Transmission-type GaAs-based photoelectric cathode and application thereof

Abstract

The invention relates to the technical field of photoelectric cathodes, in particular to a transmission-type GaAs-based photoelectric cathode. The transmission-type GaAs-based photoelectric cathode provided by the invention comprises a SiO2 layer, a grating layer, a buffer layer, an emission layer and an activation layer which are sequentially laminated along a light incidence direction, the grating layer comprises a Si3N4 optical thin film and a dielectric grating structure of a non-axisymmetric periodic unit; the dielectric grating structure is an incident grating interface and / or an emergent grating interface. According to the transmission-type GaAs-based photoelectric cathode, under the condition that the thickness of the cathode is not increased, the overall response performance of the cathode is greatly improved, and especially the long-wave threshold wave band which is not fully absorbed is absorbed; meanwhile, long-wave and short-wave responses can be considered; and polarization response of a certain wavelength of a long-wave threshold can be realized based on application.

Description

Technical Field

[0001] The present invention relates to the technical field of photocathode, and in particular to a transmission-type GaAs-based photocathode and application thereof. Background Art

[0002] The conventional structure of a transmissive GaAs-based photocathode is glass window / Si3N4 anti-reflection film / buffer layer / emitter layer / Cs:O activation layer. The signal light is incident from one side of the glass window, passes through the anti-reflection film and buffer layer in sequence, and is absorbed when it reaches the emission layer, and excites photoelectrons. The photoelectrons travel to the thin Cs:O activation layer and are emitted into the vacuum, forming a vacuum photocurrent. GaAs-based photocathode materials refer to high-quality semiconductor heterojunction epitaxial materials grown on high-quality GaAs semiconductors as substrates, where the emission layer materials are GaAs, InGaAs (In component ≤ 0.2), GaAsP (P component ≤ 0.5), AlGaAs (Al component ≤ 0.7), etc. Transmissive GaAs-based photocathodes are represented by GaAs photocathodes, which are the core photoelectric conversion components of vacuum detection and imaging devices such as low-light image intensifiers and photomultiplier tubes, and have the advantages of high quantum efficiency and low dark current. Among them, quantum efficiency is one of the most important technical indicators of the photocathode. At present, the highest quantum efficiency of GaAs-based photocathodes such as transmissive GaAs, AlGaAs, InGaAs, and GaAsP has reached 40-50%.

[0003] However, for the traditional structure of the photocathode, as the wavelength of light increases, the absorption coefficient of the photocathode emission layer gradually decreases. Therefore, for the traditional structure of the transmission-type GaAs-based photocathode, the light absorption coefficient near the long-wave threshold is small, resulting in insufficient light absorption near this band. Although the light absorption rate can be improved by increasing the thickness of the emission layer, for the transmission-type photocathode, photoelectrons transit from the cathode body to the surface. When the cathode emission layer is too thick, the short-wave response is reduced; and when the emission layer is too thin, the long-wave light absorption is insufficient and the long-wave response is reduced. Therefore, if the emission layer is too thick or too thin, the light response will be reduced. Therefore, how to improve the light absorption in the long-wave threshold band without reducing the short-wave response and achieve both short-wave and long-wave responses is an important direction for the future development of transmission-type photocathodes. Summary of the invention

[0004] The purpose of the present invention is to provide a transmission-type GaAs-based photocathode and its application. The transmission-type GaAs-based photocathode greatly improves the overall response performance of the cathode without increasing the thickness of the cathode, especially the long-wave threshold band with insufficient absorption, while being able to take into account both long-wave and short-wave responses, and can realize a polarization response of a certain wavelength in the long-wave threshold band according to actual applications.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a transmissive GaAs-based photocathode, which comprises a SiO2 layer, a grating layer, a buffer layer, an emission layer and an activation layer stacked in sequence along the light incident direction;

[0007] The grating layer comprises a Si3N4 optical film and a dielectric grating structure of a non-axisymmetric periodic unit; the dielectric grating structure is an incident grating interface and / or an exit grating interface.

[0008] Preferably, the incident grating interface is a SiO2 / Si3N4 grating interface, and the exit grating interface is a Si3N4 / buffer layer grating structure.

[0009] Preferably, the dielectric grating structure is a one-dimensional grating structure or a two-dimensional grating structure.

[0010] Preferably, when the output grating interface is a Si3N4 / buffer layer grating structure, and the dielectric grating structure is a two-dimensional grating structure, the two-dimensional grating structure is a dielectric grating structure of a non-axisymmetric periodic unit, and the non-axisymmetric periodic unit refers to a long period and a short period in two periodic directions of the two-dimensional grating along the axis of the incident light, and for each of the periodic units, the long period / short period ≥ 2 / 1; the angle between the two periodic directions ≥ 45°.

[0011] Preferably, the grating period of the dielectric grating structure is 0.1 to 10 times of the response wavelength, the duty cycle is 0.2 to 0.8, and the grating height is 0.02 to 1 μm.

[0012] Preferably, along the light incident direction, the grating layer includes a Si3N4 optical film and a Si3N4 / buffer layer exit grating interface arranged in sequence;

[0013] Or the grating layer includes a SiO2 / Si3N4 incident grating interface and a Si3N4 optical film arranged in sequence;

[0014] Or the grating layer includes a SiO2 / Si3N4 incident grating interface, a Si3N4 optical film and a Si3N4 / buffer layer exit grating interface which are arranged in sequence.

[0015] Preferably, the thickness of the Si3N4 optical film is ≥30nm.

[0016] Preferably, the thickness of the buffer layer is 10 nm to 2 μm, and the p-type doping concentration of the buffer layer is 10 18 ~10 19 cm -3 ;

[0017] The doping concentration of the buffer layer remains unchanged, or decreases gradually from the body to the vacuum surface;

[0018] The material of the buffer layer includes GaAlAs, InGaAlAs or GaAlAsP;

[0019] When the material of the buffer layer is GaAlAs, the molar content of the Al component is 0.5-1, and the total molar amount of Ga and Al in the GaAlAs is 1;

[0020] When the material of the buffer layer is InGaAlAs, the molar content of the Al component is 0.5-1, the molar content of In is 0-0.2, and the total molar amount of In, Ga and Al in the InGaAlAs is 1;

[0021] When the material of the buffer layer is GaAlAsP, the molar content of the Al component is 0.5-1, the molar content of P is 0-0.5, the total molar amount of Ga and Al in the GaAlAsP is 1, and the total molar amount of As and P in the GaAlAsP is 1.

[0022] Preferably, the thickness of the emission layer is 0.3-2.5 μm, and the p-type doping concentration of the emission layer is 10 18 ~10 19 cm -3 ;

[0023] The doping concentration of the emission layer remains unchanged, or decreases gradually from the body to the vacuum surface;

[0024] The bandgap width of the emission layer is always smaller than the bandgap width of the buffer layer;

[0025] The material of the emission layer includes GaAs, InGaAs, AlGaAs or GaAsP, and the bandgap width of the emission layer remains unchanged or decreases gradually from the body to the vacuum surface;

[0026] When the material of the emission layer includes InGaAs, the molar content of In is 0 to 0.2, and the total molar amount of In and Ga in the InGaAs is 1;

[0027] When the material of the emission layer includes GaAlAs, the molar content of the Al component is 0 to 0.5, and the total molar amount of Ga and Al in the GaAlAs is 1;

[0028] When the material of the emission layer includes GaAsP, the molar content of P is 0-0.5, and the total molar amount of As and P in the GaAsP is 1.

[0029] The present invention also provides the application of the transmission type photocathode described in the above technical solution in the field of low-light-level night vision, the field of low-light-level remote sensing imaging or photomultiplier tubes.

[0030] The present invention provides a transmission-type GaAs-based photocathode, which includes a SiO2 layer, a grating layer, a buffer layer, an emission layer and an activation layer stacked in sequence along the light incident direction; the grating layer includes a Si3N4 optical film and a dielectric grating structure of non-axisymmetric periodic units; the dielectric grating structure is an incident grating interface and / or an exit grating interface. The present invention introduces a grating layer between the SiO2 layer and the photoelectric emission material, so that the signal light incident from the SiO2 layer to the grating layer enters the emission layer in the form of diffracted light, and the lateral transmission of the diffracted light increases the absorption distance of the light in the emission layer, thereby improving the light response, especially the long-wave threshold band with insufficient absorption. The working principle of the transmission-type GaAs-based photocathode of the present invention is that first, after the signal light passes through the SiO2 layer, it enters the grating layer and exits from the grating layer in the form of diffracted light (such as Figure 2 As shown), the diffracted light is transmitted in the buffer layer and the emission layer in the form of lateral transmission, and the signal light is absorbed in the emission layer; secondly, the diffracted light reaching the emission layer / vacuum interface, if the total reflection condition is met (such as Figure 2As shown), the signal light is fully reflected and the emission layer is absorbed twice, thereby achieving full absorption of the signal light, especially the long-wave threshold band with no absorption component; then, the signal light is absorbed by the emission layer and converted into photoelectrons, which cross to the emission layer / vacuum surface and are emitted to the vacuum with a certain probability; at the same time, for the long-wave threshold band with insufficient absorption, the near-axisymmetric periodic unit structure has a small non-axisymmetric characteristic (such as a square structure, the maximum ratio of its non-axisymmetric periodic unit, that is, the diagonal / side length is only 1.414 / 1), so the polarization response effect is always weak, and the grating layer of the cathode of the present invention has a large non-axisymmetric characteristic of long period / short period ≥ 2 / 1 (the one-dimensional grating itself has a non-axisymmetric structure), which can be based on actual application needs, so it can achieve a polarization response effect of a certain wavelength that is far better than the near-axisymmetric structure. Moreover, the grating structure in the grating layer can release the stress brought by the Si3N4 optical film, which is more conducive to the implementation of the manufacturing process. It should be particularly noted that, since the equivalent refractive index of the grating interface is between the refractive indices of the two materials that constitute the grating, when the dielectric grating structure is an incident grating interface and an exit grating interface, there are two grating interfaces at this time, then compared with a single grating interface, and an axisymmetric (circular) or near-axisymmetric (square, regular hexagon and other regular polygons, etc.) grating interface: first, the two grating structures are easier to obtain a better diffraction effect, thereby achieving a longer absorption path, thereby increasing the signal light absorption rate; secondly, from the SiO2 layer to the buffer layer, the refractive index transition of the material is smoother, and it is easier to reduce the reflectivity and increase the transmittance; then, the setting of the two grating interfaces, especially the setting of the non-axisymmetric periodic unit (long period / short period is not less than 2 / 1), is easier to achieve a higher polarization response effect at a certain wavelength in the long-wave threshold band, and the near-axisymmetric periodic unit structure is due to the near-axisymmetry. The setting results in a weak polarization effect that is far weaker than that of the cathode of the present invention (the axially symmetrical setting of the axially symmetrical periodic unit structure has no polarization response). Therefore, the setting of the two grating interfaces makes it easier to obtain a high absorption rate and a large polarization response at a certain wavelength (long-wave threshold band) based on application requirements, thereby achieving a higher response performance than the grating structure of the axially symmetrical periodic unit or the near-axially symmetrical periodic unit, and further expanding the application range of the cathode. Therefore, without increasing the thickness of the emission layer, the transmission-type GaAs-based photocathode of the present invention increases the propagation distance of light in the emission layer through the diffraction of signal light at the grating layer, improves the absorption of signal light, and can achieve a polarization response effect at a certain wavelength based on application requirements in the long-wave threshold band, thereby having a higher long-wave infrared response enhancement and even achieving polarization response performance, which is more conducive to detection and imaging applications in low-light level night vision in low illumination. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1It is a schematic structural diagram of the transmission-type GaAs-based photocathode of the present invention;

[0032] Figure 2 Schematic diagram of the structure and working principle of the transmission-type GaAs-based photocathode of the present invention when the grating layer is a Si3N4 / buffer layer grating structure (a rectangular grating is used as an example for explanation), wherein 1 is a SiO2 layer, 2 is a grating layer, 3 is a buffer layer, 4 is an emission layer, 5 is an activation layer, 6 is a buffer layer grating structure (a rectangular grating structure is used as an example in the figure), 7 is incident light, 8 is diffracted light, and 9 is diffracted light that satisfies total surface reflection;

[0033] Figure 3 The absorption spectra comparison diagram of the transmissive GaAs-based photocathode described in Example 1 and the traditional transmissive photocathode (a), and the 90° / 0° polarization extinction ratio diagram of the transmissive GaAs-based photocathode described in Example 1 (b);

[0034] Figure 4 A comparison diagram of the absorption spectra of the transmissive GaAs-based photocathode described in Example 2 and the conventional transmissive photocathode;

[0035] Figure 5 This is a comparison diagram of the absorption spectra of the transmissive GaAs-based photocathode described in Example 3 and the traditional transmissive photocathode;

[0036] Figure 6 The absorption spectra comparison diagram of the transmissive GaAs-based photocathode described in Example 4, the micro-nano transmissive GaAs cathode described in Comparative Example 1, and the traditional transmissive photocathode (a), and the 90° / 0° polarization extinction ratio diagram of the transmissive GaAs-based photocathode described in Example 4 (b);

[0037] Figure 7 The absorption spectra comparison diagram of the transmissive GaAs-based photocathode described in Example 5 and the micro-nano transmissive GaAs cathode described in Comparative Example 1 (a) and the 90° / 0° polarization extinction ratio diagram of the transmissive GaAs-based photocathode described in Example 4 (b) are shown. DETAILED DESCRIPTION

[0038] The present invention provides a transmissive GaAs-based photocathode, which comprises a SiO2 layer, a grating layer, a buffer layer, an emission layer and an activation layer stacked in sequence along the light incident direction;

[0039] The grating layer comprises a Si3N4 optical film and a dielectric grating structure of a non-axisymmetric periodic unit; the dielectric grating structure is an incident grating interface and / or an exit grating interface.

[0040] In the present invention, the non-axisymmetric periodic unit can be understood as each periodic unit of the dielectric grating; the non-axisymmetric periodic unit is not a near-axisymmetric periodic unit with weak symmetry, and the near-axisymmetric periodic unit means that the cross-section of each periodic unit is a regular polygon such as a square, a regular hexagon, and a near-axisymmetric structure based on a circle.

[0041] In the present invention, the SiO2 layer is preferably 7056 optical glass or 9741 transparent purple optical glass; the present invention has no special limitation on the thickness of the SiO2 layer, and a thickness well known to those skilled in the art may be used.

[0042] In the present invention, the incident grating interface is preferably a SiO2 / Si3N4 grating interface, and the exit grating interface is preferably a Si3N4 / buffer layer grating structure.

[0043] In the present invention, the dielectric grating structure is preferably a one-dimensional grating structure or a two-dimensional grating structure; the grating period of the dielectric grating structure is preferably 0.1 to 10 times the response wavelength, more preferably 0.2 to 6 times the response wavelength, and most preferably 0.25 to 3.5 times the response wavelength; the duty cycle is preferably 0.2 to 0.8, more preferably 0.4 to 0.6; the grating height is preferably 0.02 to 1 μm, more preferably 0.05 to 800 nm, and most preferably 0.2 to 0.6 μm.

[0044] In the present invention, when the output grating interface is a Si3N4 / buffer layer grating structure, and the dielectric grating structure is a two-dimensional grating structure, the two-dimensional grating structure is a dielectric grating structure of a non-axisymmetric periodic unit, and the non-axisymmetric periodic unit refers to a long period and a short period in two periodic directions of the two-dimensional grating along the axis of the incident light. For each of the non-axisymmetric periodic units, the long period / short period is preferably ≥ 2 / 1; the angle between the two periodic directions is preferably ≥ 45°, and more preferably 90°. In the present invention, the long period / short period is higher than that of a square, a regular hexagon, and a circle-based axially symmetrical periodic unit structure, and thus a higher polarization response effect can be obtained than that of the axially symmetrical periodic unit structure.

[0045] For example, for each periodic unit of the two-dimensional grating, that is, including the two periodic directions, the following examples are given: if the structure of the non-axisymmetric periodic unit is a rectangle, and each periodic unit is a rectangle, then the directions corresponding to the two sides of the rectangle are the two periodic directions, the long side length is the long period, and the short side length is the short period; if each periodic unit is an ellipse, then the major axis and the minor axis of the ellipse are the long period and the short period, respectively; other asymmetric periodic unit structures and the long and short periods can be deduced by analogy;

[0046] In the present invention, the arrangement of the non-axisymmetric periodic unit structure can not only enhance light absorption, but also realize polarization response of a certain wavelength in the long-wave threshold band, thereby further improving the detection and imaging performance of signal light.

[0047] In the present invention, the two-dimensional grating structure is a dielectric grating structure of a non-axisymmetric periodic unit, and the cross section of the grating structure of the dielectric grating structure of the non-axisymmetric periodic unit (the cross section along the normal direction of the growth surface) is a rectangular, triangular, trapezoidal or sinusoidal structure (rectangular structure such as Figure 2 shown).

[0048] In the present invention, the arrangement of the non-axisymmetric periodic unit and the non-axisymmetric one-dimensional grating structure itself can further achieve a certain polarization response effect in the long-wave threshold band based on enhanced absorption of incident light according to actual application requirements.

[0049] In the present invention, along the light incident direction, the grating layer preferably includes a Si3N4 optical film and an exit grating interface arranged in sequence (i.e., a Si3N4 optical film and a Si3N4 / buffer layer exit grating interface arranged in sequence); or the grating layer includes an incident grating interface and a Si3N4 optical film arranged in sequence (i.e., a SiO2 / Si3N4 incident grating interface and a Si3N4 optical film arranged in sequence); or the grating layer includes an incident grating interface, a Si3N4 optical film, and an exit grating interface arranged in sequence (i.e., a SiO2 / Si3N4 incident grating interface, a Si3N4 optical film, and a Si3N4 / buffer layer exit grating interface arranged in sequence). When the grating layer includes an incident grating interface and a Si3N4 optical film arranged in sequence, a SiO2 optical film is preferably included between the incident grating interface and the SiO2 layer. In the present invention, the SiO2 optical film plays an auxiliary bonding role between the SiO2 layer and the grating layer.

[0050] In the present invention, the function of the grating layer is to diffract the signal light incident on the grating layer, and emit the diffracted light to the emission layer. Due to the lateral scattering of the diffracted light, the average propagation distance of the diffracted light in the emission layer increases, and the light absorption rate increases; at the same time, when part of the diffracted light meets the total reflection condition at the exit surface of the vacuum interface, the part of the diffracted light can be totally reflected by the surface of the photocathode, re-enter the emission layer and be further absorbed. Therefore, without increasing the thickness of the absorption layer, the light absorption rate of the cathode is further increased, so that the quantum efficiency, especially the quantum efficiency in the long-wave threshold band, is further improved. At the same time, the grating layer arrangement of the present invention can also be designed as a non-axisymmetric periodic unit structure (the one-dimensional grating structure itself is a non-axisymmetric periodic unit structure), so that the polarization response required by the actual application can be achieved on the basis of enhancing light absorption according to the application requirements, especially in the long-wave threshold band.

[0051] In the present invention, the thickness of the Si3N4 optical film is preferably ≥30nm. In the present invention, the function of the Si3N4 optical film is to prevent impurities in the SiO2 layer from contaminating the buffer layer and the emission layer.

[0052] In the present invention, the thickness of the buffer layer is preferably 10 nm to 2 μm, and the p-type doping concentration of the buffer layer is preferably 10 18 ~10 19 cm -3 .

[0053] The doping concentration of the buffer layer is preferably unchanged, or is gradually reduced from the body to the vacuum surface, and the reduction gradient and range vary according to different practical applications.

[0054] In the present invention, the material of the buffer layer preferably includes GaAlAs, InGaAlAs or GaAlAsP;

[0055] When the material of the buffer layer is GaAlAs, the molar content of the Al component is preferably 0.5-1, and the total molar amount of Ga and Al in the GaAlAs is preferably 1;

[0056] When the material of the buffer layer is InGaAlAs, the molar content of the Al component is preferably 0.5-1, the molar content of In is preferably 0-0.2, and the total molar amount of In, Ga and Al in the InGaAlAs is preferably 1;

[0057] When the material of the buffer layer is GaAlAsP, the molar content of the Al component is preferably 0.5-1, the molar content of P is preferably 0-0.5, the total molar amount of Ga and Al in the GaAlAsP is preferably 1, and the total molar amount of As and P in the GaAlAsP is preferably 1.

[0058] In the present invention, the component contents of Al, In and P in the buffer layer remain unchanged along the light incident direction; the p-type doping concentration in the buffer layer remains unchanged along the light incident direction or gradually decreases along the light incident direction.

[0059] In the present invention, the function of the buffer layer is to block the diffusion of Si3N4 material to the emission layer, reduce the defects of the buffer layer / emission layer interface, reduce the loss of photoelectrons at the interface, and block the diffusion of photoelectrons toward the SiO2 layer.

[0060] In the present invention, the thickness of the emission layer is preferably 0.3 to 2.5 μm, and the p-type doping concentration of the emission layer is preferably 10 18 ~10 19 cm -3 .

[0061] The bandgap width of the emission layer is always smaller than the bandgap width of the buffer layer;

[0062] The doping concentration of the emission layer remains unchanged, or decreases gradually from the body to the vacuum surface, and the decreasing gradient and range vary according to different practical applications.

[0063] In the present invention, the material of the emission layer preferably includes GaAs, InGaAs, AlGaAs or GaAsP, and the bandgap width of the emission layer remains unchanged, or decreases gradually from the body to the vacuum surface;

[0064] When the material of the emission layer includes InGaAs, the molar content of In is preferably 0 to 0.2, and the total molar amount of In and Ga in the InGaAs is preferably 1;

[0065] When the material of the emission layer includes GaAlAs, the molar content of the Al component is preferably 0 to 0.5, and the total molar amount of Ga and Al in the GaAlAs is preferably 1;

[0066] When the material of the emission layer includes GaAsP, the molar content of P is preferably 0-0.5, and the total molar amount of As and P in the GaAsP is preferably 1.

[0067] In the present invention, along the direction of the incident light, the p-type doping concentration in the emission layer remains unchanged or gradually decreases from the inside of the emission layer to the emission layer / vacuum surface. The bandgap width of the emission layer remains unchanged or decreases gradually from the inside to the surface, and the reduction gradient varies depending on the actual application requirements. When the bandgap width of the emission layer changes, it is determined by the change in the content of the Al component, the In component, or the P component; the function of the emission layer is to absorb signal light and generate photoelectrons. Among them, the Al component content in the emission layer material is less than that in the buffer layer material; the In component content in the emission layer material is greater than or equal to that in the buffer layer material; the P component content in the emission layer material is less than or equal to that in the buffer layer material.

[0068] In the present invention, the thickness of the activation layer is preferably 0.5 to 1.5 nm; the material of the activation layer is preferably Cs:O activation layer, Cs:F activation layer, Cs:NF3 activation layer or Li:F activation layer.

[0069] In the present invention, when the grating layer preferably includes a Si3N4 optical film and an exit grating interface arranged in sequence, the method for preparing the transmission-type GaAs-based photocathode preferably includes the following steps:

[0070] A GaAs transition layer (0.5-1 micron), an etching barrier layer, an emission layer, a buffer layer, an output grating prefabricated layer and a GaAs protective layer are sequentially epitaxially grown on a GaAs substrate by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) semiconductor epitaxial technology, and then the GaAs protective layer is removed by chemical etching to expose the output grating prefabricated layer; wherein the material of the output grating prefabricated layer is the same as the interface material of the buffer layer;

[0071] By means of a known grating manufacturing process, one side of the surface of the exit grating prefabricated layer is etched into an air / exit grating prefabricated structure, and then Si3N4 material is uniformly deposited on the surface of the air / exit grating prefabricated structure, so that the Si3N4 material replaces the air in the air / exit grating prefabricated structure, and then the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, in addition to forming a grating structure interface, the remaining Si3N4 material on the side close to the SiO2 layer can also be regarded as a Si3N4 optical film, forming the grating layer of the present invention: Si3N4 optical film / exit grating interface, that is, Si3N4 optical film / Si3N4 buffer layer grating interface;

[0072] Depositing a layer of SiO2 optical film on the surface of the Si3N4 optical film in the grating layer;

[0073] After the light-emitting side of the SiO2 layer is closely attached to the SiO2 optical film, the grating layer and the SiO2 layer are thermally bonded together under vacuum heating conditions by a known thermal bonding process for a transmission-type GaAs photocathode, and then the GaAs substrate and the etching barrier layer are removed in sequence by wet etching to expose the emission layer;

[0074] At vacuum degree ≤10 -7 Under ultra-high vacuum conditions of 1.5 Pa, an activation layer is deposited on the surface of the emission layer to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode.

[0075] The present invention does not have any special limitation on the process of metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), and the process well known to those skilled in the art can be used. The present invention does not have any special limitation on the process of chemical etching, and the process well known to those skilled in the art can be used. The present invention does not have any special limitation on the thermal bonding process, and the process well known to those skilled in the art can be used. In the present invention, the grating manufacturing processes are all well-known processes, and the present invention does not have any special limitation on the grating manufacturing processes, and the process well known to those skilled in the art can be used.

[0076] In the present invention, the thickness of the GaAs transition layer is preferably 0.5 to 1 μm, more preferably 0.2 to 3 μm, further preferably 0.3 to 2 μm, and most preferably 0.5 to 1 μm.

[0077] In the present invention, the material of the corrosion barrier layer is preferably Ga 0.5 Al 0.5 As; The thickness of the corrosion barrier layer is preferably 0.5 to 5 μm, more preferably 1 to 3 μm, and most preferably 1.5 to 2.5 μm.

[0078] In the present invention, the thickness of the grating prefabricated layer is preferably ≥30 nm, more preferably 30 to 2000 nm, and most preferably 50 to 700 nm; the material of the grating prefabricated layer is preferably the same as that of the buffer layer.

[0079] In the present invention, the thickness of the GaAs protective layer is preferably 30 to 1500 nm, more preferably 50 to 1000 nm, and most preferably 100 to 500 nm.

[0080] In the present invention, when the grating layer preferably includes an incident grating interface and a Si3N4 optical film arranged in sequence, the method for preparing the transmission-type GaAs-based photocathode preferably includes the following steps:

[0081] By using MOCVD or MBE semiconductor epitaxial technology, a GaAs transition layer (0.5-1 micron), an etching barrier layer, an emission layer 4, a buffer layer 3 and a GaAs protective layer are epitaxially grown in sequence on a GaAs substrate, and then the GaAs protective layer is removed by chemical etching to expose the buffer layer 3.

[0082] The present invention deposits a Si3N4 film with an optically uniform thickness on the surface of the buffer layer 3. The Si3N4 film is divided into two parts, the Si3N4 optical film on the inner side, and the Si3N4 grating prefabricated layer on the air side. The Si3N4 grating prefabricated layer is made into an incident grating / air prefabricated structure by a known grating manufacturing process; then, SiO2 material is uniformly deposited on the surface of the incident grating / air prefabricated structure, so that the SiO2 material replaces the air in the incident grating / air prefabricated structure, and then, the excess SiO2 material on the surface is removed by mechanical polishing, and the SiO2 surface is polished into an optical surface to form the grating layer of the present invention: incident grating interface / Si3N4 optical film, that is, SiO2 / Si3N4 grating interface / Si3N4 optical film.

[0083] The present invention does not have any special limitation on the etching process, and the etching process may be performed using a process well known to those skilled in the art.

[0084] After obtaining the grating layer, the present invention deposits a layer of SiO2 optical film on the surface of the grating layer. The present invention does not have any special limitation on the deposition process, and the process well known to those skilled in the art can be used.

[0085] After obtaining the SiO2 optical film, the present invention closely adheres the light emitting side of the SiO2 layer to the SiO2 optical film, and then uses the well-known thermal bonding process of the transmission GaAs photocathode to bond the grating layer to the SiO2 layer under vacuum heating conditions, and then uses wet etching to sequentially remove the GaAs substrate and the etching barrier layer to expose the emission layer.

[0086] The present invention does not have any special limitation on the MOCVD or MBE process, and the process well known to those skilled in the art can be used. The present invention does not have any special limitation on the chemical etching process, and the process well known to those skilled in the art can be used. The present invention does not have any special limitation on the thermal bonding process, and the process well known to those skilled in the art can be used. In the present invention, the grating manufacturing processes are all well-known processes, and the present invention does not have any special limitation on the grating manufacturing processes, and the process well known to those skilled in the art can be used.

[0087] Finally, at a vacuum degree of ≤10 -7Under ultra-high vacuum conditions of 1.5 Pa, an activation layer is deposited on the surface of the emission layer to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode. The present invention has no special limitation on the deposition process of the activation layer, and a process well known to those skilled in the art can be used.

[0088] When the grating layer includes an incident grating interface, a Si3N4 optical film and an exit grating interface arranged in sequence, the method for preparing the transmission-type GaAs-based photocathode preferably includes the following steps:

[0089] By using metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) semiconductor epitaxial technology, a GaAs transition layer (0.5-1 micron), an etching barrier layer, an emission layer 4, a buffer layer 3, an output grating prefabricated layer and a GaAs protective layer are sequentially epitaxially grown on a GaAs substrate, and then the GaAs protective layer is removed by chemical etching to expose the output grating prefabricated layer. The material of the output grating prefabricated layer is the same as the interface material of the buffer layer;

[0090] By means of a known grating manufacturing process, one side of the surface of the exit grating prefabricated layer is etched into an air / exit grating prefabricated structure, and then Si3N4 material is uniformly deposited on the surface of the air / exit grating prefabricated structure, so that the Si3N4 material replaces the air in the air / exit grating prefabricated structure, and then the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, in addition to forming a grating structure interface, the remaining Si3N4 material on the side close to the SiO2 layer can also be regarded as a Si3N4 optical film, forming the grating layer of the present invention: Si3N4 optical film / exit grating interface, that is, Si3N4 optical film / Si3N4 buffer layer grating interface; in the present invention, the process is the same as the preparation process when the grating layer includes a Si3N4 optical film and an exit grating interface arranged in sequence, and will not be repeated here.

[0091] The present invention deposits another layer of the Si3N4 grating prefabricated layer on the surface of the Si3N4 optical film. The Si3N4 grating prefabricated layer is made into an incident grating / air prefabricated structure through a known grating manufacturing process; then, SiO2 material is uniformly deposited on the surface of the incident grating / air prefabricated structure, so that the SiO2 material replaces the air in the incident grating / air prefabricated structure, and then, the excess SiO2 material on the surface is removed through mechanical polishing, and the SiO2 surface is polished into an optical surface to form the grating layer of the present invention: incident grating interface / Si3N4 optical film, that is, SiO2 / Si3N4 grating interface / Si3N4 optical film. In the present invention, the process is the same as when the grating layer preferably includes an incident grating interface and a Si3N4 optical film arranged in sequence, and will not be repeated here.

[0092] Through the above process, the grating layer is obtained: incident grating interface / Si3N4 optical film / Si3N4 buffer layer grating interface;

[0093] After obtaining the grating layer, the present invention deposits a layer of SiO2 optical film on the surface of the grating layer. The present invention does not have any special limitation on the deposition process, and the process well known to those skilled in the art can be used.

[0094] After obtaining the SiO2 optical film, the present invention closely adheres the light emitting side of the SiO2 layer to the SiO2 optical film, and then uses the well-known thermal bonding process of the transmission GaAs photocathode to bond the grating layer to the SiO2 layer under vacuum heating conditions, and then uses wet etching to sequentially remove the GaAs substrate and the etching barrier layer to expose the emission layer.

[0095] The present invention does not have any special limitation on the MOCVD or MBE process, and the process well known to those skilled in the art can be used. The present invention does not have any special limitation on the chemical etching process, and the process well known to those skilled in the art can be used. The present invention does not have any special limitation on the thermal bonding process, and the process well known to those skilled in the art can be used. In the present invention, the grating manufacturing processes are all well-known processes, and the present invention does not have any special limitation on the grating manufacturing processes, and the process well known to those skilled in the art can be used.

[0096] Finally, at a vacuum degree of ≤10 -7 Under ultra-high vacuum conditions of 1.5 Pa, an activation layer is deposited on the surface of the emission layer to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode. The present invention has no special limitation on the deposition process of the activation layer, and a process well known to those skilled in the art can be used.

[0097] In the present invention, the above-mentioned preparation process preferably refers to the process described in the above-mentioned technical solution, and will not be described in detail here.

[0098] The present invention also provides the application of the transmission photocathode described in the above technical solution in the field of low-light-level night vision, low-light-level remote sensing imaging or photomultiplier tube. The present invention has no special limitation on the application method, and the application method can be carried out by methods well known to those skilled in the art.

[0099] The transmissive GaAs-based photocathode provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0100] Example 1

[0101] like Figure 1 As shown: the transmissive GaAs-based photocathode comprises a SiO2 layer 1, a grating layer 2, a buffer layer 3, an emission layer 4 and an activation layer 5 which are stacked in sequence along the light incident direction;

[0102] The SiO2 layer 1 is a double-sided polished Corning 7056 borosilicate glass with a thickness of 2 cm;

[0103] The grating layer 2 includes a Si3N4 optical film (thickness of 50nm) and a Si3N4 / Ga2O3 film stacked in sequence along the light incident direction. 0.1 Al 0.9 As one-dimensional rectangular grating structure (period is 850nm, Si3N4 / Ga 0.1 Al 0.9 The duty cycle of As is 1:1 and the grating height is 450nm);

[0104] The buffer layer 3 has a thickness of 50 nm and a p-type doping concentration of 10 19 cm -3 Ga 0.1 Al 0.9 As buffer layer;

[0105] The emission layer 4 has a thickness of 1.5 μm and a p-type doping concentration of 10 19 cm -3 GaAs emission layer;

[0106] The activation layer 5 is a Cs:O activation layer with a thickness of 1 nm;

[0107] The preparation method of the transmission-type GaAs-based photocathode:

[0108] 1) Using MOCVD technology, GaAs with a thickness of 2 μm is deposited on the GaAs substrate. 0.5 Al 0.5As corrosion barrier layer, GaAs emission layer 4 with a thickness of 1.5 μm, GaAs with a thickness of 50 nm 0.1 Al 0.9 As buffer layer 3, Ga with a thickness of 450nm 0.1 Al 0.9 As grating prefabricated layer and GaAs protective layer with a thickness of 0.5 μm, and then remove the GaAs protective layer with a thickness of 0.5 μm by chemical etching to expose the GaAs with a thickness of 450 nm. 0.1 Al 0.9 As grating prefabricated layer;

[0109] 2) The Ga with a thickness of 450 nm 0.1 Al 0.9 The surface of the As grating prefabricated layer is etched into Ga 0.1 Al 0.9 After the As / air grating is prefabricated, the Ga 0.1 Al 0.9 As / air grating prefabricated structure surface is uniformly deposited with Si3N4 material (the Si3N4 material replaces the Ga 0.1 Al 0.9 As / air grating prefabricated structure), the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, the Si3N4 material is removed from the Si3N4 / Ga 0.1 Al 0.9 As rectangular grating structure interface, on the side close to the SiO2 layer, the remaining Si3N4 material can also be regarded as a Si3N4 optical film with uniform thickness and a thickness of 50 nanometers, that is, the Si3N4 optical film with a thickness of 50nm of the photocathode of the present invention, forming the grating layer 2 of the present invention: Si3N4 optical film (50nm) / Si3N4 / Ga 0.1 Al 0.9 As grating structure (450nm);

[0110] 3) depositing a SiO2 optical film with a thickness of about 100 nm on the surface of the Si3N4 optical film in the grating layer 2;

[0111] 4) After the light emitting side of the SiO2 layer 1 is closely attached to the SiO2 optical film, the grating layer 2 is bonded to the SiO2 layer 1 under vacuum heating conditions, and then the GaAs substrate, the GaAs layer with a thickness of 2 μm, and the GaAs layer with a thickness of 2 μm are removed in sequence by wet etching. 0.5 Al 0.5 As corrosion barrier layer and GaAs emission layer 4 with a thickness of 1.5 μm;

[0112] 5) In vacuum degree ≤10 -7 Under ultra-high vacuum conditions of 1.5 μm, a Cs:O activation layer 5 is deposited on the surface of the GaAs emission layer 4 with a thickness of 1.5 μm to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode;

[0113] Figure 3 The transmissive GaAs-based photocathode of the present invention and the conventional transmissive photocathode (SiO2 layer (2 cm) / Si3N4 antireflection film (100 nm) / GaAs-based photocathode in the incident light direction) are shown in FIG. 0.1 Al 0.9 A buffer layer (200nm) / GaAs emission layer (1500nm) / Cs:O activation layer (1nm)) absorption spectrum comparison diagram (a), and the 90° / 0° polarization extinction ratio diagram of the transmission-type GaAs-based photocathode of the present invention (b), where 0° refers to the direction along the one-dimensional grating period, and 90° refers to the direction perpendicular to the one-dimensional grating period. Figure 3 It can be seen that due to the introduction of the grating layer 2, the propagation distance of the signal light in the emission layer 4 is greatly increased, which leads to a significant increase in the absorption rate in the long-wave threshold band. Typically, the absorption rate at 900 nanometers reaches 70%, which is far higher than the traditional photocathode; at the same time, the 0° / 90° polarization extinction ratio at 900 nanometers is greater than 2, and the 90° / 0° polarization extinction ratio at 900 nanometers is greater than 25, indicating that the present invention can achieve a high polarization response of a certain wavelength in the long-wave threshold band. Therefore, the quantum efficiency and spectral sensitivity of the photocathode of the present invention are greatly increased, and a polarization response effect of a certain wavelength can be achieved in the long-wave threshold band, thereby further improving the cathode response performance.

[0114] Example 2

[0115] like Figure 1 As shown: the transmissive GaAs-based photocathode comprises a SiO2 layer 1, a grating layer 2, a buffer layer 3, an emission layer 4 and an activation layer 5 which are stacked in sequence along the light incident direction;

[0116] The SiO2 layer 1 is a double-sided polished Corning 7056 borosilicate glass with a thickness of 2 cm;

[0117] The grating layer 2 includes a SiO2 / Si3N4 rectangular grating structure (period is 770nm, the duty ratio of SiO2 / Si3N4 is 1:1, and the grating height is 50nm), a Si3N4 optical film (thickness is 50nm) and a Si3N4 / GaN4 film (thickness is 50nm) stacked in sequence along the light incident direction. 0.1 Al 0.9 As one-dimensional rectangular grating structure (period is 760nm, Si3N4 / Ga 0.1 Al 0.9The duty cycle of As is 1:1 and the grating height is 450nm);

[0118] The buffer layer 3 has a thickness of 100 nm and a p-type doping concentration of 10 19 cm -3 Ga 0.1 Al 0.9 As buffer layer;

[0119] The emission layer 4 has a thickness of 1.5 μm and a p-type doping concentration of 10 19 cm -3 GaAs emission layer;

[0120] The activation layer 5 is a Cs:O activation layer with a thickness of 1 nm;

[0121] The preparation method of the transmission-type GaAs-based photocathode:

[0122] 1) Using MOCVD technology, GaAs with a thickness of 2 μm is deposited on the GaAs substrate. 0.5 Al 0.5 As corrosion barrier layer, GaAs emission layer 4 with a thickness of 1.5 μm, GaAs with a thickness of 50 nm 0.1 Al 0.9 As buffer layer 3, Ga with a thickness of 450nm 0.1 Al 0.9 As grating prefabricated layer and GaAs protective layer with a thickness of 0.5 μm, and then remove the GaAs protective layer with a thickness of 0.5 μm by chemical etching to expose the GaAs with a thickness of 450 nm. 0.1 Al 0.9 As grating prefabricated layer;

[0123] 2) The Ga with a thickness of 450 nm 0.1 Al 0.9 The surface of the As grating prefabricated layer is etched into Ga 0.1 Al 0.9 After the As / air grating is prefabricated, the Ga 0.1 Al 0.9 As / air grating prefabricated structure surface is uniformly deposited with Si3N4 material (the Si3N4 material replaces the Ga 0.1 Al 0.9 As / air grating prefabricated structure), the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, the Si3N4 material is removed from the Si3N4 / Ga 0.1 Al 0.9As the rectangular grating structure interface, on the side close to the SiO2 layer, the remaining Si3N4 material can also be regarded as a Si3N4 optical film with uniform thickness and a thickness of 50 nanometers, that is, the Si3N4 optical film with a thickness of 50nm of the photocathode of the present invention, and the Si3N4 optical film is continuously deposited on the surface of the Si3N4 optical film with a thickness of 50nm, and a Si3N4 rectangular grating prefabricated layer with a thickness of 50nm is formed on the surface of the Si3N4 optical film with a thickness of 50nm;

[0124] 3) etching the surface of the Si3N4 rectangular grating prefabricated layer with a thickness of 50nm into a Si3N4 / air grating prefabricated structure; uniformly depositing SiO2 on the Si3N4 / air grating prefabricated structure to form a SiO2 / Si3N4 rectangular grating structure, forming the grating layer 2: SiO2 / Si3N4 grating structure (50nm) / Si3N4 optical film (50nm) / Si3N4 / Ga 0.1 Al 0.9 As grating structure (450nm); then through mechanical polishing, the surface of the SiO2 / Si3N4 rectangular grating structure is polished into an optical surface, and the remaining SiO2 forms a layer of SiO2 optical film with a thickness of 100nm (the auxiliary bonding effect between the SiO2 layer and the grating layer);

[0125] 4) After the light emitting side of the SiO2 layer 1 is closely attached to the SiO2 optical film, the grating layer 2 is bonded to the SiO2 layer 1 under vacuum heating conditions, and then the GaAs substrate, the GaAs layer with a thickness of 2 μm, and the GaAs layer with a thickness of 2 μm are removed in sequence by wet etching. 0.5 Al 0.5 As corrosion barrier layer and GaAs emission layer 4 with a thickness of 1.5 μm;

[0126] 5) In vacuum degree ≤10 -7 Under ultra-high vacuum conditions of 1.5 μm, a Cs:O activation layer 5 is deposited on the surface of the GaAs emission layer 4 with a thickness of 1.5 μm to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode;

[0127] Figure 4 The transmissive GaAs-based photocathode of the present invention (corresponding to 2. cathode of the present invention in the figure) and the conventional transmissive photocathode (SiO2 layer (2cm) / Si3N4 antireflection film (100nm) / GaAs-based photocathode in the incident light direction) are shown in FIG. 0.1 Al 0.9 A buffer layer (200nm) / GaAs emission layer (1500nm) / Cs:O activation layer (1nm), corresponding to the absorption spectrum comparison diagram of 1. Conventional cathode in the figure, by Figure 4 It can be seen that due to the introduction of the grating layer 2, the propagation distance of the signal light in the emission layer 4 is greatly increased, thereby greatly increasing the absorption rate of the long-wave threshold band, and the absorption rate of the light band and the threshold band can exceed that of the traditional cathode. Typically, the absorption rate at 900nm reaches 60%, which is far higher than that of the traditional photocathode. Therefore, the quantum efficiency and spectral sensitivity of the photocathode of the present invention are greatly increased, and the cathode response performance is further improved.

[0128] Example 3

[0129] like Figure 1 As shown: the transmissive GaAs-based photocathode comprises a SiO2 layer 1, a grating layer 2, a buffer layer 3, an emission layer 4 and an activation layer 5 which are stacked in sequence along the light incident direction;

[0130] The SiO2 layer 1 is a double-sided polished Corning 7056 borosilicate glass with a thickness of 2 cm;

[0131] The grating layer 2 includes a Si3N4 optical film (thickness of 50nm) and a Si3N4 / Ga2O3 film stacked in sequence along the light incident direction. 0.1 Al 0.9 As sinusoidal grating structure (period is 700nm, Si3N4 / Ga 0.1 Al 0.9 The duty cycle of As is 1:1 and the grating height is 300nm);

[0132] The buffer layer 3 has a thickness of 50 nm and a p-type doping concentration of 10 19 cm -3 Ga 0.1 Al 0.9 As buffer layer;

[0133] The emission layer 4 has a thickness of 1.5 μm and a p-type doping concentration of 10 19 cm -3 GaAs emission layer;

[0134] The activation layer 5 is a Cs:O activation layer with a thickness of 1 nm;

[0135] The preparation method of the transmission-type GaAs-based photocathode:

[0136] 1) Using MOCVD technology, GaAs with a thickness of 2 μm is deposited on the GaAs substrate. 0.5 Al 0.5 As corrosion barrier layer, GaAs emission layer 4 with a thickness of 1.5 μm, GaAs with a thickness of 50 nm 0.1 Al 0.9 As buffer layer 3, Ga with a thickness of 300nm 0.1 Al0.9 As grating prefabricated layer and GaAs protective layer with a thickness of 0.5 μm, and then remove the GaAs protective layer with a thickness of 0.5 μm by chemical etching to expose the GaAs with a thickness of 300 nm. 0.1 Al 0.9 As grating prefabricated layer;

[0137] 2) The Ga with a thickness of 300 nm 0.1 Al 0.9 The surface of the As grating prefabricated layer is etched into Ga 0.1 Al 0.9 After the As / air grating is prefabricated, the Ga 0.1 Al 0.9 As / air grating prefabricated structure surface is uniformly deposited with Si3N4 material (the Si3N4 material replaces the Ga 0.1 Al 0.9 As / air grating prefabricated structure), the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, the Si3N4 material is removed from the Si3N4 / Ga 0.1 Al 0.9 As rectangular grating structure interface, on the side close to the SiO2 layer, the remaining Si3N4 material can also be regarded as a Si3N4 optical film with uniform thickness and a thickness of 50 nanometers, that is, the Si3N4 optical film with a thickness of 50nm of the photocathode of the present invention, forming the grating layer 2 of the present invention: Si3N4 optical film (50nm) / Si3N4 / Ga 0.1 Al 0.9 As grating structure (300nm);

[0138] 3) depositing a SiO2 optical film with a thickness of about 100 nm on the surface of the Si3N4 optical film in the grating layer 2;

[0139] 4) After the light emitting side of the SiO2 layer 1 is closely attached to the SiO2 optical film, the grating layer 2 is bonded to the SiO2 layer 1 under vacuum heating conditions, and then the GaAs substrate, the GaAs layer with a thickness of 2 μm, and the GaAs layer with a thickness of 2 μm are removed in sequence by wet etching. 0.5 Al 0.5 As corrosion barrier layer and GaAs emission layer 4 with a thickness of 1.5 μm;

[0140] 5) In vacuum degree ≤10 -7Under ultra-high vacuum conditions of 1.5 μm, a Cs:O activation layer 5 is deposited on the surface of the GaAs emission layer 4 with a thickness of 1.5 μm to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode;

[0141] Figure 5 The transmissive GaAs-based photocathode of the present invention (corresponding to 2. cathode of the present invention in the figure) and the conventional transmissive photocathode (SiO2 layer (2cm) / Si3N4 antireflection film (100nm) / GaAs-based photocathode in the incident light direction) are shown in FIG. 0.1 Al 0.9 A buffer layer (200nm) / GaAs emission layer (1500nm) / Cs:O activation layer (1nm), corresponding to the absorption spectrum comparison diagram of 1. Conventional cathode in the figure, by Figure 5 It can be seen that due to the introduction of the grating layer 2, the propagation distance of the signal light in the emission layer 4 is greatly increased, so the absorption rate in the visible light band and the threshold band exceeds that of the traditional cathode. Typically, the absorption rate at 900nm reaches more than 40%. Therefore, the quantum efficiency and spectral sensitivity of the photocathode of the present invention are greatly increased, and the cathode response performance is further improved.

[0142] Example 4

[0143] like Figure 1 As shown: the transmissive GaAs-based photocathode comprises a SiO2 layer 1, a grating layer 2, a buffer layer 3, an emission layer 4 and an activation layer 5 which are stacked in sequence along the light incident direction;

[0144] The SiO2 layer 1 is a double-sided polished Corning 7056 borosilicate glass with a thickness of 2 cm;

[0145] The grating layer 2 includes a SiO2 / Si3N4 rectangular grating structure (with a period of 830nm, a SiO2 / Si3N4 duty ratio of 1:1, and a grating height of 200nm), a Si3N4 optical film (with a thickness of 100nm), and a Si3N4 / GaN4 film stacked in sequence along the light incident direction. 0.3 Al 0.7 As one-dimensional rectangular grating structure (period is 830nm, Si3N4 / Ga 0.3 Al 0.7 The duty cycle of As is 1:1 and the grating height is 500nm);

[0146] The buffer layer 3 has a thickness of 100 nm and a p-type doping concentration of 10 19 cm -3 Ga 0.3 Al 0.7 As buffer layer;

[0147] The emission layer 4 has a thickness of 800 nm and a p-type doping concentration of 10 19 cm -3 GaAs emission layer;

[0148] The activation layer 5 is a Cs:O activation layer with a thickness of 1 nm;

[0149] The preparation method of the transmission-type GaAs-based photocathode is shown in Example 2:

[0150] 1) Using MOCVD technology, GaAs with a thickness of 2 μm is deposited on the GaAs substrate. 0.5 Al 0.5 As corrosion barrier layer, GaAs emission layer 4 with a thickness of 800nm, Ga 0.3 Al 0.7 As buffer layer 3, Ga with a thickness of 500nm 0.3 Al 0.7 As grating prefabricated layer and GaAs protective layer with a thickness of 500nm, and then remove the GaAs protective layer with a thickness of 500nm by chemical etching to expose the GaAs 0.3 Al 0.7 As grating prefabricated layer;

[0151] 2) The Ga with a thickness of 500 nm 0.3 Al 0.7 The surface of the As grating prefabricated layer is etched into Ga 0.3 Al 0.7 After the As / air grating is prefabricated, the Ga 0.3 Al 0.7 As / air grating prefabricated structure surface is uniformly deposited with Si3N4 material (the Si3N4 material replaces the Ga 0.3 Al 0.7 As / air grating prefabricated structure), the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, the Si3N4 material is removed from the Si3N4 / Ga 0.3 Al 0.7 As the rectangular grating structure interface, on the side close to the SiO2 layer, the remaining Si3N4 material can also be regarded as a Si3N4 optical film with uniform thickness and a thickness of 100 nanometers, that is, the Si3N4 optical film with a thickness of 100 nm of the photocathode of the present invention, and the Si3N4 optical film is continuously deposited on the surface of the Si3N4 optical film with a thickness of 100 nm, and a Si3N4 rectangular grating prefabricated layer with a thickness of 200 nm is formed on the surface of the Si3N4 optical film with a thickness of 200 nm;

[0152] 3) etching the surface of the Si3N4 rectangular grating prefabricated layer with a thickness of 200nm into a Si3N4 / air grating prefabricated structure; uniformly depositing SiO2 on the Si3N4 / air grating prefabricated structure to form a SiO2 / Si3N4 rectangular grating structure, forming the grating layer 2: SiO2 / Si3N4 grating structure (200nm) / Si3N4 optical film (100nm) / Si3N4 / Ga 0.3 Al 0.7 As / As grating structure (500nm); then, through mechanical polishing, the surface of the SiO2 / Si3N4 rectangular grating structure is polished into an optical surface, and the remaining SiO2 forms a layer of SiO2 optical film with a thickness of 100nm (the auxiliary bonding effect between the SiO2 layer and the grating layer);

[0153] 4) After the light emitting side of the SiO2 layer 1 is closely attached to the SiO2 optical film, the grating layer 2 is bonded to the SiO2 layer 1 under vacuum heating conditions, and then the GaAs substrate, the GaAs layer with a thickness of 2 μm, and the GaAs layer with a thickness of 2 μm are removed in sequence by wet etching. 0.5 Al 0.5 As corrosion barrier layer and GaAs emission layer 4 with a thickness of 800nm;

[0154] 5) In vacuum degree ≤10 -7 Under ultra-high vacuum conditions of 1.5 Pa, a Cs:O activation layer 5 is deposited on the surface of the GaAs emission layer 4 with a thickness of 800 nm to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode.

[0155] Example 5

[0156] The grating layer 2 includes a SiO2 / Si3N4 rectangular grating structure (with a period of 900nm, a SiO2 / Si3N4 duty ratio of 1:1, and a grating height of 200nm), a Si3N4 optical film (with a thickness of 100nm), and a Si3N4 / GaN4 film stacked in sequence along the light incident direction. 0.3 Al 0.7 As rectangular grating structure (period is 900nm, Si3N4 / Ga 0.3 Al 0.7 The duty cycle of As is 1:1 and the grating height is 450nm);

[0157] The buffer layer 3 has a thickness of 200 nm and a p-type doping concentration of 10 19 cm -3 Ga 0.3 Al 0.7 As buffer layer;

[0158] The rest is as shown in Example 4.

[0159] The preparation method of the transmissive GaAs-based photocathode is shown in Example 4:

[0160] 1) Using MOCVD technology, GaAs with a thickness of 2 μm is deposited on the GaAs substrate. 0.5 Al 0.5 As corrosion barrier layer, GaAs emission layer 4 with a thickness of 800nm, Ga 0.3 Al 0.7 As buffer layer 3, Ga with a thickness of 500nm 0.3 Al 0.7 As grating prefabricated layer and GaAs protective layer with a thickness of 500nm, and then remove the GaAs protective layer with a thickness of 500nm by chemical etching to expose the GaAs with a thickness of 450nm. 0.3 Al 0.7 As grating prefabricated layer;

[0161] 2) The Ga with a thickness of 450 nm 0.3 Al 0.7 The surface of the As grating prefabricated layer is etched into Ga 0.3 Al 0.7 After the As / air grating is prefabricated, the Ga 0.3 Al 0.7 As / air grating prefabricated structure surface is uniformly deposited with Si3N4 material (the Si3N4 material replaces the Ga 0.3 Al 0.7 As / air grating prefabricated structure), the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, the Si3N4 material is removed from the Si3N4 / Ga 0.3 Al 0.7 As the rectangular grating structure interface, on the side close to the SiO2 layer, the remaining Si3N4 material can also be regarded as a Si3N4 optical film with uniform thickness and a thickness of 100 nanometers, that is, the Si3N4 optical film with a thickness of 100 nm of the photocathode of the present invention, and the Si3N4 optical film is continuously deposited on the surface of the Si3N4 optical film with a thickness of 100 nm, and a Si3N4 rectangular grating prefabricated layer with a thickness of 200 nm is formed on the surface of the Si3N4 optical film with a thickness of 200 nm;

[0162] 3) etching the surface of the Si3N4 rectangular grating prefabricated layer with a thickness of 200nm into a Si3N4 / air grating prefabricated structure; uniformly depositing SiO2 on the Si3N4 / air grating prefabricated structure to form a SiO2 / Si3N4 rectangular grating structure, forming the grating layer 2: SiO2 / Si3N4 grating structure (200nm) / Si3N4 optical film (100nm) / Si3N4 / Ga 0.3 Al 0.7 As / As grating structure (450nm); then, through mechanical polishing, the surface of the SiO2 / Si3N4 rectangular grating structure is polished into an optical surface, and the remaining SiO2 forms a layer of SiO2 optical film with a thickness of 100nm (the auxiliary bonding effect between the SiO2 layer and the grating layer);

[0163] The rest is as shown in Example 4.

[0164] Comparative Example 1

[0165] Transmissive GaAs photocathode based on cylindrical Wiener array, glass window / axisymmetric GaAs photocathode along the incident light direction 0.3 Al 0.7 As / Si3N4 / micro-nano array / GaAs emission layer / Cs:O activation layer;

[0166] Glass window: 7056 optical glass, thickness 2cm;

[0167] Si3N4: optical thin film, 200nm;

[0168] Axisymmetric micro-nano array: p-type Ga 0.3 Al 0.7 As / Si3N4 cylindrical micro-nanostructure array, period 500nm, cylindrical p-type Ga 0.3 Al 0.7 As height 500nm, diameter 300nm, p-type doping concentration 10 19 cm -3 , the other material of the axisymmetric micro-nano array is Si3N4;

[0169] GaAs emitter layer: p-type doping concentration 10 19 cm -3 , thickness 800nm.

[0170] Figure 6 The transmissive GaAs-based photocathode described in Example 4 of the present invention and the micro-nanostructured transmissive GaAs cathode described in Comparative Example 1, the conventional GaAs transmissive photocathode (glass window (2 cm) / Si3N4 antireflection film (100 nm) / GaAs in the incident light direction) are shown in FIG. 0.3 Al0.7 A buffer layer (200nm) / GaAs emission layer (800nm) / Cs:O activation layer (1nm), corresponding to the conventional cathode in the figure) absorption spectrum comparison diagram (a), the transmission GaAs-based photocathode 90° / 0° polarization extinction ratio diagram of this embodiment (b). Figure 6 It can be seen that the photocathodes of Example 4 and Comparative Example 1, due to the introduction of the grating layer 2 and the Wiener array respectively, realize the lateral diffraction of the signal light, so that the absorption of the signal light is significantly enhanced, especially in the long-wave band, so compared with the traditional transmission GaAs photocathode, the response performance is greatly improved; and the cathode of the present invention, due to the introduction of the grating layer 2, greatly enhances the infrared band response, so that the overall absorptivity of the cathode of the present invention is higher than that of the comparative micro-nano transmission GaAs cathode, especially, in the long-wave threshold band such as 900-950nm, the absorptivity of the cathode of the present embodiment far exceeds that of the traditional photocathode and the micro-nano transmission GaAs cathode; at the same time, the polarization extinction ratio of 900nm is close to 5, and the polarization extinction ratio of 925nm reaches 40. Therefore, the photocathode of the present invention has more excellent response characteristics, and its response performance is further improved compared with the traditional cathode and the comparative cathode.

[0171] Figure 7 The absorption spectra comparison diagram of the transmissive GaAs-based photocathode described in Example 5 of the present invention and the micro-nano transmissive GaAs cathode described in Comparative Example 1 (a) and the 90° / 0° polarization extinction ratio diagram of the transmissive GaAs-based photocathode described in this embodiment (b) are shown. Figure 7 It can be seen that due to the introduction of the grating layer 2, the infrared band response is greatly enhanced, so that the overall absorptivity of the cathode of the present invention is higher than that of the comparative micro-nano transmission-type GaAs cathode. In particular, in the long-wave threshold band of 875-900nm, the absorptivity of the cathode of this embodiment far exceeds that of the traditional photocathode and the micro-nano transmission-type GaAs cathode. At the same time, the polarization extinction ratios of 825nm and 875nm are close to 2, the polarization extinction ratio of 900nm reaches 2.7, and the polarization extinction ratio of 950nm reaches 2.2, with polarization extinction effects of multiple wavelengths. Therefore, the photocathode of the present invention has more excellent response characteristics, and its response performance is further improved compared with the comparative cathode.

[0172] Example 6

[0173] like Figure 1 As shown: the transmissive GaAs-based photocathode comprises a SiO2 layer 1, a grating layer 2, a buffer layer 3, an emission layer 4 and an activation layer 5 which are stacked in sequence along the light incident direction;

[0174] The SiO2 layer 1 is a double-sided polished Corning 7056 borosilicate glass with a thickness of 2 cm;

[0175] The grating layer 2 includes a Si3N4 optical film (thickness of 350nm) and a Si3N4 / Ga2O3 film stacked in sequence along the light incident direction. 0.3 Al 0.7 As two-dimensional rectangular grating structure (long period is 800nm, short period is 400nm, Si3N4 / Ga 0.3 Al 0.7 The duty cycle of As is 1:1 and the grating height is 350nm);

[0176] The buffer layer 3 has a thickness of 200 nm and a p-type doping concentration of 10 19 cm -3 Ga 0.3 Al 0.3 As buffer layer;

[0177] The emission layer 4 has a thickness of 800 nm and a p-type doping concentration of 10 19 cm -3 GaAs emission layer;

[0178] The activation layer 5 is a Cs:O activation layer with a thickness of 1 nm;

[0179] The preparation method of the transmission-type GaAs-based photocathode:

[0180] 1) Using MOCVD technology, GaAs with a thickness of 2 μm is deposited on the GaAs substrate. 0.5 Al 0.5 As corrosion barrier layer, GaAs emission layer 4 with a thickness of 800nm, Ga 0.3 Al 0.7 As buffer layer 3, Ga with a thickness of 350nm 0.3 Al 0.7 As grating prefabricated layer and GaAs protective layer with a thickness of 0.5 μm, and then remove the GaAs protective layer with a thickness of 0.5 μm by chemical etching to expose the GaAs with a thickness of 350 nm. 0.3 Al 0.7 As grating prefabricated layer;

[0181] 2) The Ga with a thickness of 350 nm 0.3 Al 0.7 The surface of the As grating prefabricated layer is etched into Ga 0.3 Al 0.7 After the As / air grating is prefabricated, the Ga 0.3 Al 0.7 As / air grating prefabricated structure surface is uniformly deposited with Si3N4 material (the Si3N4 material replaces the Ga 0.3 Al 0.7As / air grating prefabricated structure), the excess Si3N4 material on the surface is removed by mechanical polishing, and the Si3N4 surface is polished into an optical surface; at the same time, the Si3N4 material is removed from the Si3N4 / Ga 0.3 Al 0.7 As rectangular grating structure interface, on the side close to the SiO2 layer, the remaining Si3N4 material can also be regarded as a Si3N4 optical film with uniform thickness and thickness of 350 nanometers, that is, the Si3N4 optical film with a thickness of 350nm of the photocathode of the present invention, forming the grating layer 2 of the present invention: Si3N4 optical film (350nm) / Si3N4 / Ga 0.1 Al 0.9 As grating structure (350nm);

[0182] 3) depositing a SiO2 optical film with a thickness of about 100 nm on the surface of the Si3N4 optical film in the grating layer 2;

[0183] 4) After the light emitting side of the SiO2 layer 1 is closely attached to the SiO2 optical film, the grating layer 2 is bonded to the SiO2 layer 1 under vacuum heating conditions, and then the GaAs substrate, the GaAs layer with a thickness of 2 μm, and the GaAs layer with a thickness of 2 μm are removed in sequence by wet etching. 0.5 Al 0.5 As corrosion barrier layer and GaAs emission layer 4 with a thickness of 800nm;

[0184] 5) In vacuum degree ≤10 -7 Under ultra-high vacuum conditions of 1.5 Pa, a Cs:O activation layer 5 is deposited on the surface of the GaAs emission layer 4 with a thickness of 800 nm to form a negative electron affinity surface that is conducive to the emission of photoelectrons into the vacuum, thereby obtaining the transmission-type GaAs-based photocathode;

[0185] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A transmissive GaAs-based photocathode, characterized in that: The SiO2 layer, the grating layer, the buffer layer, the emission layer and the activation layer are sequentially stacked along the light incident direction; The grating layer comprises a Si3N4 optical film and a dielectric grating structure of a non-axisymmetric periodic unit; the dielectric grating structure is an incident grating interface and / or an exit grating interface.

2. The transmissive GaAs-based photocathode according to claim 1, characterized in that: The incident grating interface is a SiO2 / Si3N4 grating interface, and the exit grating interface is a Si3N4 / buffer layer grating structure.

3. The transmissive GaAs-based photocathode according to claim 1, characterized in that: The dielectric grating structure is a one-dimensional grating structure or a two-dimensional grating structure.

4. The transmissive GaAs-based photocathode according to claim 2 or 3, characterized in that: When the output grating interface is a Si3N4 / buffer layer grating structure, and the dielectric grating structure is a two-dimensional grating structure, the two-dimensional grating structure is a dielectric grating structure of a non-axisymmetric periodic unit, and the non-axisymmetric periodic unit refers to a long period and a short period in two periodic directions of the two-dimensional grating along the axis of the incident light. For each periodic unit, the long period / short period ≥ 2 / 1; the angle between the two periodic directions ≥ 45°.

5. The transmissive GaAs-based photocathode as claimed in claim 3, characterized in that: The grating period of the dielectric grating structure is 0.1 to 10 times of the response wavelength, the duty cycle is 0.2 to 0.8, and the grating height is 0.02 to 1 μm.

6. The transmissive GaAs-based photocathode according to any one of claims 2 to 3 or 5, characterized in that: Along the light incident direction, the grating layer includes a Si3N4 optical film and a Si3N4 / buffer layer exit grating interface arranged in sequence; Or the grating layer includes a SiO2 / Si3N4 incident grating interface and a Si3N4 optical film arranged in sequence; Or the grating layer includes a SiO2 / Si3N4 incident grating interface, a Si3N4 optical film and a Si3N4 / buffer layer exit grating interface which are arranged in sequence.

7. The transmissive GaAs-based photocathode according to claim 6, characterized in that: The thickness of the Si3N4 optical film is ≥30nm.

8. The transmissive GaAs-based photocathode according to claim 1, characterized in that: The thickness of the buffer layer is 10 nm to 2 μm, and the p-type doping concentration of the buffer layer is 10 18 ~10 19 cm -3 ; The doping concentration of the buffer layer remains unchanged, or decreases gradually from the body to the vacuum surface; The material of the buffer layer includes GaAlAs, InGaAlAs or GaAlAsP; When the material of the buffer layer is GaAlAs, the molar content of the Al component is 0.5-1, and the total molar amount of Ga and Al in the GaAlAs is 1; When the material of the buffer layer is InGaAlAs, the molar content of the Al component is 0.5-1, the molar content of In is 0-0.2, and the total molar amount of In, Ga and Al in the InGaAlAs is 1; When the material of the buffer layer is GaAlAsP, the molar content of the Al component is 0.5-1, the molar content of P is 0-0.5, the total molar amount of Ga and Al in the GaAlAsP is 1, and the total molar amount of As and P in the GaAlAsP is 1.

9. The transmissive GaAs-based photocathode according to claim 1, characterized in that: The thickness of the emission layer is 0.3 to 2.5 μm, and the p-type doping concentration of the emission layer is 10 18 ~10 19 cm -3 ; The doping concentration of the emission layer remains unchanged, or decreases gradually from the body to the vacuum surface; The bandgap width of the emission layer is always smaller than the bandgap width of the buffer layer; The material of the emission layer includes GaAs, InGaAs, AlGaAs or GaAsP, and the bandgap width of the emission layer remains unchanged or decreases gradually from the body to the vacuum surface; When the material of the emission layer includes InGaAs, the molar content of In is 0 to 0.2, and the total molar amount of In and Ga in the InGaAs is 1; When the material of the emission layer includes GaAlAs, the molar content of the Al component is 0 to 0.5, and the total molar amount of Ga and Al in the GaAlAs is 1; When the material of the emission layer includes GaAsP, the molar content of P is 0-0.5, and the total molar amount of As and P in the GaAsP is 1.

10. Use of the transmission photocathode according to any one of claims 1 to 9 in the field of low-light-level night vision, low-light-level remote sensing imaging or photomultiplier tubes.

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