阅读说明：本技术 一种分光谱响应增强的透射式光电阴极及其制备方法 (Transmission type photoelectric cathode with enhanced spectral response and preparation method thereof ) 是由 蔡志鹏 张景文 于 2020-06-05 设计创作，主要内容包括：本发明公开了一种分光谱响应增强的透射式光电阴极及其制备方法。该透射式光电阴极沿信号光入射方向依次包括：光学选通膜、光学玻璃、光学增透膜、缓冲层、发射层和激活层；所述光学选通膜、所述光学增透膜、所述缓冲层和所述发射层分别分为若干区域,且所述光学选通膜的各区域、所述光学增透膜的各区域、所述缓冲层的各区域和所述发射层的各区域分别一一对应,各所述区域的材料、厚度和层数根据各所述区域响应的波段进行设定。本发明提供的光电阴极能够使各波段均具有较高的量子效率,能够实现宽、窄光谱并行工作,消除宽、窄光谱光电阴极之间的应用界限。(The invention discloses a transmission-type photocathode with enhanced spectral response and a preparation method thereof. The transmission-type photocathode sequentially comprises along the incident direction of signal light: the optical gating film, the optical glass, the optical antireflection film, the buffer layer, the emitting layer and the activation layer; the optical gating film, the optical antireflection film, the buffer layer and the emitting layer are respectively divided into a plurality of regions, each region of the optical gating film, each region of the optical antireflection film, each region of the buffer layer and each region of the emitting layer are respectively in one-to-one correspondence, and the material, the thickness and the number of layers of each region are set according to the wave band responded by each region. The photocathode provided by the invention can enable each waveband to have higher quantum efficiency, can realize parallel work of wide and narrow spectrums, and eliminates the application limit between wide and narrow spectrum photocathodes.)

1. A spectral response enhanced transmission-type photocathode, comprising, in order along a signal light incident direction: the optical gating film, the optical glass, the optical antireflection film, the buffer layer, the emitting layer and the activation layer; the optical gating film, the optical antireflection film, the buffer layer and the emitting layer are respectively divided into a plurality of regions, each region of the optical gating film, each region of the optical antireflection film, each region of the buffer layer and each region of the emitting layer are respectively in one-to-one correspondence, and the material, the thickness and the number of layers of each region are set according to the wave band responded by each region.

2. The transmissive photocathode of claim 1, wherein each layer of the optical gating film is formed of MgF₂、TiO₂、SiO₂、CaF₂、Si₃N₄、Al₂O₃、MgO、HfO₂、ZrO₂、La₂O₅、BaF₂And LaF₃One single material or a composite material composed of two or more materials; the number of layers of the optical gating film is 10-300; the thickness of the optically-gated film is on the order of hundreds of nanometers to tens of micrometers.

3. The transmissive photocathode of claim 1, wherein the emissive layer is a GaAs emissive layer or an InGaAs emissive layer, and wherein the In component has a value In the range of 0-0.2.

4. The transmissive photocathode of claim 1, wherein the emission layer is comprised of alternating layers of GaAs and GaAlAs or of InGaAlAs and InGaAs.

5. The transmissive photocathode of any one of claims 1-4, wherein the thickness of each region of the emissive layer ranges from 0.05 microns to 2.5 microns; the emitting layer is p-type heavily doped and has a doping concentration of 10¹⁸～10¹⁹cm^-3In magnitude, the 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 emitting layer to the surface gradient of the emitting layer.

6. The transmission-type photocathode according to claim 1, wherein the emission layer is composed of GaAs layers and GaAlAs layers alternately grown or InGaAlAs layers alternately grown, each of the GaAlAs layers or the InGaAlAs layers has a thickness of 0 to 5 nm, an Al component having a value In a range of 0.1 to 0.6 and an In component having a value In a range of 0 to 0.2, and the In component is constant or has a gradient decreasing from an interface between the emission layer and the buffer layer to a surface of the emission layer.

7. The transmission-type photocathode of claim 1, wherein the buffer layer is an AlAs buffer layer, a GaAlAs buffer layer, or an InGaAlAs buffer layer, the buffer layer has a thickness of 50-1000 nm, Al ranges from 0.5 to 1, In ranges from 0 to 0.2, and p-type dopant concentration of 10¹⁸～10¹⁹cm^-3Of the order of magnitude, the p-type doping material being Zn orBe。

8. The transmissive photocathode of claim 7, wherein when the GaAlAs or InGaAlAs buffer layer is used as the emissive layer in a region, the buffer layer and the emissive layer in the region are the same layer, and the thickness of the buffer layer or the emissive layer in the region is 50-500 nm.

9. The enhanced spectroscopic response transmissive photocathode of claim 1, wherein each of the layers of optical antireflective film is selected from the group consisting of MgF₂、TiO₂、SiO₂、CaF₂、Si₃N₄、Al₂O₃、MgO、BaF₂、ZrO₂、La₂O₅、LaF₃And HfO₂The number of layers of the optical antireflection film is more than or equal to 1; the total thickness of the optical antireflection film is about 30 nanometers to several micrometers.

10. A method of making a spectral response enhanced transmissive photocathode for making a spectral response enhanced transmissive photocathode according to any one of claims 1-9, the method comprising:

step (1), according to wave bands or wavelengths required to respond to different areas, corresponding optical gating films are respectively manufactured in different areas of the outer surface of the optical glass and used for gating optical signals with different wave bands or wavelengths;

step (2), growing a semiconductor epitaxial structure by using 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 barrier layer, an emitting layer, a buffer layer and a protective layer; removing the protective layer by wet etching and airing under a high-purity nitrogen atmosphere; etching the emitting layer of each region to a required thickness in sequence according to the response wave bands or wavelengths of the different regions;

step (a)3) Under the vacuum condition, uniformly depositing an optical antireflection film on the surface of the buffer layer, wherein the optical antireflection film is one to many layers of optical films for antireflection in a full waveband, or one to many layers of optical films for antireflection of discrete spectra in each region; depositing a layer of SiO which is favorable for bonding on the optical antireflection film₂A film; wherein the first layer in contact with the buffer layer in the optical antireflection film is Si₃N₄And Si in the optical antireflection film of each region₃N₄The total thickness of the layers is more than or equal to 30 nanometers;

step (4), under the vacuum condition, enabling each region of the optical antireflection film and each region of the optical gating film to correspond one to one respectively, 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, removing the substrate, the smoothing layer and the barrier layer in sequence by wet etching to expose the emitting layer; according to wave bands or wavelengths required to respond in different areas, etching the areas of the emission layer corresponding to the different areas respectively in sequence to enable the areas of the emission layer to obtain required thicknesses for responding in the different areas; chemically cleaning the surface of the emitting layer, and then drying in the air under high-purity nitrogen; when the buffer layer is used as the emitting layer of a certain region, the emitting layer of the region 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 waveband;

and (6) moving the cathode assembly into an ultrahigh vacuum activation system, and carrying out Cs: o activation;

wherein the manufacturing step (1) of the optical gating film and the manufacturing steps (2) - (4) of the optical antireflection film are not in sequence.

Technical Field

The invention relates to the field of photocathodes and preparation thereof, in particular to a transmission-type photocathode with enhanced spectral response and a preparation method thereof.

Background

Negative Electron Affinity (NEA) transmission type photocathodes represented by GaAs have the advantages of high quantum efficiency, small dark current, small average energy and emission angle distribution, and the like, and are widely applied to aspects of low-light-level image intensifiers, photomultiplier tubes, Electron sources, and the like. At present, the GaAs photoelectric cathode is mainly developed towards the aspects of wide spectrum and narrow spectrum response of high quantum efficiency, particularly the wide spectrum GaAs transmission type photoelectric cathode of the ITT company in the United states is in a leading position, and the quantum efficiency of 500 plus 800 nanometers is more than 40 percent; the development of narrow spectral response mainly aims at blue-green light underwater working wave bands, the photocathode mainly adopts GaAlAs materials with high Al components, and cutoff wavelength is improved by improving the content of the Al components in the GaAlAs, so that the aim of all-weather working is fulfilled.

However, due to the structure of the transmissive GaAs photocathode, the following are provided in order from the glass window: glass window, Si₃N₄Antireflection film, GaAlAs buffer layer, GaAs absorbing layer, and Cs: and O an active layer. Therefore, the current wide-spectrum transmission-type photocathode has the following limitations: 1. as the light absorption coefficient of the photocathode is increased along with the reduction of the wavelength, the photoelectrons generated by the absorption of the short-wave light and the long-wave light are not uniformly distributed, and the photoelectrons generated by the short-wave light are mainly distributed near the interface of GaAlAs and GaAs, so that for the same cathode, when the cathode is thicker, the short-wave photoelectrons can reach the surface of the cathode through a longer path, and have larger loss than the long-wave light; when the cathode is thin, the long-wavelength light is insufficiently absorbed, resulting in a reduction in the long-wavelength quantum efficiency. Therefore, in order to take account of the response of the whole wave band, the long wave response and the short wave response cannot simultaneously achieve the optimal quantum efficiency. 2. Using only a single Si₃N₄As an anti-reflection film, the film can only increase the transmission of a narrow band, but cannot enable the whole response band to achieve a high anti-reflection effect, so that the further improvement of the whole quantum efficiency is limited; the quantum efficiency of the narrow-spectrum transmission type GaAlAs photocathode is lower than that of a GaAs photocathode, and the higher the Al component is, the lower the quantum efficiency of the cathode is, so that the current narrow-spectrum transmission type GaAlAs photocathode only having blue-green light response has the limitations that: 1. the adoption of GaAlAs with high Al component leads to the reduction of absorption coefficient, photoelectron diffusion length and surface escape probability,thus leading to a further reduction in quantum efficiency; the low Al component causes the cut-off wavelength to extend to the long wave of the non-signal light, which is not good for all-weather work; 2. the response spectrum cut-off wavelength of the GaAlAs photocathode with high Al component is slowly reduced, and the cut-off wavelength extends to a non-signal light wave band, so that signal noise is caused, and the application of the GaAlAs photocathode in higher fields of military and the like is limited; at the same time, the high Al content causes higher material defects, and the loss of photoelectrons caused by these defects further aggravates the decrease in quantum efficiency. In a word, both wide-spectrum and narrow-spectrum photocathodes have limitations, the full-spectrum quantum efficiency of the wide-spectrum photocathode cannot reach the optimum or cannot reach the optimum configuration, while the narrow-spectrum photocathode has lower quantum efficiency and generates larger noise due to non-signal light; in addition, the application ranges of the two are less overlapped. These limit further expansion of the application of transmissive NEA photocathodes.

Disclosure of Invention

The invention aims to provide a transmission-type photocathode with enhanced sub-spectral response and a preparation method thereof, wherein the photocathode can enable each waveband to have higher quantum efficiency, can realize parallel work of wide and narrow spectrums, and eliminates the application limit between the wide and narrow spectrum photocathodes.

In order to achieve the purpose, the invention provides the following scheme:

a transmission-type photocathode with enhanced spectral response sequentially comprises, along the incident direction of signal light: the optical gating film, the optical glass, the optical antireflection film, the buffer layer, the emitting layer and the activation layer; the optical gating film, the optical antireflection film, the buffer layer and the emitting layer are respectively divided into a plurality of regions, each region of the optical gating film, each region of the optical antireflection film, each region of the buffer layer and each region of the emitting layer are respectively in one-to-one correspondence, and the material, the thickness and the number of layers of each region are set according to the wave band responded by each region. Wherein the number of regions of each layer is more than or equal to 2. Because the multilayer optical gating film can realize the transmission of a required spectrum, and the optical antireflection film can realize the higher transmittance of a discrete spectrum, the cathode can be divided into a plurality of independent response regions according to the response spectrum of the transmission-type photocathode, and each region independently responds to a certain narrow waveband or wavelength (the response spectrums of the independent regions can be selected to be overlapped or not overlapped according to actual needs); for the wave band or a part of the wave band, the optical gating film can be used for realizing the gated transmission of the wave band, meanwhile, the optical antireflection film is used for improving the transmittance of the narrow wave band, and the emitting layer can reach the optimal thickness (response to the wave band or wavelength) through design, so that the optimal quantum efficiency of each narrow wave band can be achieved, or the optimal configuration of the quantum efficiency among the narrow wave bands can be achieved.

The incident light penetrates through the optical gating film to carry out primary gating on signal light wave bands, so that most non-signal light wave bands are cut off; signal light hv of different wave bands₁、hv₂、hv₃、hv₄Sequentially transmitting only corresponding regions, and then sequentially transmitting the optical glass and the optical antireflection film, wherein non-signal light is almost totally reflected by the optical gating film of the region and cannot be transmitted; after entering the buffer layer, photoelectrons generated by absorption of short-wave non-signal light by the buffer layer cannot be transported to the emitting layer, so that secondary gating is formed, and the wave band of the short-wave non-signal light is cut off; then, for each region, after non-signal light is cut off by the optical gating film and the buffer layer, only transmitted narrow-band signal light can reach the emitting layer, the signal light is absorbed by the emitting layer to generate photoelectrons, and the photoelectrons are further 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 to 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 correspondingly gate different wave bands or wavelengths respectively, and the thickness, the number of layers and the materials of the different areas are different according to different response wave bands. The material selected for each layer of the optical gating film is MgF₂、TiO₂、SiO₂、CaF₂、Si₃N₄、Al₂O₃、MgO、HfO₂、ZrO₂、La₂O₅、BaF₂And LaF₃One single material, or a composite material composed of two or more materials, but not limited to the above materials; the number of layers of the optical gating film may be 10-300; the thickness of the optically gated film is on the order of hundreds of nanometers to tens of micrometers.

The emission layer is a spectral response emission layer, and optionally has a structure of GaAs or InGaAs (In which, the value range of In component is 0-0.2), or alternatively grown multiple layers of GaAs and GaAlAs, or alternatively grown multiple layers of InGaAlAs and InGaAs. Different regions correspond to different response wave bands or wavelengths, and the materials, thicknesses and layer numbers of the different regions are different according to the response wave bands and the actual application requirements; the thickness range of each area is selected between 0.05 and 2.5 microns; the emitting layer is p-type heavily doped and has a doping concentration of 10¹⁸～10¹⁹cm^-3The magnitude is that the 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 emitting layer to the surface of the emitting layer in a gradient way; when the emitting layer contains GaAlAs or InGaAlAs, the thickness of each layer of GaAlAs or InGaAlAs is 0-5 nm, 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 emitting layer and the buffer layer to the surface of the emitting layer. Wherein, the value of In component In InGaAlAs or InGaAs ensures that the material of the emission layer can be epitaxially grown In high-quality matching or strain matching; when the emitting 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 wave bands to which the emitting layer responds, and are not necessarily equal; in addition, GaAlAs or InGaAlAs is used as a separation layer between GaAs or InGaAs in the emission layer and does not influence the transit of electrons, and the function is to obtain better flatness of the surface of each region of the cathode so as to obtain a flat surface which is more beneficial to 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 serve as the emission layer: (1) the first layer of GaAs or InGaAs which is close to the buffer layer responds to the shortest wave band; a second layer of GaAs or InGaAs adjacent to the buffer layer and the first layer of GaAs or InGaAs jointly respond to a sub-short wave band; the third layer of GaAs or InGaAs adjacent to the buffer layer and the first and second layers of GaAs or InGaAs jointly respond to a second-time short-wave band; analogizing in turn until the response of the longest wavelength band; as above, when the buffer layer is used as an emitting layer, the buffer layer responds to the shortest wavelength band at this time; the rest of the response bands are analogized in turn.

Optionally, the buffer layer is an AlAs buffer layer, a GaAlAs buffer layer, or an InGaAlAs buffer layer, the GaAlAs or InGaAlAs buffer layer has a thickness of 50-1000 nm, an Al value range of 0.5-1, an In value range of 0-0.2, and a p-type doping concentration of 10¹⁸～10¹⁹cm^-3In magnitude, the p-type doped material is Zn or Be; in addition, the buffer layer can also be used as an emitting layer in a certain region, when the GaAlAs or InGaAlAs buffer layer is used as the emitting layer in a certain region, the buffer layer and the emitting layer in the region are the same layer, the thickness of the buffer layer is 50-500 nanometers, and the thickness of the layer can be obtained by etching or not etching the buffer layer.

Optionally, the optical antireflection film is one or more layers of optical films for antireflection in a full-wave band, or one or more layers of optical films for antireflection respectively aiming at discrete spectra in different regions. For each layer of the optical antireflection film, the selected material is MgF₂、TiO₂、SiO₂、CaF₂、Si₃N₄、Al₂O₃、MgO、BaF₂、ZrO₂、La₂O₅、LaF₃And HfO₂A single material, or a composite of two or more of them, but not limited to the above materials. In the optical antireflection film, the first layer in contact with the buffer layer is Si₃N₄And Si in the optical antireflection film₃N₄The total thickness of the film 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 entrance window for facilitating imaging, and is polished on two sides, and is generally corning 9741# purple glass or corning 7056# glass.

Optionally, the active layer is Cs: and the O active layer is formed by depositing a layer of Cs with the particle size of 0.5-1.5 nanometers on the surface of the emitting layer in an ultrahigh vacuum activation system: and the O layer enables the surface of the cathode to form a negative electron affinity state which is favorable for 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), according to wave bands or wavelengths required to respond to different areas, corresponding optical gating films are respectively manufactured in different areas of the outer surface of the optical glass and used for gating optical signals with different wave bands or wavelengths;

step (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 steps along the growth direction: the device comprises a substrate, a smooth layer, a barrier layer, an emitting layer, a buffer layer and a protective layer; removing the protective layer by wet etching and airing under a high-purity nitrogen atmosphere; etching the emitting layer of each region to a required thickness in sequence according to the response wave bands or wavelengths of the different regions;

step (3), uniformly depositing an optical antireflection film on the surface of the buffer layer under a vacuum condition, wherein the optical antireflection film is one to many layers of optical films for antireflection in a full waveband, or one to many layers of optical films for antireflection of the discrete spectrum of each region respectively; depositing a layer of SiO which is favorable for bonding on the optical antireflection film₂A film; wherein the first layer in contact with the buffer layer in the optical antireflection film is Si₃N₄And Si in the optical antireflection film of each region₃N₄The total thickness of the layers is more than or equal to 30 nanometers;

step (4), under the vacuum condition, enabling each region of the optical antireflection film and each region of the optical gating film to correspond one to one respectively, 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, removing the substrate, the smoothing layer and the barrier layer in sequence by wet etching to expose the emitting layer; according to wave bands or wavelengths required to respond in different areas, etching the areas of the emission layer corresponding to the different areas respectively in sequence to enable the areas of the emission layer to obtain required thicknesses for responding in the different areas; chemically cleaning the surface of the emitting layer, and then drying in the air under high-purity nitrogen; when the buffer layer is used as the emitting layer of a certain region, the emitting layer of the region 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 waveband;

and (6) moving the cathode assembly into an ultrahigh vacuum activation system, and carrying out Cs: and O activating.

When the working temperature in the step 1 does not damage the performances of the buffer layer and the emitting layer, the step (1) for manufacturing the optical gating film is not in sequence with the steps (2) - (4) for manufacturing the optical antireflection film.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the transmission-type photocathode 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 waveband or wavelength; aiming at each independent area, the optical gating film is added on the outer surface of the glass window, so that the area can only pass through a certain wave band or wavelength in a gating mode; and simultaneously, aiming at each independent area, the thickness of the emission layer corresponding to the area is optimally designed, so that the quantum efficiency or spectral sensitivity required by each waveband is achieved, or the quantum efficiency among each waveband is optimally configured. Thus, each region responds independently, and the response spectra of the regions can also collectively form a broad spectrum. In addition, if the subsequent image fusion technique is adopted, the image fusion of all narrow bands or some narrow bands can be freely realized. Therefore, the method of independent response areas and response enhancement can improve the response sensitivity of the cathode, eliminate wide and narrow spectral response limits, meet the multifunctional application requirements of spectral detection imaging, image monitoring, multiband 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 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 it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a schematic diagram of the operation of a transmissive photocathode with enhanced spectral response in example 1 of the present invention;

FIG. 2 is a structural diagram of the photocathode with enhanced spectral response in example 1 of the present invention after bonding;

FIG. 3 is a graph showing the simulated comparison of the absorption spectra of a four-band spectral response enhanced transmission-type photocathode and a broad-spectrum conventional cathode in example 1 of the present invention;

fig. 4 is a comparison graph of the simulation of the absorption spectra of the transmissive photocathode with enhanced three-band spectral response and the conventional cathode in example 2 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.