CN111613497B - Spectral response enhanced transmission type photocathode and preparation method thereof - Google Patents
Spectral response enhanced transmission type photocathode and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a transmission type photocathode with enhanced spectral response and a preparation method thereof. The transmission type photocathode sequentially comprises the following components along the incidence direction of signal light: the optical glass comprises an optical gating film, an optical glass, an optical antireflection film, a buffer layer, an emission layer and an activation layer; the optical gating film, the optical antireflection film, the buffer layer and the emission layer are respectively divided into a plurality of areas, the areas of the optical gating film, the areas of the optical antireflection film, the areas of the buffer layer and the areas of the emission layer are respectively in one-to-one correspondence, and the materials, the thicknesses and the layer numbers of the areas are set according to the wave bands responded by the areas. The photocathode provided by the invention can enable each wave band to have higher quantum efficiency, can realize parallel operation of wide and narrow spectrums, and eliminates the application limit between the photocathodes with wide and narrow spectrums.
Description
Technical Field
The invention relates to the field of photocathodes and preparation thereof, in particular to a transmission photocathode with enhanced spectral response and a preparation method thereof.
Background
The negative electron affinity (Negative Electron Affinity, NEA) transmission type photocathode represented by GaAs has the advantages of high quantum efficiency, small dark current, small average energy and emission angle distribution and the like, and has wide application in the aspects of low-light-level image intensifiers, photomultiplier tubes, electron sources and the like. The existing GaAs photocathode mainly develops to the aspects of wide spectrum and narrow spectrum response with high quantum efficiency, particularly, the wide spectrum GaAs transmission photocathode of the American ITT company is in the leading position, and the quantum efficiency of 500-800 nanometers is more than 40%; the development of narrow spectral response mainly aims at the blue-green light underwater working wave band, the photocathode mainly adopts GaAlAs materials with high Al components, and the cut-off wavelength is improved by improving the content of the Al components in the GaAlAs, so that the purpose requirement of all-weather working is met.
However, due to the structure of the transmissive GaAs photocathode, the following are in order from the glass window: glass window, si 3 N 4 Antireflection film, gaAlAs buffer layer, gaAs absorber layer, and Cs: and an O activation layer. The current wide spectrum transmissive photocathode therefore has the following limitations: 1. the photoelectric cathode has the advantages that the light absorption coefficient is increased along with the reduction of the wavelength, so that photoelectrons generated by short-wavelength light absorption are unevenly distributed, and photoelectrons generated by short-wavelength light are mainly distributed near the interface of GaAlAs and GaAs, so that for the same cathode, when the cathode is thicker, the short-wavelength photoelectrons can reach the surface of the cathode through a longer path, and therefore, the loss is larger than that of the long-wavelength light; and when the cathode is thin, the long-wave light absorption is insufficient, resulting in a decrease in the long-wave quantum efficiency. Therefore, in order to achieve the response of the whole wave band, the long wave and short wave responses cannot reach the optimal quantum efficiency at the same time. 2. Using only a single Si 3 N 4 As an antireflection film, the antireflection film can only improve the reflection of a narrower wave band, but can not enable the whole response wave band to achieve a high antireflection effect, thereby limiting the further improvement of the overall quantum efficiency; the quantum efficiency of the narrow spectrum transmission type GaAlAs photocathode is lower than that of the GaAs photocathode, and the higher the Al component is, the lower the quantum efficiency of the cathode is, so that the narrow spectrum transmission type GaAlAs photocathode only has the following limitations: 1. the adoption of GaAlAs with high Al component leads to the reduction of absorption coefficient, photoelectron diffusion length and surface escape probability, so that the quantum efficiency is further reduced; while the low Al component leads to the extension of the cut-off wavelength to the long wave of the non-signal light, which is unfavorable for all-weather operation; 2. the response spectrum cut-off wavelength of the high Al component GaAlAs photocathode is slowly reduced, and the cut-off wavelength is extended to a non-signal optical band, so that signal noise is caused, and the application of the high Al component GaAlAs photocathode in higher fields such as military is limited; while high Al compositions cause higher material defects, the loss of photoelectrons due to these defects will further exacerbate the reduction of quantum efficiency. In summary, both wide and narrow spectrum photocathodes have limitations, and the full spectrum quantum efficiency of the wide spectrum photocathode is not optimal or is not optimally configured, while the narrow spectrum photocathodeThe quantum efficiency is low, and noise generated by non-signal light is large; in addition, the application ranges of the two are less overlapped. These limit the further expansion of the transmissive NEA photocathode applications.
Disclosure of Invention
The invention aims to provide a transmission type photocathode with enhanced spectral response and a preparation method thereof, wherein the photocathode can enable each wave band to have higher quantum efficiency, can realize parallel operation of wide and narrow spectrums, and eliminates application limit between the photocathodes with wide and narrow spectrums.
In order to achieve the above object, the present invention provides the following solutions:
a transmissive photocathode with enhanced spectral response, comprising, in order along the direction of incidence of signal light: the optical glass comprises an optical gating film, an optical glass, an optical antireflection film, a buffer layer, an emission layer and an activation layer; the optical gating film, the optical antireflection film, the buffer layer and the emission layer are respectively divided into a plurality of areas, each area of the optical gating film, each area of the optical antireflection film, each area of the buffer layer and each area of the emission layer are respectively in one-to-one correspondence, and the materials, the thicknesses and the layer numbers of each area are set according to the wave bands responded by each area. Wherein the number of areas of each layer is more than or equal to 2. The multilayer optical gating film can realize the required spectral transmission, and the optical antireflection film can realize the higher transmission rate of the discrete spectrum, so that the cathode can be divided into a plurality of independent response areas according to the response spectrum of the transmission type photocathode, each area independently responds to a certain narrow wave band or wavelength (the response spectrum between the independent areas can be selected to be overlapped or not overlapped according to actual needs); for the wave band or a part thereof, the optical gating film can be utilized to realize the gating transmission of the wave band, and the optical antireflection film is utilized to improve the transmittance of the narrow wave band, so that the emission layer reaches the optimal thickness (response to the wave band or the wavelength) through design, and the quantum efficiency of each narrow wave band can be optimized, or the quantum efficiency among the narrow wave bands can be optimally configured.
The incident light passes through the optical gating film to perform preliminary gating of the signal light wave band, so that most of non-signal light wave bands are cut off; different wavesSignal light hv of segment 1 、hv 2 、hv 3 、hv 4 Sequentially transmitting only the corresponding region and then sequentially transmitting the optical glass and the optical antireflection film, wherein the non-signal light is almost totally reflected by the optical gating film of the region and cannot transmit; after entering the buffer layer, photoelectrons generated by the absorption of the short-wave non-signal light by the buffer layer cannot be transported to the emission layer, so that secondary gating is formed, and the short-wave non-signal light band is cut off; thirdly, for each area, after the non-signal light is cut off by the optical gating film and the buffer layer, only the transmitted narrow-band signal light can reach the emitting layer, and the signal light is absorbed by the emitting layer to generate photoelectrons which are then transported to the surface and reach the active layer on the surface of the cathode; finally, due to the presence of the activation layer, the surface is in a negative electron affinity state, so that photoelectrons reaching the surface can be emitted towards the vacuum with a certain probability.
The optical gating films are manufactured on the outer surface of the optical glass, the optical gating films in different areas respectively gate different wavebands or wavelengths, and the thickness, the layer number and the materials in different areas are different according to the different response wavebands. The material selected for each layer in the optical gating film is MgF 2 、TiO 2 、SiO 2 、CaF 2 、Si 3 N 4 、Al 2 O 3 、MgO、HfO 2 、ZrO 2 、La 2 O 5 、BaF 2 And LaF 3 A single material of the above, or a composite material composed of two or more, but is not limited to the above materials; the number of layers of the optical gating film can be 10-300; the thickness of the optical gating film is about several hundred nanometers to tens of micrometers.
The emission layer is a spectral response emission layer, and is optionally structured by GaAs or InGaAs (wherein the In component takes a value ranging from 0 to 0.2), alternately grown multi-layer GaAs and GaAlAs, or alternately grown multi-layer InGaAlAs and InGaAs. Different areas correspond to different response wave bands or wavelengths, and the materials, thicknesses and layers of the different areas are different according to different response wave bands and actual application requirements; thickness of each region is takenA value range selected between 0.05 and 2.5 microns; the emitting layer is heavily doped with p-type material and has a doping concentration of 10 18 ～10 19 cm -3 The magnitude, p-type doping material is Zn or Be, the doping concentration is uniform, or the doping concentration is reduced from the interface of the buffer layer and the emission layer to the surface of the emission layer in a gradient manner; when GaAlAs or InGaAlAs is contained In the emission layer, the thickness of each layer of GaAlAs or InGaAlAs is 0-5 nanometers, the value range of Al component is 0.1-0.6, the value range of In component is 0-0.2, and the In component is unchanged or reduced In gradient from the interface of the emission layer and the buffer layer to the surface of the emission layer. The InGaAlAs or the In component In the InGaAs has a value which ensures that the material of the emitting layer can be subjected to high-quality matching or strain matching epitaxial growth; when the emission layer is a plurality of layers of alternately grown GaAs and GaAlAs (or InGaAlAs and InGaAs), the thicknesses of the layers of GaAs or InGaAs are optimally designed according to the corresponding wave bands and are not necessarily equal; in addition, gaAlAs or InGaAlAs are used as isolation layers between GaAs or InGaAs in the emission layer and do not affect electron transit, and the effect is to obtain a surface of each region of the cathode with better flatness, so as to obtain a flat surface more favorable for imaging.
Note that when the emission layer is a multilayer of GaAs and GaAlAs (or InGaAlAs and InGaAs) alternately grown, and when the buffer layer does not function as an emission layer: (1) A first layer of GaAs or InGaAs adjacent to the buffer layer, responsive to a shortest wavelength band; a second layer of GaAs or InGaAs adjacent to the buffer layer, together with the first layer of GaAs or InGaAs, is responsive to the sub-short wavelength band; a third layer of GaAs or InGaAs adjacent to the buffer layer, together with the first and second layers of GaAs or InGaAs, collectively responding to a second short wave band; and so on, until the longest wavelength band is responded to; in the same way, when the buffer layer is used as an emission layer, the buffer layer responds to the shortest wave band at the moment; the remaining response bands are analogized in turn.
Optionally, the buffer layer is AlAs buffer layer or GaAlAs buffer layer or InGaAlAs buffer layer, wherein the thickness of the GaAlAs or InGaAlAs buffer layer is 50-1000 nm, the value range of Al is 0.5-1, the value range of in is 0-0.2, and the p-type doping concentration is 10 18 ～10 19 cm -3 In the order of magnitude of the magnitude,the p-type doping material is Zn or Be; in addition, the buffer layer can also be used as an emission layer in a certain area, and when the GaAlAs or InGaAlAs buffer layer is used as the emission layer in a certain area, the buffer layer and the emission layer in the certain area are the same layer, the thickness of the buffer layer is 50-500 nanometers, and the layer thickness can be obtained by etching or not etching the buffer layer.
Optionally, the optical antireflection film is one or more layers of optical film with full-band antireflection, or one or more layers of optical film with antireflection for different regions of discrete spectra respectively. Each layer of the optical antireflection film is made of MgF 2 、TiO 2 、SiO 2 、CaF 2 、Si 3 N 4 、Al 2 O 3 、MgO、BaF 2 、ZrO 2 、La 2 O 5 、LaF 3 And HfO 2 A single material of (a) or a composite material of two or more of them, but is not limited to the above materials. Wherein, in the optical antireflection film, the first layer contacted with the buffer layer is Si 3 N 4 And Si in the optical antireflection film 3 N 4 The total thickness of the polymer is more than or equal to 30 nanometers; the number of layers of the optical antireflection film is more than or equal to 1, and the thickness of the optical antireflection film is about 30 nanometers to several micrometers.
Optionally, the optical glass is a signal light incident window beneficial to imaging, and is polished on two sides, and is typically corning 9741# transparent purple glass or corning 7056# glass.
Optionally, the activating layer is Cs: an O activation layer is formed by depositing a layer of Cs of 0.5-1.5 nanometers on the surface of the emission layer in an ultrahigh vacuum activation system: and an O layer, which enables the surface of the cathode to form a negative electron affinity state which is beneficial to photoelectron emission.
The invention also provides a preparation method of the transmission type photocathode with enhanced spectral response, which comprises the following steps:
step (1), respectively manufacturing corresponding optical gating films in different areas on the outer surface of the optical glass according to the wave bands or the wavelengths of the responses required by the responses of the different areas, so as to gate the optical signals of the different wave bands or the wavelengths;
and (2) growing a semiconductor epitaxial structure by utilizing a Metal Organic Chemical Vapor Deposition (MOCVD) technology or a Molecular Beam Epitaxy (MBE) technology, wherein the semiconductor epitaxial structure sequentially comprises the following components in the growth direction: the device comprises a substrate, a smooth layer, a blocking layer, an emitting layer, a buffer layer and a protective layer; wet etching to remove the protective layer and airing in a high-purity nitrogen atmosphere; etching the required thickness on the emitting layer of each region according to the response wave bands or the wavelength of different regions;
uniformly depositing an optical antireflection film on the surface of the buffer layer under a vacuum condition, wherein the optical antireflection film is one or more layers of optical films with full antireflection wavebands or one or more layers of optical films with antireflection for discrete spectra of each region respectively; depositing a layer of SiO which is favorable for bonding on the optical anti-reflection film 2 A film; wherein the first layer of the optical antireflection film, which is contacted with the buffer layer, is Si 3 N 4 And Si in the optical antireflection film of each region 3 N 4 The total thickness of the layer is more than or equal to 30 nanometers;
step (4), under the vacuum condition, enabling each area of the optical antireflection film to correspond to each area of the optical gating film one by one, and thermally bonding the surface of the buffer layer and the optical glass together;
step (5), under the condition of protecting the optical gating film, sequentially removing the substrate, the smooth layer and the blocking layer by wet etching to expose the emitting layer; etching each region of the emission layer corresponding to different regions in sequence according to the wave bands or the wave lengths of the responses required by the different regions, so that each region of the emission layer obtains the required thickness for the responses of the different regions; chemically cleaning the surface of the emission layer, and airing under high-purity nitrogen; when the buffer layer is used as the emission layer of a certain area, the emission layer of the area is etched and removed to expose the buffer layer, and then the thickness of the buffer layer is processed according to the requirement of a response wave band;
step (6), moving the cathode assembly into an ultrahigh vacuum activation system, and carrying out Cs on the surface of the emission layer: o activates.
When the working temperature of the step 1 does not damage the performances of the buffer layer and the emission layer, the manufacturing step (1) of the optical gating film and the manufacturing steps (2) - (4) of the optical antireflection film are not sequential.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the transmission type photoelectric cathode with enhanced spectral response comprises an optical gating film, a glass window, an optical antireflection film, a buffer layer, an emission layer and an activation layer, wherein the cathode surface is divided into a plurality of independent response areas, and each area responds to a certain wave band or wavelength; for each independent area, an optical gating film is added on the outer surface of the glass window, so that the area only transmits a certain wave band or wavelength in a gating way; meanwhile, aiming at each independent area, the thickness of the corresponding emission layer of the area is optimally designed, so that the quantum efficiency or spectral sensitivity required by each wave band is achieved, or the quantum efficiency among the wave bands is optimally configured. In this way, each region responds independently, and the response spectra of the regions can also together form a broad spectrum. In addition, if the subsequent image fusion technology is adopted, the image fusion of all or a few of the narrow wave bands can be freely realized. Therefore, the method of independent and enhanced response of a plurality of response areas can improve the response sensitivity of the cathode, eliminate the wide and narrow spectral response limits, realize the multi-functional application requirements of spectral detection imaging, image monitoring, multi-band image fusion and the like, and greatly expand the application of the transmission type photocathode.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram showing the operation of a transmissive photocathode with spectral response enhancement in example 1 of the present invention;
FIG. 2 is a diagram showing the structure of the bonded photocathode with enhanced spectral response in example 1 of the present invention;
FIG. 3 is a graph showing the simulated comparison of absorption spectra of a transmissive photocathode with enhanced four-band split spectral response and a wide-spectrum conventional cathode according to example 1 of the present invention;
fig. 4 is a graph showing the comparison of absorption spectrum simulation of a transmissive photocathode with enhanced spectral response in three-band spectral response in example 2 of the present invention and a conventional cathode.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
The response of the transmissive photocathode provided in this embodiment is 300-910 nm spectrum, and the schematic working structure is shown in fig. 1. The transmission type photoelectric cathode structure sequentially comprises the following components along the incidence direction of optical signals: tiO (titanium dioxide) 2 /SiO 2 Optical gating film 1, optical glass 2, optical antireflection film 3, ga 0.1 Al 0.9 As buffer layer 4, gaAs emission layer 5, cs: o-activated layer 6. The GaAs emission layer 5 is divided into four areas of 0-50 nm 5-1, 400-600 nm 5-2, 1000-1200 nm 5-3 and 1600-2000 nm 5-4 according to the thickness, and the following wave bands are respectively responded correspondingly: 300-400 nm, 400-550 nm, 550-700 nm and 700-910 nm, the transmissive cathode structure provided in this embodiment is also divided into four regions from the optical gating film 1 to the buffer layer 4 according to the response band, and the four regions are in one-to-one correspondence with each other.
The TiO 2 /SiO 2 The optical gating film 1, which is used as the optical gating film in the present embodiment,the optical gating film 1 is made of TiO and is arranged on the outer surface of the optical glass 2 2 And SiO 2 Alternately grown, non-uniform thickness optical gating films with spectral gating effects on 300-910 nm. The optical gating films 1-1 to 1-4 have gating effects on the following wave bands in sequence: 300-400 nm, 400-550 nm, 550-700 nm, 700-910 nm. The TiO 2 /SiO 2 The four areas of the optical gating film 1-1 to 1-4 are respectively non-uniform thickness dielectric films obtained based on the following structural optimization:
the TiO 2 /SiO 2 Optical gating film 1-1, (0.5LH0.5L) 15 A center wavelength 464 nanometers;
the TiO 2 /SiO 2 The optical gating film 1-2 comprises the following components in sequence from the surface of the optical glass:
(0.5(0.5HL0.5H) 10 )((0.5LH0.5L) 10 )(1.25(0.5LH0.5L) 10 )(1.6(0.5LH0.5L) 10 ) The center wavelength is 630 nanometers at this time.
The TiO 2 /SiO 2 The optical gating film 1-3 sequentially comprises the following components from the surface of the optical glass: (0.3 (0.5HL0.5H) 10 )(0.40(0.5HL0.5H) 10 )(0.55(0.5HL0.5H) 10 )((0.5LH0.5L) 10 ) The center wavelength is 815 nanometers at this time.
The TiO 2 /SiO 2 The optical gating films 1-4 sequentially comprise the following components from the surface of the optical glass: (0.3 (0.5HL0.5H) 12 )(0.41(0.5HL0.5H) 12 )(0.545(0.5HL0.5H) 12 )((0.5LH0.5L) 12 )
At this time, the center wavelength is 1060 nanometers.
Wherein H represents high refractive index TiO 2 L represents SiO with low refractive index 2 And H, L each represents the thickness of the layer being 1/4 of the central wavelength of the region, and the upper right corner mark represents the number of cycles.
The GaAs emission layer 5 is divided into four areas 5-1 to 5-4, and the thickness of each area 5-1 to 5-4 is as follows: 0-50 nm, 400-600 nm, 1000-1200 nm, 1600-2000 nm, and p-type doping concentration of 10 19 cm -3 With uniform doping of a magnitude, or with a doping concentration defined by the buffer layer/the emitter layer boundaryFrom surface to surface 10 19 cm -3 To 10 18 cm -3 Gradually lowering;
the Ga 0.1 Al 0.9 The As buffer layer 4 is divided into four areas of 4-1 to 4-4, the thickness is 100-200 nanometers, the As buffer layer corresponds to 5-1 to 5-4 of the emitting layer one by one, and the p-type doping concentration is 10 18 ～10 19 cm -3 . Wherein, the 1-1 region of the buffer layer in this example is used as the emission layer;
the optical antireflection film 3 is an optical medium film with antireflection performance, and has a structure divided into four areas of 3-1 to 3-4, and corresponds to the 1-1 to 1-4 areas of the optical gating film one by one: wherein the optical anti-reflection film 3-1 region is 35 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical antireflection film 3-2 area is 55 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical anti-reflection film 3-3 region is 77.5 nanometers of Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical antireflection film 3-4 is 109.5 nm Si 3 N 4 ；
The Cs: the O-activated layer 6 is Cs with a thickness of about 1 nm deposited on the GaAs absorption-emission layer surface under ultra-high vacuum conditions: and an O-activating layer, thereby placing the cathode surface in a NEA state.
The preparation method of the photocathode provided in example 1 is as follows, see fig. 1 and fig. 2:
step (1): the optical glass 2 is divided into four areas from 2-1 to 2-4; sequentially manufacturing the optical gating films 1-1 to 1-4 in four areas of the outer surface 2-1 to 2-4 of the optical glass 2 by using a mask plate;
step (2): a GaAs smoothing layer 8, a GaAlAs barrier layer 7, a 2000 nm GaAs emission layer 5 (corresponding to FIG. 1), 100-200 nm Ga are grown on a high quality GaAs substrate 9 (see FIG. 2) in sequence by using MOCVD or MBE semiconductor epitaxial growth technique 0.1 Al 0.9 An As buffer layer 4 (corresponding to fig. 1), a GaAs protection layer 10;
step (3): removing the GaAs protective layer 10 by chemical etching and airing under high-purity nitrogen; further, under vacuum conditions, in the Ga 0.1 Al 0.9 The surfaces of four areas 4-1 to 4-4 of the As buffer layer 4 are sequentially depositedThe optical antireflection film 3 is also divided into four areas of 3-1 to 3-4, and the area of the optical antireflection film 3-1 is: 35 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical antireflection film 3-2 region: 55 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical antireflection film 3-3 region: 77.5 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical antireflection film 3-4:109.5 nm Si 3 N 4 ；
Then, a layer of SiO is deposited on the uppermost surface of the optical anti-reflection film 3 2 The film is used for eliminating the high-low non-uniformity of the four areas 3-1 to 3-4 of the optical antireflection film 3, so that the uniformity and flatness favorable for bonding and imaging are achieved on the whole surface of the optical antireflection film 3;
step (4): under the heating condition, each area of the antireflection film 3 corresponds to each area of the optical gating film 1 one by one, and the surface of the optical antireflection film 3 and the inner surface of the optical glass 2 are thermally bonded together (meanwhile, the optical gating film 1 is protected from being damaged), as shown in fig. 2;
step (5): under the condition of protecting the optical gating film 1, sequentially removing the GaAs substrate 9, the GaAs smoothing layer 8 and the GaAlAs barrier layer 7 by a chemical corrosion method to expose the GaAs emission layer 5; the emitting layer 5 is divided into four areas 5-1 to 5-4, each area corresponds to the 1-1 to 1-4 areas of the optical gating film 1 one by one, the four areas 5-1 to 5-4 of the emitting layer 5 are sequentially etched, and the thicknesses of the areas 5-1 to 5-4 are sequentially as follows: 0-50 nm 5-1, 400-600 nm 5-2, 1000-1200 nm 5-3, 1600-2000 nm 5-4; after chemically cleaning the surface of the GaAs emission layer 5, drying the GaAs emission layer under high-purity nitrogen;
step (6): transferring into an ultrahigh vacuum activation system for Cs: o activating, and depositing a layer of Cs of about 1 nanometer on the surface of the GaAs emission layer: the O-activating layer 6 is brought to a negative electron affinity state.
Referring to a comparison between the absorption spectrum of the transmissive photocathode and the absorption spectrum of the conventional transmissive photocathode provided in embodiment 1 shown in fig. 3, it can be seen that the transmissive photocathode provided in embodiment 1 achieves the purpose of spectral response by the common modulation of the multilayer optical gating film, the optical antireflection film and the GaAs emission layer, the different regions only respond to one section of spectrum, the overlapping of the regions is less, and all the wave bands form a response to the full wave band, the absorption cut-off ratio of each region reaches about 2-4 orders of magnitude, and the non-signal wave band light is well suppressed; meanwhile, the optical gating film and the optical antireflection film in each region have high antireflection effect. Compared with the traditional cathode with a wide spectrum, the cathode has higher absorptivity, particularly, the absorption rate is 10-16% higher in the 350-368 and 350-397 nanometer wave bands, the absorption rate is 10-27% higher in the 400-448 nanometer wave bands, the absorption rate is 10-13% higher in the 523-600 wave bands, and the absorption rate is 5-13% higher in the 713-882 nanometer wave bands, so that the whole transmission type photocathode is superior to the traditional transmission type photocathode, has the spectral response capacity with high signal to noise ratio and higher quantum efficiency, can be applied to detection imaging, image monitoring and multiband image fusion in various fields, and has wider application prospect.
Example 2
The transmission type photocathode assembly structure in this embodiment sequentially comprises from bottom to top: tiO (titanium dioxide) 2 /SiO 2 Multilayer optical gating film, optical glass, optical antireflection film, and In 0.15 Ga 0.25 Al 0.6 As buffer layer, in 0.15 Ga 0.85 As emission layer, cs: and an O activation layer.
The TiO 2 /SiO 2 The optical gating film is made on the outer surface of the optical glass and comprises alternately grown TiO 2 And SiO 2 Has gating function. The optical gating film is divided into three areas of 1-1 to 1-3, and has gating effect on the following wave bands in sequence: 400-5500 nm, 550-710 nm, 710-910 nm.
The p-type doping concentration of the emitting layer is 10 19 cm -3 With a uniform doping of a magnitude, or with a doping concentration from the buffer layer/emissive layer interface to the surface of 10 19 cm -3 To 10 18 cm -3 Gradually decrease In 0.15 Ga 0.25 Al 0.6 P-type doping concentration of As 10 17 -10 18 cm -3 The method comprises the steps of carrying out a first treatment on the surface of the The emission layer 5 is divided into three areas of 5-1 to 5-3, and the three areas are sequentially 5-1:400 nm of GaAs and a silicon nitride layer,5-2:400 nm GaAs/5 nm GaAlAs/800 nm GaAs,5-3:400 nm GaAs/5 nm GaAlAs/800 nm GaAs, which are in one-to-one correspondence with 1-1 to 1-3 regions of the optical gating film;
the GaAlAs buffer layer is divided into three areas of 4-1 to 4-3, and Al components of 0.8 to 0.9 are in one-to-one correspondence with the 1-1 to 1-3 areas of the optical gating film. The thickness of the three regions of the buffer layer is 100-200 micrometers, and the p-type doping concentration is 10 18 ～10 19 cm -3 Magnitude, or doping concentration, from interface of the buffer layer with the emissive layer to emissive layer surface of 10 19 cm -3 To 10 18 cm -3 Gradually lowering;
the optical antireflection film is divided into three areas of 3-1 to 3-3, and the three areas are in one-to-one correspondence with the 1-1 to 1-3 areas of the optical gating film; wherein, the area of the optical antireflection film 3-1 is as follows from the surface of the glass window: 43 nm Si 3 N 4 16 nm SiO 2 48.5 nm Si 3 N 4 73.5 nm SiO 2 60 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The optical antireflection film 3-2 area is formed by the following steps from the surface of the glass window: 90 nm Si 3 N 4 7.5 nanometer SiO 2 90 nm Si 3 N 4 109 nm SiO 2 73.5 nm Si 3 N 4 The method comprises the steps of carrying out a first treatment on the surface of the The area of the optical antireflection film 3-3 is sequentially from the surface of the glass window: 194 nm Si 3 N 4 141.5 nm SiO 2 107 nm Si 3 N 4 ；
The Cs: the O-activated layer is the same as in example 1.
The preparation method of the photocathode in example 2 is as follows:
step (1): in the same way as in the embodiment 1, the optical gating film is manufactured on the outer surface of the optical glass and is divided into three areas of 1-1 to 1-3;
step (2): the same as in the embodiment 1, wherein the emission layer is replaced by 400 nm GaAs/5 nm GaAlAs/800 nm GaAs, the buffer layer 4 is replaced by GaAlAs, and the Al composition is 0.8-0.9, and three areas of the buffer layer and the emission layer are uniformly corresponding to 1-1 to 1-3 areas of the optical gating film;
step (3): the same as in example 1, wherein the number of layers and the thickness of each layer of the optical antireflection film are different according to the response area, as described in example 2;
step (4): as in example 1;
step (5): the same as in example 1, wherein the emission layer 5 is replaced with 400 nm GaAs/5 nm GaAlAs/800 nm GaAs, and the thickness of each region from 1-1 to 1-3 is sequentially made to reach 400 nm GaAs thickness, 400 nm GaAs/5 nm GaAlAs/800 nm GaAs by etching;
step (6): as in example 1.
The transmission type photocathode provided by the embodiment, as shown in fig. 4, responds to three spectrum divisions from the 400-910 nanometer wave band range, and the non-signal light wave band is well suppressed; thin GaAlAs is adopted as an isolation layer between GaAs layers, and the emission surface is more beneficial to imaging; the quantum efficiency of the transmissive photocathode provided in this embodiment is generally higher than that of the conventional cathode, especially 400-420 nm, 421-550 nm, 551-680 nm. The absorption rate of 706-880 nanometers is higher than that of the traditional cathodes of 27-29%, 6-26%, 5-13% and 5-18% respectively, so that the photoelectric cathode provided by the invention has higher response cut-off ratio and higher quantum efficiency on the response of each spectrum, and is expected to be widely applied in the fields of wide and narrow spectral response.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (10)
1. A transmissive photocathode with enhanced spectral response, characterized by comprising, in order along the direction of incidence of signal light: the optical glass comprises an optical gating film, an optical glass, an optical antireflection film, a buffer layer, an emission layer and an activation layer; the optical gating film, the optical antireflection film, the buffer layer and the emission layer are respectively divided into a plurality of areas, the areas of the optical gating film, the areas of the optical antireflection film, the areas of the buffer layer and the areas of the emission layer are respectively in one-to-one correspondence, and the materials, the thicknesses and the layer numbers of the areas are set according to the wave bands responded by the areas;
the cathode is divided into a plurality of independent response areas, each area is independently responsive to a certain narrow wave band or wavelength, the optical gating film is used for gating and transmitting signal light of the wave band or wavelength, the signal light after being selected and transmitted reaches the optical antireflection film, the signal light reaches the buffer layer after being transmitted by the optical antireflection film, and the buffer layer is used for conducting secondary gating on optical signals of the wave band or wavelength, so that the short wave non-signal light wave band is cut off; for each area, after the non-signal light is cut off by the optical gating film and the buffer layer, only the transmitted narrow-band signal light can reach the emitting layer, and the signal light is absorbed by the emitting layer to generate photoelectrons, and the photoelectrons are transported to the surface and reach the active layer on the surface of the cathode; finally, the activation layer enables the surface to be in a negative electron affinity state, so that photoelectrons reaching the surface can be emitted to vacuum with a certain probability;
the material selected for each layer of the optical gating film is MgF 2 、TiO 2 、SiO 2 、CaF 2 、Si 3 N 4 、Al 2 O 3 、MgO、HfO 2 、ZrO 2 、La 2 O 5 、BaF 2 And LaF 3 A single material of (a) or a composite material composed of two or more materials; the material selected for each layer of the optical antireflection film is MgF 2 、TiO 2 、SiO 2 、CaF 2 、Si 3 N 4 、Al 2 O 3 、MgO、BaF 2 、ZrO 2 、La 2 O 5 、LaF 3 And HfO 2 A single material of (a) or a composite material of two or more of the above; the buffer layer is an AlAs buffer layer or a GaAlAs buffer layer or an InGaAlAs buffer layer.
2. The transmissive photocathode with enhanced spectral response according to claim 1, wherein the number of layers of the optical gating film is 10-300; the thickness of the optical gating film is several hundred nanometers to tens of micrometers.
3. The transmissive photocathode with enhanced spectral response according to claim 1, wherein the emission layer is a GaAs emission layer or an InGaAs emission layer, wherein the In component has a value ranging from 0 to 0.2.
4. The transmissive photocathode of claim 1, wherein the emission layer is composed of alternately grown GaAs layers and GaAlAs layers or is composed of alternately grown InGaAlAs layers and InGaAs layers.
5. The transmissive photocathode with enhanced spectral response according to any one of claims 1 to 4, wherein the thickness of each region of the emission layer has a value ranging from 0.05 to 2.5 μm; the emitting layer is heavily doped with p-type material and has a doping concentration of 10 18 ～10 19 cm -3 The magnitude, p-type doped material is Zn or Be; the doping concentration is uniform or the doping concentration is reduced from the interface of the buffer layer and the emission layer to the surface gradient of the emission layer.
6. The transmissive photocathode of claim 1, wherein the emission layer is composed of alternately grown GaAs layers and GaAlAs layers, or alternatively grown InGaAlAs layers and InGaAlAs layers, each GaAlAs layer or InGaAlAs layer has a thickness of 0 to 5 nm, an Al composition value ranging from 0.1 to 0.6, an In composition value ranging from 0 to 0.2, and an In composition is unchanged or reduced In gradient from the interface of the emission layer and the buffer layer to the surface of the emission layer.
7. The enhanced spectral response transmissive photocathode of claim 1 wherein the buffer layer has a thickness of 50-1000 nm, an Al value in the range of 0.5-1, an in value in the range of 0-0.2, and a p-type doping concentration of 10 18 ～10 19 cm -3 The p-type dopant is Zn or Be.
8. The transmissive photocathode of claim 7, wherein when the GaAlAs or InGaAlAs buffer layer is used as the emission layer in a certain region, the buffer layer and the emission layer in the region are the same layer, and the thickness of the buffer layer or the emission layer in the region is 50-500 nm.
9. The transmissive photocathode with enhanced spectral response according to claim 1, wherein the number of layers of the optical antireflection film is not less than 1; the total thickness of the optical antireflection film is 30 nm to several micrometers.
10. A method for preparing a transmissive photocathode with enhanced spectral response, characterized in that the method is used for preparing a transmissive photocathode with enhanced spectral response according to any one of claims 1 to 9, comprising:
step (1), respectively manufacturing corresponding optical gating films in different areas on the outer surface of the optical glass according to the wave bands or the wavelengths of the responses required by the responses of the different areas, so as to gate the optical signals of the different wave bands or the wavelengths;
step (2), growing a semiconductor epitaxial structure by utilizing a metal organic chemical vapor deposition technology or a molecular beam epitaxy technology, wherein the semiconductor epitaxial structure sequentially comprises the following steps along the growth direction: the device comprises a substrate, a smooth layer, a blocking layer, an emitting layer, a buffer layer and a protective layer; wet etching to remove the protective layer and airing in a high-purity nitrogen atmosphere; etching the required thickness on the emitting layer of each region according to the response wave bands or the wavelength of different regions;
uniformly depositing an optical antireflection film on the surface of the buffer layer under a vacuum condition, wherein the optical antireflection film is one or more layers of optical films with full antireflection wavebands or one or more layers of optical films with antireflection for discrete spectra of each region respectively; depositing a layer of SiO which is favorable for bonding on the optical anti-reflection film 2 A film; wherein the first layer of the optical antireflection film, which is contacted with the buffer layer, is Si 3 N 4 And Si in the optical antireflection film of each region 3 N 4 The total thickness of the layer is more than or equal to 30 nanometers;
step (4), under the vacuum condition, enabling each area of the optical antireflection film to correspond to each area of the optical gating film one by one, and thermally bonding the surface of the buffer layer and the optical glass together;
step (5), under the condition of protecting the optical gating film, sequentially removing the substrate, the smooth layer and the blocking layer by wet etching to expose the emitting layer; etching each region of the emission layer corresponding to different regions in sequence according to the wave bands or the wave lengths of the responses required by the different regions, so that each region of the emission layer obtains the required thickness for the responses of the different regions; chemically cleaning the surface of the emission layer, and airing under high-purity nitrogen; when the buffer layer is used as the emission layer of a certain area, the emission layer of the area is etched and removed to expose the buffer layer, and then the thickness of the buffer layer is processed according to the requirement of a response wave band;
step (6), moving the cathode assembly into an ultrahigh vacuum activation system, and carrying out Cs on the surface of the emission layer: o activation;
wherein, the manufacturing steps (1) and (2) - (4) of the optical gating film are not in sequence.
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