all surfaces except for the desired emitting surface 30. In one case, the semiconductor chips 2 themselves can serve as reflectors, but a masked dielectric 4 will be required on all other regions of the ceramic phosphor 3 except for the emitting side.
Alternatively, the masking step can be eliminated by using a high reflective dichroic coating 4 that allows passage of the blue pump light P. This requires the blue pass region to function over a large angular range. Note that in the case of using a masking step, one could also use an enhanced metallic coating for wide angular range reflection; however, metallic coatings are always lossy and therefore would limit the efficiency of the device 1.
Therefore, a need exists in SSL for a dichroic coating 4 that allows passage of short wavelength light P and reflects longer wavelength light S with very high transmission and very high reflectivity, respectively. As the secondary light S is incoherent, it consists of equal fractions of s- and p- polarized waves. A unique feature of this coating 4 is that it ideally has omnidirectional reflection of the longer wavelength light S, while having very high transmission for the short wavelength light P over at least a limited angular range. In cases where LED pumping is used, the transmission of the short wavelength light P must also be omnidirectional. Finally, in some SSL applications, it may also be desirable to reflect both the longer wavelength converted light and the shorter wavelength pump light P with very high
omnidirectional reflectivity.
Achieving omnidirectional reflectivity especially in
configurations such as shown in Figures 1 or 3 is
particularly challenging because the refractive index of the carrier 6 in Figure 1 or of the adhesive layer 7 in Figure 3 is often not too different from the phosphor refractive index. This implies that one cannot take full advantage of TIR effects to improve high angle reflectivity of the
luminescence generated in the phosphor 3.
Furthermore, for p-polarized radiation, most multi-layer dielectric coatings display a strong Brewster angle
transmission window that cannot be easily suppressed and therefore limits the achievable omnidirectional reflectivity of the coating. Because of the cavity effects within the phosphor 3, even small losses of reflectivity will limit the maximum achievable efficacy or efficiency of these light sources. By means of the Bragg mirror 4 described herein, improvements on the omnidirectional reflectivity of the dichroic behavior in applications such as shown in Figures 1, 3, 4 and 5 are possible by using more than the typical two dielectric coating materials in special thin film dielectric designs that suppress the Brewster transmission window.
Prior to availability of the present Bragg mirror 4, the problem of designing and fabricating a short wavelength transmitting layer and a longer wavelength reflecting layer for a transmissive LARP configuration such as shown in Figure 1 was solved by using a two-material dielectric stack based on low and high refractive index materials. For example, the low index material could be SiOg and the high index material could be TagOg. Some limitations to materials often exist, especially for LARP applications, where the bonding material could be a glass which requires high-temperature bonding. The dichroic stack consists of 40-60 layers, for example, which provide a compromise between high omnidirectional
reflectivity of the converted wavelengths and avoiding too high a thermal resistance to minimize phosphor temperatures.
Adequate structures require global optimization algorithms to generate non-periodic structures with the appropriate
wavelength passband and highest possible reflectivities. As discussed, this approach unfortunately has limitations due to the Brewster transmission window. Figure 8 shows a typical simulated reflectance plot for the dichroic/glass bonding layer in the transmissive LARP configuration shown in Figure 1. In the spectral region B, the pump light P is located. Here, Kx = sin qrr where qrr is the angle of incidence on the combined adhesive layer 7 - dichroic 4 for light rays generated within the phosphor 3.
The results show how reflectivity varies with both wavelength and angle of incidence from the phosphor to the bonding - dichroic stack, for p-polarized light. The Brewster effect is quite clear in region A, showing a reflection minimum near 0% with Kx ¾ 0.6 to 0.7. The Brewster angle qBrr for the stack, as seen by the phosphor, can be determined by the equation:
Figure imgf000026_0001
Here, ng and ng are the refractive indices for the two different dielectric stack materials. The symbol npp denotes the refractive index of the phosphor 3. For example, at
550 nm with a YAG phosphor ceramic
Figure imgf000026_0002
1.84) and
dielectric coating materials of SiOg and TagC (ng = 1.48 and ng = 2.20), Kx = 0.67, in agreement with the simulated result .
Also, for the configuration in Figure 1, it can be seen that for nearly any carrier material, a TIR condition between the phosphor and carrier - dichroic interface cannot be achieved at the Brewster angle transmission window. This can be seen by noting that the transverse wave vector Kx must be
conserved through all materials, including the dielectric stack, the adhesive layer 7, the carrier 6, and the phosphor 3. Therefore, if light is incident within the phosphor 3 at the Brewster angle qBrr, then the light will be transmitted if kB x < ksup, or equivalently,
Figure imgf000026_0003
where nsup is the refractive index of the carrier. For the example considered, kB x/kg = 1.23. Therefore, for both a glass substrate
Figure imgf000026_0004
= 1.51 for borosilicate ) or a sapphire substrate
Figure imgf000026_0005
= 1.77), Brewster angle luminescence from the phosphor 3 will be transmitted into the carrier, for any two- material dichroic. For SSL sources, such as the LARP
configuration, this results in trapped light within the carrier that will spread the effective emission spot, reducing luminescence. This is highly undesirable for
applications such as LARP. At the Brewster window, light will exit the substrate and will not be converted or used.
By employing three or more materials in the dichroic 4, one can create two different dielectric stacks with different Brewster windows, that is different material layer pairs, such that k®x/kg in Equation (2) has two different non overlapping transmission windows, closing off the Brewster window. In doing so, one can improve the overall
omnidirectionally averaged reflectivity. In the case of LARP or aperture lamp configurations, this improved reflectivity is further enhanced due to cavity effects of the partially trapped luminescence, thereby significantly increasing the overall efficiency or efficacy of the SSL source.
The advantage of the Bragg mirror 4 described herein can be expressed by calculating the photon-to-photon conversion factor, comparing a conventional single Bragg stack design to a multiple material pair, Bragg stack design. This conversion factor is the merit function which is used by the algorithms which design the details of the coatings. It is a number between zero and one, which represents the fraction of input photons which are not converted to secondary light coupled out at the front surface 30. For example, a merit function (metric value) of 0.2 implies 80% of input photons are converted to output photons exiting from the target facet in Figure 1. The list below shows results from a benchmark design, with two materials, compared with a three-material design of the same total number of layers (that is, 60 layers) but designed using both pairs of materials to cover the Brewster window.
As can be seen, all characteristics are improved: the
passband (blue pump light P) transmission is slightly more, the stopband (dichroic) is slightly more, and the overall conversion efficiency is improved by about 18%. This is a very significant improvement.
Benchmark 3-material dichroic
Average Passband 1. 12% 0.56%
Average Stopband 87 , 84% 90.47%
Metric value 0.296 0.243
Thus, by employing three or more materials in the dichroic 4, one can create multiple dielectric pairs with different
Brewster angles. For example, a stack made with TagC>5
(approximate refractive index 2.165) and SiOg (approximate refractive index 1.457) will have a Brewster angle in the lower refractive index material, that is, SiOg, of 56°, regardless of the thickness of the layers. However, the formula for the Brewster angle, corresponding to no
reflectivity for p-polarized light, for any pair of materials in terms of refractive index is given by
tan 6L =— ( 3 )
p ni
where ng and ng are the refractive indices of the two
materials, and qr is the Brewster angle in the incident medium 1.
For example, in this case the Brewster angle for Bragg pairs of SiOg/TagC>5 is 56° degrees, and for MgFg/TagOg it is 57.4°. A dichroic filter constructed, for example, by only Bragg pairs of SiOg/TagC>5, regardless of the details of the design, will have a Brewster window at that angle, and p-polarized light will escape. However, a dichroic constructed with two sets of disparate materials (SiOg/TagC>5 and, for example, indium tin oxide (ITO) (refractive index 1.858) and MgFg (refractive index 1.385)), will have two separate Brewster angles: one at 56° and the one associated with ITO/MgFg at
53°. Joined together as shown in Fig. 9, one of the two sets of pairs will have non-zero reflectivity at any angle, and so will no longer lose all photons at that angle. Note that the Brewster condition occurs at an angle of incidence of about 41° for the SiOg/TagC>5 pair.
For the Bragg mirror 4 to work effectively, the two Brewster angles have to be sufficiently different so that one pair of materials provides reflectivity at the others Brewster window .
For example, in the filter design shown in Fig. 9, the dichroic is constructed of Bragg pairs of SiOg/TagOg
(Brewster angle 56°), and indium tin oxide (ITO) /MgFg
(Brewster angle 53°) . The corresponding reflectivity plots (Figure 9, four-material, and Figure 10, two-material
MgFg/TagOg ) show that bottom overall transmittance is much higher for the single set of Bragg pairs. As the Brewster window for one pair is compensated by the reflectivity of the half-dichroic stack formed by the other pair, the overall structure has a much improved overall reflectivity. In
Figures 9 and 10, the angle of incidence is for light
incident from the phosphor side, the phosphor is a garnet like YAG, for example. These dielectric layers are fabricated similarly to
conventional dichroics, via sputtering or thermal evaporation of very precise layers. A greater variety of materials is needed (at least three separate materials, in order to have two distinct Bragg stacks), but otherwise fabrication is identical to typical dichroic filters.
The further apart the intrinsic Brewster angles, the better coverage can be achieved at the Brewster window. However, for many applications, there are not that many qualified optical coating materials with good transmission, varying refractive index, and able to withstand the necessary temperatures.
Details of the layers of exemplary dichroic coatings designed with different materials to cover the Brewster window are shown in Figures 6 and 7. These particular coatings are designed to have a passband in the blue spectral range at normal incidence, and to be omnireflective at other
wavelengths than for blue, at other angles.
The components shown in the figures follow, unless indicated otherwise, preferably in the specified sequence directly or indirectly one on top of the other. Layers which are not in contact in the figures are preferably spaced apart from one another. If lines are drawn parallel to one another, the corresponding surfaces are preferably oriented parallel to one another. Likewise, unless indicated otherwise, the positions of the drawn components relative to one another are correctly reproduced in the figures.
The invention described here is not restricted by the
description on the basis of the exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which includes in particular any combination of features in the patent claims, even if this feature or this combination itself is not explicitly
specified in the patent claims or exemplary embodiments.
This patent application claims the priority of US patent application Serial No. 16/291,679 filed on March 4, 2019, the disclosure content of which is hereby incorporated by
reference.
List of Reference Signs
1 optoelectronic semiconductor light source
2 semiconductor chip
20 radiation main side
3 luminescence conversion element
30 light-exit side
4 Bragg mirror
41 reflector layer of a first material
42 reflector layer of a second material
43 reflector layer of a third material
44 reflector layer of a fourth material
45 bottom layer
46 cap layer
51 first kind of layer pair
52 second kind of layer pair
53 third kind of layer pair
6 carrier
7 adhesive
8 optical element
91 first block of layer pairs
92 second block of layer pairs
93 third block of layer pairs
A Brewster window region
B spectral region of the primary radiation
Kx sin qrr where qrr is the angle of incidence in °
L wavelength in nm
N layer number
P primary radiation
R reflectivity in %
5 secondary radiation
T geometric layer thickness in nm

Claims

Patent Claims
1. An optoelectronic semiconductor light source comprising a semiconductor chip configured to emit primary radiation, a Bragg mirror, and
a luminescence conversion element configured to convert at least part of the primary radiation into secondary radiation having a longer wavelength, wherein
the Bragg mirror is arranged between the semiconductor chip and the luminescence conversion element,
the Bragg mirror is reflective for the secondary radiation and transmissive for the primary radiation,
the Bragg mirror comprises reflector layers of at least three different materials with different refractive indices, the Bragg mirror comprises at least two different kinds of layer pairs, each kind of layer pairs being made up of reflective layers of two different materials, and
the different kinds of layer pairs having different Brewster angles for p-polarized radiation.
2. The optoelectronic semiconductor light source according to claim 1,
wherein the Brewster angles differ by at least 1°,
so that at the Brewster angle of one of the different kinds of layer pairs at least one other kind of layer pairs has a reflectivity for the secondary radiation of at least 50%.
3. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein, at an angle of incidence of 0°,
a reflectivity of the Bragg mirror is at most 2% in the wavelength range of the primary radiation, and an average reflectivity of the Bragg mirror in the wavelength range of the secondary radiation is at least 90%.
4. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the Bragg mirror is configured for high transmission of the primary radiation for angles of incidence of up to at least 40°, and
the Bragg mirror is configured for high reflectivity of the secondary radiation for angles of incidence of up to at least 65° .
5. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the Bragg mirror comprises exactly two different kinds of layer pairs and comprises exactly three different materials for the reflective layers.
6. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the Bragg mirror comprises exactly three different kinds of layer pairs and comprises exactly four different materials for the reflective layers.
7. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the Bragg mirror comprises between 3 and 30 layer pairs inclusive per kind of layer pairs,
the secondary radiation has a spectral width of at least 80 nm, and
the primary radiation has a spectral width of at most 30 nm.
8. The optoelectronic semiconductor light source according to any one of the preceding claims, wherein within each specific kind of layer pairs, thicknesses of the reflective layers of one of the materials vary by at least 20% of a maximum thickness of the respective reflective layers within said kind of layer pairs.
9. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the different kinds of layer pairs are arranged solely block by block so that the different kinds of layer pairs are not intermixed with each other and the blocks directly follow one another.
10. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein at least 90% of the reflective layers have a
thickness of between 0.22 L/n and 0.45 L/n inclusive, at a wavelength L of 500 nm and n is the refractive index of the respective layer at a temperature of 300 K, and
the thickness of at least 10% of the reflective layers is at least 0.28 L/n .
11. The optoelectronic semiconductor light source according to any one of the preceding claims,
further comprising a transmissive carrier, the Bragg mirror being mounted onto the carrier,
wherein the semiconductor chip is a laser diode chip, the carrier is located between the semiconductor chip and the Bragg mirror, and
the primary radiation travels through a gas or through an evacuated area prior to reaching the carrier, and
the primary radiation runs through the carrier prior to reaching the Bragg mirror.
12. The optoelectronic semiconductor light source according to any one of the preceding claims,
further comprising an adhesive,
wherein the semiconductor chip is a light-emitting diode chip,
wherein the Bragg mirror is attached to the semiconductor chip by means of the adhesive so that the primary radiation runs through the adhesive prior to reaching the Bragg mirror.
13. The optoelectronic semiconductor light source according to claim 12,
wherein the adhesive has a refractive index of at most 1.55, at a wavelength of 500 nm and at a temperature of 300 K, the adhesive comprises a silicone, and
a thickness of the adhesive is between 0.5 pm and 10 pm inclusive .
14. The optoelectronic semiconductor light source according to claim 12 or 13,
wherein the adhesive has a refractive index of at least 1.7, at a wavelength of 500 nm and at a temperature of 300 K, the adhesive comprises at least one of a glass and a metal oxide, and
a thickness of the adhesive is between 0.2 pm and 4 pm inclusive .
15. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the Bragg mirror forms a cage all around the
luminescence conversion element except for a light-exit side of the luminescence conversion element.
16. The optoelectronic semiconductor light source according to any one of the preceding claims, wherein the luminescence conversion element is a ceramic platelet,
the secondary radiation is green light or yellow light or orange light or red light, and
the primary radiation is blue light or cyan-colored light or near-ultraviolet radiation.
17. The optoelectronic semiconductor light source according to any one of the preceding claims,
wherein the materials of the reflector layers are selected from the following group: SiOg, TagOg, MgFg, ITO, ZnO, CaFg,
BaFg, AlgOg, TiOg, ZrOg, YgOg, HfOg, IngOg, NbgOg.
18. A Bragg mirror for an optoelectronic semiconductor light source comprising
a plurality of reflector layers of at least three different materials with different refractive indices, and
at least two different kinds of layer pairs, each kind of layer pairs being made up of reflective layers of two
different materials, wherein
the Bragg mirror is reflective for at least one of green, yellow, orange and red light and is transmissive for at least one of blue light, cyan-colored light and near-ultraviolet radiation, and
the different kinds of layer pairs have different Brewster angles for p-polarized radiation.
PCT/EP2020/055295 2019-03-04 2020-02-28 Optoelectronic semiconductor light source and bragg mirror Ceased WO2020178176A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE112020001069.4T DE112020001069B4 (en) 2019-03-04 2020-02-28 OPTOELECTRONIC SEMICONDUCTOR LIGHT SOURCE AND BRAGG MIRROR

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US16/291,679 US10808893B2 (en) 2019-03-04 2019-03-04 Optoelectronic semiconductor light source and Bragg mirror
US16/291,679 2019-03-04

Publications (1)

Publication Number Publication Date
WO2020178176A1 true WO2020178176A1 (en) 2020-09-10

Family

ID=69723950

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2020/055295 Ceased WO2020178176A1 (en) 2019-03-04 2020-02-28 Optoelectronic semiconductor light source and bragg mirror

Country Status (3)

Country Link
US (1) US10808893B2 (en)
DE (1) DE112020001069B4 (en)
WO (1) WO2020178176A1 (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11353726B2 (en) * 2020-09-22 2022-06-07 Osram Opto Semiconductors Gmbh Optoelectronic module, method for operating an optoelectronic module and head-mounted display
KR102788595B1 (en) * 2021-04-30 2025-03-31 삼성디스플레이 주식회사 Display device
DE102021112359A1 (en) * 2021-05-12 2022-11-17 OSRAM Opto Semiconductors Gesellschaft mit beschränkter Haftung OPTOELECTRONIC LIGHTING DEVICE
TWI876413B (en) * 2023-07-05 2025-03-11 安飛特股份有限公司 Electrochromic rearview mirror assembly

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010059614A1 (en) * 2008-11-19 2010-05-27 3M Innovative Properties Company Brewster angle film for light management in luminaires and other lighting systems
US20140369025A1 (en) * 2012-01-27 2014-12-18 Osram Gmbh Lighting apparatus comprising phosphor wheel
WO2017040433A1 (en) * 2015-08-28 2017-03-09 Osram Sylvania Inc. Laser-activated remote phosphor target and system

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102015119553A1 (en) 2015-11-12 2017-05-18 Osram Opto Semiconductors Gmbh Radiation-emitting semiconductor chip, optoelectronic component with a radiation-emitting semiconductor chip and method for coating a radiation-emitting semiconductor chip
WO2017214464A1 (en) 2016-06-09 2017-12-14 Osram Sylvania Inc. Target assembly with glass-bonded wavelength converter
JP7016037B2 (en) 2017-06-30 2022-02-04 パナソニックＩｐマネジメント株式会社 Light emitter and light emitting device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010059614A1 (en) * 2008-11-19 2010-05-27 3M Innovative Properties Company Brewster angle film for light management in luminaires and other lighting systems
US20140369025A1 (en) * 2012-01-27 2014-12-18 Osram Gmbh Lighting apparatus comprising phosphor wheel
WO2017040433A1 (en) * 2015-08-28 2017-03-09 Osram Sylvania Inc. Laser-activated remote phosphor target and system

Also Published As

Publication number Publication date
US20200284401A1 (en) 2020-09-10
DE112020001069B4 (en) 2022-04-14
DE112020001069T5 (en) 2021-12-09
US10808893B2 (en) 2020-10-20

Similar Documents

Publication Publication Date Title
RU2636410C2 (en) Light-emitting device
JP6104174B2 (en) Remote phosphor LED structure
US10222540B2 (en) Light emitting device
JP5257420B2 (en) Light source device
US9921353B2 (en) Light emitting device
US20200012022A1 (en) Ceramic Wavelength Converter Having a High Reflectivity Reflector
US10808893B2 (en) Optoelectronic semiconductor light source and Bragg mirror
TWI463692B (en) Light-emitting diode module
US9033530B2 (en) Phosphor device and lighting apparatus comprising the same
EP1938393A2 (en) Illumination system with optical concentrator and wavelength converting element
TWI575781B (en) Wide-band dielectric reflector for light-emitting diodes
JP2015523722A (en) Hybrid bulb using a combination of remote phosphor LED and direct emission LED
JP6169383B2 (en) Light emitting module and light source device
US10488566B2 (en) Ceramic wavelength converter having a high reflectivity reflector
US11226082B1 (en) Optoelectronic light source
US10344947B2 (en) Light emitter and light emitting device
WO2015112946A1 (en) Ceramic wavelength converter having a high reflectivity reflector
CN106922178A (en) lighting equipment
JP7357082B2 (en) Optical device and optical device manufacturing method
CN114217499A (en) Wavelength conversion device and projection system
JP2007258466A (en) Lighting device and light emitting device
US20220205612A1 (en) Phosphor element and lighting device
JP2013092796A (en) Light source device

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 20707635

Country of ref document: EP

Kind code of ref document: A1

122 Ep: pct application non-entry in european phase

Ref document number: 20707635

Country of ref document: EP

Kind code of ref document: A1