阅读说明：本技术 近红外响应增强的叠层复合GaAs基光电阴极及其制备方法 (Laminated composite GaAs-based photocathode with enhanced near-infrared response and preparation method thereof ) 是由 张益军 王自衡 李姗 李诗曼 詹晶晶 张锴珉 钱芸生 于 2021-06-22 设计创作，主要内容包括：本发明公开了一种近红外响应增强的叠层复合GaAs基光电阴极及其制备方法。该光电阴极包括自下而上设置的衬底、GaAs缓冲层、In-(y)Al-(1-)-(y)As线性渐变缓冲层、p型In-(0.19)Al-(0.81)As腐蚀阻挡层、p型In-(x)Ga-(1-x)As变组分变掺杂发射层、DBR反射层和增透膜接触层,其中,DBR反射层由GaAs层与AlAs层按照特定周期交替生长组成。p型掺杂In-(x)Ga-(1-x)As发射层由不同In组分的多子层组成,各子层中In组分自内向外逐层由0.05递增到0.2。本发明一方面通过变组分生长技术,改善了原有InGaAs光电阴极的晶格匹配质量,提高了光电阴极的光电发射特性,增强了该光电阴极在全波段的响应。另一方面,通过引入DBR反射层,大幅提高了该光电阴极对近红外特定波长的光吸收能力,进一步提高了特定波长下的量子效率增强效果。(The invention discloses a laminated composite GaAs-based photocathode with enhanced near-infrared response and a preparation method thereof. The photoelectric cathode comprises a substrate, a GaAs buffer layer and In arranged from bottom to top y Al 1‑ y As linear graded buffer layer and p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type In x Ga 1‑x The light-emitting diode comprises an As component-variable and doping emission layer, a DBR reflection layer and an antireflection film contact layer, wherein the DBR reflection layer is formed by alternately growing GaAs layers and AlAs layers according to a specific period. p-type doped In x Ga 1‑x The As emission layer is composed of a plurality of sublayers with different In components, and the In components In each sublayer are gradually increased from 0.05 to 0.2 layer by layer from inside to outside. On one hand, the invention improves the lattice matching quality of the original InGaAs photocathode, improves the photoelectric emission characteristic of the photocathode and enhances the response of the photocathode in all wave bands by a variable-component growth technology. On the other handBy introducing the DBR reflecting layer, the light absorption capacity of the photoelectric cathode to near-infrared specific wavelength is greatly improved, and the quantum efficiency enhancement effect under the specific wavelength is further improved.)

1. The laminated composite GaAs-based photocathode with enhanced near-infrared response is characterized by comprising a substrate, a GaAs buffer layer and In arranged from bottom to top_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As corrosion barrier layer, p-type In_xGa_{1- x}An As emitting layer, a DBR reflecting layer and an antireflection film contact layer, the p-type In_xGa_1-xThe As emission layer adopts a variable-component variable-doping design, the In component linearly increases from top to bottom, and the doping concentration exponentially decreases from top to bottom.

2. The near-infrared response enhanced laminated composite GaAs-based photocathode according to claim 1, wherein the p-type In_xGa_1-xThe In component of the As emission layer is linearly increased from 0.05 to 0.2 from top to bottom, and the doping concentration is from 1 multiplied by 10 from top to bottom¹⁹cm^-3The index is decreased to 5.0 × 10¹⁸cm^-3The total thickness of the emitting layer is 1-1.3 μm.

3. The GaAs-based photocathode of claim 1, wherein the DBR reflective layer is formed by alternately growing two materials, a p-GaAs sublayer and a p-AlAs sublayer.

4. The GaAs-based photocathode of claim 3, wherein the p-type AlAs sublayer and the p-type GaAs sublayer have thicknesses that satisfy:

in the formula n_LAnd n_HRefractive indices of materials of AlAs and GaAs, respectively, d_LAnd d_HThe thicknesses of the AlAs sublayer and the GaAs sublayer, respectively, and λ is the specified total reflection center wavelength.

5. GaAs-based photocathode according to claim 3 or 4, wherein the p-type AlAs sub-layer has a thickness of 90nm, the p-type GaAs sub-layer has a thickness of 76nm, and the DBR reflective layer has a doping concentration of 1 x 10¹⁹cm^-3The DBR reflecting layer takes a pair of AlAs/GaAs sub-layers as a period, the period number of the alternating layers is not less than 3 pairs, the sub-layer close to the emitting layer (14) is a p-type GaAs sub-layer, and the sub-layer close to the antireflection film contact layer (10) is a p-type AlAs sub-layer.

6. The near-infrared response enhanced laminated composite GaAs-based photocathode according to claim 1, wherein the In_yAl_1-yThe In component of the As linear gradient buffer layer increases linearly from 0 to 0.22 from bottom to top, and the total thickness of the linear gradient buffer layer is 2-3 mu m.

7. The near-infrared response enhanced laminated composite GaAs-based photocathode according to claim 1, wherein the p-type In_0.19Al_0.81The In component of the As corrosion barrier layer is 0.19, the total thickness is 400-600 nm, and the doping concentration is 1 multiplied by 10¹⁸cm^-3。

8. The laminated composite GaAs-based photocathode of claim 1, wherein the antireflection film contact layer is a p-type GaAs material and has a doping concentration of 1 x 10¹⁹cm^-3The thickness is 300 to 500 nm.

9. The preparation method of the photocathode based on any one of claims 1 to 8, which is characterized by comprising the following specific steps:

step 1, growing a GaAs buffer layer and In on a substrate In sequence_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As corrosion barrier layer and p-type variable-composition variable-doping In_xGa_1-xThe light-emitting diode comprises an As emitting layer, a DBR reflecting layer and a p-type GaAs antireflection film contact layer;

step 2, cleaning the p-type GaAs antireflection film contact layer, depositing an antireflection film on the surface of the antireflection film contact layer, and thermally bonding the table top glass window on the antireflection film;

step 3, corroding the substrate, the GaAs buffer layer and In sequence through selective chemical reagents_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As etch stop layer, exposed emitter layer In_xGa_1-xAn As surface;

step 4, activating the p-type In through ultrahigh vacuum_xGa_1-xThe Cs/O activation is carried out on the surface of the As emitting layer, so that the surface of the emitting layerThe surface is covered with an activation layer to make the photocathode reach negative electron affinity.

10. The method for preparing a photocathode according to claim 9, wherein the ultra-high vacuum activation process in step 4 is specifically performed at a vacuum degree of not less than 10^-8And in the Pa ultrahigh vacuum environment, a Cs/O activation process is adopted, and the thickness of the Cs/O activation layer is 0.5-1.5 nm.

Technical Field

The invention belongs to the technical field of low-light-level night vision detection materials, and particularly relates to a laminated composite GaAs-based photocathode with enhanced near-infrared response and a preparation method thereof.

Background

The GaAs-based photocathode is developed based on a solid physical theory according to the guidance of a Spicer photoelectric emission three-step model theory. The GaAs-based photocathode has the advantages of high quantum efficiency, small dark current, large long-wave response expansion potential and the like, so the GaAs-based photocathode is widely applied in the field of modern low-light-level night vision technology and is an important component in a low-light-level image intensifier. In addition, the GaAs-based photocathode has the advantages of high emission current density, concentrated emission electron energy and angle distribution, high electron spin polarizability, small thermal emission and the like, and has important application in the fields of electron beam plane exposure, linear accelerators, high-energy physics and the like.

In the practical application of the GaAs-based photocathode, how to widen the spectral response range and improve the quantum efficiency of a near infrared band so as to improve the spectral matching between a night vision device and night light and improve the detection efficiency and the action distance of a low-light night vision detector under the night light becomes a hot problem concerned by researchers at home and abroad. In the near-infrared extension aspect of the GaAs-based photocathode, researchers improve the quantum efficiency of the photocathode in a 1.0-1.7 mu m wave band by adopting an InGaAs material for an emission layer, and realize the active detection and imaging of near-infrared laser. InGaAs photocathodes, as a direct bandgap photoemissive material, can theoretically extend the cutoff wavelength from 0.87 μm to 3.5 μm by changing the In composition. At present, through cathode structure improvement in the united states, the quantum efficiency of a prepared InGaAs photocathode reaches 1.2% at 1.06 μm, while the quantum efficiency of a transmission-type InGaAs photocathode prepared in China only reaches 0.005% at 1.06 μm, and the quantum efficiency of the transmission-type InGaAs photocathode reaches 0.76% at 1 μm, and the main reasons for the low quantum efficiency of the above InGaAs photocathode are that the lattice matching of cathode materials is poor and the surface barrier of a narrow forbidden band cathode is high, which greatly limits the emission efficiency of near infrared photoelectrons. In addition, the insufficient absorption rate of the InGaAs photocathode emitting layer to the incident light in the near infrared band also results in a low level of quantum efficiency in the near infrared band.

Disclosure of Invention

The invention aims to provide a laminated composite GaAs-based photocathode with enhanced near-infrared response and a preparation method thereof.

The technical scheme for realizing the purpose of the invention is as follows: a laminated composite GaAs-based photocathode with enhanced near-infrared response comprises a substrate, a GaAs buffer layer and In arranged from bottom to top_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As corrosion barrier layer, p-type In_xGa_1-xAn As emitting layer, a DBR reflecting layer and an antireflection film contact layer, the p-type In_xGa_1-xThe As emission layer adopts a variable-component variable-doping design, the In component linearly increases from top to bottom, and the doping concentration exponentially decreases from top to bottom.

Preferably, the p-type In_xGa_1-xThe In component of the As emission layer is linearly increased from 0.05 to 0.2 from top to bottom, and the doping concentration is from 1 multiplied by 10 from top to bottom¹⁹cm^-3The index is decreased to 5.0 × 10¹⁸cm^-3，The total thickness of the emitting layer is 1-1.3 μm.

Preferably, the DBR reflecting layer is formed by alternately growing two materials, namely a p-type GaAs sub-layer and a p-type AlAs sub-layer.

Preferably, the thicknesses of the p-type AlAs sublayer and the p-type GaAs sublayer satisfy:

in the formula n_LAnd n_HRefractive indices of materials of AlAs and GaAs, respectively, d_LAnd d_HThe thicknesses of the AlAs sublayer and the GaAs sublayer, respectively, and λ is the specified total reflection center wavelength.

Preferably, the thickness of the p-type AlAs sublayer is 90nm, the thickness of the p-type GaAs sublayer is 76nm, and the doping concentration of the DBR reflecting layer is 1 × 10¹⁹cm^-3The DBR reflecting layer takes a pair of AlAs/GaAs sub-layers as a period, the period number of the alternating layers is not less than 3 pairs, the sub-layer close to the emitting layer (14) is a p-type GaAs sub-layer, and the sub-layer close to the antireflection film contact layer (10) is a p-type AlAs sub-layer.

Preferably, the In_yAl_1-yThe In component of the As linear gradient buffer layer increases linearly from 0 to 0.22 from bottom to top, and the total thickness of the linear gradient buffer layer is 2-3 mu m.

Preferably, the p-type In_0.19Al_0.81The In component of the As corrosion barrier layer is 0.19, the total thickness is 400-600 nm, and the doping concentration is 1 multiplied by 10¹⁸cm^-3。

Preferably, the antireflection film contact layer is made of p-type GaAs material and has a doping concentration of 1 × 10¹⁹cm^-3The thickness is 300 to 500 nm.

The invention also provides a preparation method of the laminated composite GaAs-based photocathode with enhanced near-infrared response, which comprises the following specific steps:

step 1, growing a GaAs buffer layer and In on a substrate In sequence_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As corrosion barrier layer and p-type variable-composition variable-doping In_xGa_1-xThe light-emitting diode comprises an As emitting layer, a DBR reflecting layer and a p-type GaAs antireflection film contact layer;

step 2, cleaning the p-type GaAs antireflection film contact layer, depositing an antireflection film on the surface of the antireflection film contact layer, and thermally bonding the table top glass window on the antireflection film;

step 3, corroding the substrate, the GaAs buffer layer and In sequence through selective chemical reagents_yAl_1-yLinear gradual change of AsBuffer layer, p-type In_0.19Al_0.81As etch stop layer, exposed emitter layer In_xGa_1-xAn As surface;

step 4, activating the p-type In through ultrahigh vacuum_xGa_1-xAnd C/O activation is carried out on the surface of the As emitting layer, so that the surface of the emitting layer is covered with the activation layer, and the photocathode achieves negative electron affinity.

Compared with the prior art, the invention has the following remarkable advantages: 1) according to the invention, the DBR reflection layer is introduced, so that the absorption rate of the emission layer to incident light in a near-infrared band is improved, the spectral response and the quantum efficiency of the photoelectric cathode to the near-infrared band are improved, and the performance in practical application is improved; 2) the invention fully considers the lattice matching problem of each layer of material in the structural design of the photocathode, and ensures good lattice matching degree among sub-layers through variable components and reasonable material selection, thereby realizing higher quantum efficiency; 3) on the basis of the original reflection type photocathode, the back surface of the photocathode is coupled with the glass incidence window, so that the photocathode has the photoelectron emission capability when the back light is incident, and has more working modes compared with the traditional reflection type photocathode.

The present invention is described in further detail below with reference to the attached drawings.

Drawings

FIG. 1 is a schematic view of a photocathode growth structure.

Fig. 2 is a diagram of the band structure in the emissive layer of a photocathode.

FIG. 3 is a schematic diagram of the structure of the photocathode after corrosion and activation.

Fig. 4 is a graph of the reflectivity of a photocathode.

FIG. 5 shows a photocathode of the present invention with a DBR structure and In of a conventional DBR-free structure_xGa_1-xNormalized spectral response plot of As photocathode.

FIG. 6 is a graph of normalized spectral response and normalized incident spectrum for a photocathode in a back-illuminated incident operating mode.

Detailed Description

The invention is described in further detail below with reference to figures 1-6 and the detailed description.

As shown In FIG. 1, a laminated composite GaAs-based photocathode with enhanced near-infrared response comprises a substrate 22, a GaAs buffer layer 20, In_yAl_1-yAs linear graded buffer layer 18, p-type In_0.19Al_0.81As etch stop layer 16, p-type In_xGa_1-xAn As emitting layer 14, a DBR (distributed bragg reflector) reflecting layer 12, and an antireflection film contact layer 10. The p-type In_xGa_1-xThe As emitting layer 14 adopts a variable-composition variable-doping design, the In composition increases linearly from top to bottom, and the doping concentration decreases exponentially from top to bottom.

In a further embodiment, as shown In FIG. 2, the p-type In_xGa_1-xAs emitting layer In composition increases linearly from 0.05 to 0.2 from top to bottom, doping concentration is 1 × 10 from top to bottom¹⁹cm^-3The index is decreased to 5.0 × 10¹⁸cm^-3，The total thickness of the emitting layer is 1-1.3 μm. In the p-type emitting layer, due to the introduction of variable doping and variable composition design, the valence band (E) in the emitting layer_v) And conduction band (E)_c) The flat effect of the Fermi level generates the band bending phenomenon, and thus the built-in electric field (E) in the direction from outside to inside_in). Since the built-in electric field is opposite to the electron migration direction, excited electrons are drawn by the built-in electric field as they move towards the emission surface, resulting in more electrons moving to the emission surface and being emitted into the vacuum. Due to the DBR reflective layer, the incident light in the near infrared band is reflected by the DBR layer back to the emitting layer for secondary absorption after passing through the emitting layer. Therefore, the DBR layer increases the absorption capacity of the emitting layer to the incident light in the near-infrared band, and further improves the quantum efficiency of the photocathode.

In a further embodiment, the DBR reflecting layer is formed by alternately growing two materials, namely a p-type GaAs sub-layer and a p-type AlAs sub-layer.

In a further embodiment, the thicknesses of the p-type AlAs sublayer and the p-type GaAs sublayer satisfy:

in the formula n_LAnd n_HRefractive indices of materials of AlAs and GaAs, respectively, d_LAnd d_HThe thicknesses of the AlAs sublayer and the GaAs sublayer, respectively, and λ is the specified total reflection center wavelength.

In a further embodiment, the thickness of the p-type AlAs sublayer is 90nm, the thickness of the p-type GaAs sublayer is 76nm, and the doping concentration of the DBR reflective layer is 1 × 10¹⁹cm^-3The DBR reflecting layer takes a pair of AlAs/GaAs sub-layers as a period, the period number of the alternating layers is not less than 3 pairs, the sub-layer close to the emitting layer (14) is a p-type GaAs sub-layer, and the sub-layer close to the antireflection film contact layer (10) is a p-type AlAs sub-layer.

In a further embodiment, the In_yAl_1-yThe In component of the As linear gradient buffer layer increases linearly from 0 to 0.22 from bottom to top, and the total thickness of the linear gradient buffer layer is 2-3 mu m.

In further embodiments, the p-type In_0.19Al_0.81The In component of the As corrosion barrier layer is 0.19, the total thickness is 400-600 nm, and the doping concentration is 1 multiplied by 10¹⁸cm^-3。

In a further embodiment, the antireflection film contact layer is made of p-type GaAs material and has a doping concentration of 1 × 10¹⁹cm^-3The thickness is 300 to 500 nm.

Specifically, the substrate is a high substrate n-type GaAs (100) substrate.

The reflectance graph of the photocathode of the present invention is shown in fig. 4. As can be seen from the figure, due to the introduction of the DBR layer 12 at the rear end of the emitting layer, the reflectance has large amplitude oscillation fluctuation in the near infrared spectrum, because the reflectance spectrum of the DBR layer 12 itself has the oscillation characteristic in the near infrared. Since the DBR structure can only realize the total reflection effect at a specific wavelength, the present embodiment only enhances the absorption rate at 1064 nm. According to a formula designed by a DBR, when the total reflection of a specific wavelength is realized, the thicknesses of two sublayers need to satisfy the following relational expression:

in the formula n_LAnd n_HRefractive indices of materials of AlAs and GaAs, respectively, d_LAnd d_HThe thicknesses of the AlAs sublayer and the GaAs sublayer, respectively, and λ is the specified total reflection center wavelength. As can be seen from fig. 4, the reflectivity of the present invention reaches a minimum at 1064nm, indicating that the absorption at 1064nm is significantly improved compared to the conventional structure.

FIG. 5 shows a conventional In without DBR reflective layer_xGa_1-xGraph comparing the normalized spectral response of an As photocathode with the novel structure proposed by the present invention. It can be seen that for the spectral response of a conventional structure photocathode, the spectral response curve smoothly decreases as the wavelength increases in the near infrared band due to the absence of the DBR reflective layer. The reflectivity of the near-infrared band vibrates due to the introduced DBR reflecting layer, and two maximum value peaks appear in the quantum efficiency at 990nm and 1064 nm. This is because the DBR layer structure is at the maximum of the reflectivity curve at these two wavelengths, resulting in enhanced absorption by the photocathode at these two wavelengths, thereby increasing the quantum efficiency at these two wavelengths. Since the InGaAs emitting layer originally has a good absorption capability for visible light, the secondary absorption effect caused by the DBR reflective layer in the visible light band is small, and it can be seen that the spectral response is not greatly affected by the presence or absence of the DBR reflective layer in the visible light band.

FIG. 6 is a graph of normalized spectral response and normalized incidence for a photocathode of the present invention under back-illuminated incidenceAnd the spectrum graph shows a back-illuminated working mode when the incident light is incident to the photoelectric cathode from the surface of the glass. At this time, due to the antireflection film contact layer 10 and the DBR layer 12, incident light In the visible light band is absorbed In a large amount, resulting In_xGa_1-xThe incident spectrum of the As emitting layer 14 is dominated by the near infrared band, As shown by the dotted line in fig. 6. At this time, the incident light below 650nm is completely absorbed by the antireflection film contact layer 10 and the DBR reflection layer 12, and the near-infrared incident light undergoes significant oscillation due to the presence of the DBR reflection layer 12, so that the incident spectrum assumes a non-uniform state. The maximum of the spectral response is still reached at 1064 nm. The photocathode of the invention has low spectral response to visible light in the working mode, but still has high spectral response in the near infrared band.

In addition, the back of the photocathode is bonded with glass, so that the photocathode has two working modes of a normal incidence mode and a back illumination mode, and the using scene is expanded.

As shown in fig. 3, a method for preparing a laminated composite GaAs-based photocathode with enhanced near-infrared response specifically comprises the steps of:

step 1, growing a GaAs buffer layer and In on a substrate In sequence_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As corrosion barrier layer and p-type variable-composition variable-doping In_xGa_1-xThe light-emitting diode comprises an As emitting layer, a DBR reflecting layer and a p-type GaAs antireflection film contact layer;

step 2, cleaning the p-type GaAs antireflection film contact layer, depositing an antireflection film on the surface of the antireflection film contact layer, and thermally bonding the table top glass window on the antireflection film;

step 3, corroding the substrate, the GaAs buffer layer and In sequence through selective chemical reagents_yAl_1-yAs linear graded buffer layer and p-type In_0.19Al_0.81As etch stop layer, exposed emitter layer In_xGa_1-xAn As surface;

step 4, activating the p-type In through ultrahigh vacuum_xGa_1-xThe surface of the As emission layer is activated by Cs/O to cover the surface of the emission layerAnd covering the active layer to make the photocathode reach negative electron affinity.

As can be seen from the figure, the original substrate 22, GaAs buffer layer 20 and In are required to be firstly arranged In the preparation process_yAl_1-yThe As linear graded buffer layer 18 is selectively etched in sequence by using corresponding etching reagents, so that the surface of the emitting layer 14 is exposed. And then plating an antireflection film 26 on one side of the antireflection film contact layer 10, and adhering glass 28 to the device by a thermal adhesion technology to protect the photocathode. Finally, in the ultra-high vacuum cavity, a Cs/O active layer 24 is grown on the surface of the emitting layer 14 by the surface activation technology of the photocathode, so that the electron emission capability of the photocathode is improved, and the photocathode achieves negative electron affinity.

The invention improves the quantum efficiency and spectral response of the GaAs-based photocathode in the near-infrared band. Because the emitting layer in the laminated composite GaAs-based photocathode with enhanced near-infrared response adopts the variable-component variable-doping design, under the action of a Fermi level, the energy band of the photocathode bends and generates a built-in electric field. The design is favorable for improving the spectral response of the photocathode in a full response wave band because a built-in electric field generated by band bending has the characteristic of pulling electrons to move to an emission surface, and the number of electrons reaching the emission surface of the photocathode is increased. In addition, the DBR reflecting layer is introduced between the emitting layer and the antireflection film contact layer as an intermediate layer. Due to its special optical properties, a DBR reflective layer consisting of two lattice matched materials grown alternately can achieve total reflection of incident light of a specific wavelength. Compared with the traditional GaAs-based photocathode, most incident light passes through the emitting layer and the substrate and is dissipated in use due to the lower absorption capacity of the emitting layer for the near infrared band. But increasing the thickness does not have a significant effect on the absorption yield improvement and the lattice mismatch as the material is grown is proportional to the emitter layer thickness. Therefore, the DBR reflecting layer is introduced, so that the incident light which is originally transmitted by the substrate under a certain specific wavelength is reflected back to the emitting layer for secondary absorption on the premise of not increasing the thickness of the emitting layer, the absorption rate of the emitting layer to the specific wavelength is improved, and the spectral response of the GaAs-based photoelectric cathode to the wavelength is finally improved.

The invention has higher quantum efficiency for near-infrared incident light than the traditional structure, and simultaneously has two working modes of a front incidence mode and a back illumination mode.

Example 1

A laminated composite GaAs-based photocathode with enhanced near-infrared response sequentially grows a GaAs buffer layer 20 and In on a high-quality n-type GaAs substrate 22 by MOCVD_yAl_1-yAs linearly graded buffer layer 18, p-type In_0.19Al_0.81As etch stop layer 16, p-type In_xGa_1-xAn As emitting layer 14, a DBR reflecting layer 12 and an antireflection film contact layer 10, wherein all the doping atoms of the epitaxial layers are Zn-doped.

The GaAs buffer layer 20 is intrinsic GaAs material, and is directly epitaxially grown on GaAs substrate 22 with a thickness of 100nm as substrate and In_yAl_1-yThe buffer material of the As linearly graded buffer layer 18.

In_yAl_1-yAn As linearly graded buffer layer 18 is grown over the GaAs buffer layer 20, with a total thickness of 2500nm and without doping. The buffer layer is grown with a linearly graded composition, and the In composition increases linearly from 0 to 0.22 from bottom to top.

p-type In_0.19Al_0.81As etch stop layer 16 grown In_yAl_1-yOn the As linear graded buffer layer 18, the doping concentration is 1 × 10¹⁸cm^-3The thickness was 500nm, and the In composition was constant at 0.19.

p-type In_xGa_1-xAs emitter layer 14 is grown In p-type In_0.19Al_0.81Above the As etch stop layer 16, the emitter layer may be divided into 4 sublayers with different In compositions and different doping concentrations, and the thickness of each sublayer is different. The In components of the sub-layers are respectively 0.2, 0.15, 0.1 and 0.05 from bottom to top, and the doping concentrations are respectively 5 multiplied by 10 from bottom to top¹⁸cm^-3，6.5×10¹⁸cm^-3，8.5×10¹⁸cm^-3，1×10¹⁹cm^-3The thicknesses of the sublayers are 0.3 μm from bottom to top, and the total thickness of the emission layer is 1.2 μm. Due to InGaAs material pairThe absorption capacity of incident light In the near infrared band is positively correlated with the In composition, and therefore, In the emission layer, a sub-layer having an In composition of 0.2 occupies a major portion. By means of the mode of variable-component growth, the lattice matching degree of materials between the emitting layer and the adjacent layer during growth can be improved, and a sample with better quality is obtained.

The DBR reflective layer 12 is formed by alternately growing p-type GaAs sub-layers and p-type AlAs sub-layers, and is grown on the emission layer 10 layer by layer. Wherein each GaAs sublayer has a thickness of 76nm and a doping concentration of 1 × 10¹⁹cm^-3Each AlAs sublayer has a thickness of 90nm and a doping concentration of 1X 10¹⁹cm^-3. The sublayer adjacent to the emitting layer is a GaAs sublayer, and the sublayer on the farthest side of the emitting layer is an AlAs sublayer. The number of alternating periods of the DBR layers was 10, for a total of 10 GaAs sublayers and 10 AlAs sublayers, and the total thickness of the DBR layers was 1660 nm.

An antireflection film contact layer 10 is grown on the DBR layer 12, on the AlAs sub-layer surface. The contact layer 10 of the antireflection film has a doping concentration of 1 × 10¹⁹cm^-3Has a thickness of 400 nm. Antireflection film contact layer 10 is mainly used to protect the DBR layer and the photocathode during antireflection film growth and thermal bonding.

A preparation method of a laminated composite GaAs-based photocathode with enhanced near-infrared response comprises the following steps:

growing an undoped GaAs buffer layer 20 with a thickness of 100nm by MOCVD on a (100) crystal face of a high-quality n-type GaAs substrate 22, and then growing In with an In composition linearly increased from 0 to 0.22 and a thickness of 2500nm on the GaAs buffer layer 20_yAl_1-yAs linear graded buffer layer 18 and a thickness of 500nm and a doping concentration of 1 × 10¹⁸cm^-3P-type In of_0.19Al_0.81As corrodes the barrier layer 16. Then according to figure 6, the silicon nitride is grown in the thickness of 1.2 μm and the doping concentration is from 5X 10 from bottom to top¹⁸cm^-3Exponential increase of 1 × 10¹⁹cm^-3P-type In with In component decreasing from 0.2 to 0.05 from bottom to top_xGa_1-xAn As emitting layer 14, a DBR reflecting layer 12 composed of p-type AlAs sub-layers and p-type GaAs sub-layers alternately grown, with a thickness of 400nm and a doping concentration of 1 × 10¹⁹cm^-3P-type GaAs anti-reflection film contact layer 10. Wherein the thickness of AlAs sublayer in DBR reflecting layer 12 is 90nm, the thickness of GaAs sublayer is 76nm, and the doping concentration of all sublayers is 1 × 10¹⁹cm^-3. In addition, In the DBR reflective layer 12_xGa_1-xThe As emission layer is closely attached to a GaAs sublayer, the AlAs sublayer is closely attached to the permeation enhancing film contact layer 10, and the alternating period number is 10 times. All the above doping uses Zn atom doping.

And cleaning the surface of the antireflection film contact layer 10 by using ultrasonic waves and a chemical solution to make the surface of the antireflection film contact layer hit an atomic-level cleaning surface. An antireflective film 26 with a thickness of 100nm is then deposited on the surface of antireflective film contact layer 10 by Plasma Enhanced Chemical Vapor Deposition (PECVD), followed by thermal bonding of a mesa glass window 28 over antireflective film 26.

Etching the high-quality n-type GaAs (100) substrate 22, the GaAs buffer layer 20 and In sequence by corresponding selective chemical etching method_yAl_1-yAs linearly graded buffer layer 18 and p-type In_0.19Al_0.81As etching the barrier layer 16 to make In_xGa_1-xThe As emission layer 14 is surface exposed.

At vacuum degree of not less than 10^-8In the Pa ultrahigh vacuum test system, a Cs source continuous and O source discontinuous photocathode surface activation process is adopted to lead In_xGa_1-xA Cs/O active layer 24 with the thickness of about 1.5nm is formed on the surface of the As emitting layer 14, and the surface of the emitting layer of the photocathode realizes a negative electron affinity state.