CN113690119B - Near-infrared response enhanced laminated composite GaAs-based photocathode and preparation method thereof - Google Patents
Near-infrared response enhanced laminated composite GaAs-based photocathode and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a laminated composite GaAs-based photocathode with enhanced near infrared response and a preparation method thereof. The photocathode comprises a substrate, a GaAs buffer layer and In arranged from bottom to top y Al 1‑ y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type In x Ga 1‑x The semiconductor device comprises an As variable component variable doped emission layer, a DBR reflection layer and an antireflection film contact layer, wherein the DBR reflection layer is formed by alternately growing a GaAs layer and an AlAs layer according to a specific period. P-doped In x Ga 1‑x The As emission layer is composed of multiple sublayers of different In compositions, with the In composition In each sublayer increasing from 0.05 to 0.2 from inside to outside. On one hand, the invention improves the lattice matching quality of the original InGaAs photocathode by a variable component growth technology, improves the photoelectric emission characteristic of the photocathode, and enhances the response of the photocathode in the whole wave band. On the other hand, by 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 specific wavelength is further improved.
Description
Technical Field
The invention belongs to the technical field of low-light 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 solid physical theory according to the three-step model theory of Spicer photoelectric emission. The GaAs-based photocathode has the advantages of high quantum efficiency, small dark current, large long-wave response expansion potential and the like, so that the GaAs-based photocathode is widely applied to the technical field of modern low-light night vision and is an important component in a low-light image intensifier. Besides, the GaAs-based photocathode has the advantages of high emission current density, concentrated emission electron energy and angle distribution, high electron spin polarization rate, small thermal emission and the like, and has important application in the fields of electron beam plane exposure, linear accelerator, 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 the near infrared band, thereby improving the spectral matching of a night vision device and night light, improving the detection efficiency and the action distance of a low-light night vision detector under the night light, and becoming a hot spot problem focused by researchers at home and abroad. In the near infrared extension aspect of the GaAs-based photocathode, researchers adopt InGaAs materials to improve the quantum efficiency of the photocathode in the wave band of 1.0-1.7 mu m for the emission layer, so as to realize the active detection and imaging of near infrared laser. InGaAs photocathodes as a direct bandgap photoemission material can theoretically be extended from 0.87 μm to 3.5 μm by varying the In composition cutoff wavelength. At present, the quantum efficiency of the prepared InGaAs photocathode reaches 1.2% at the position of 1.06 mu m through cathode structure improvement in the United states, the quantum efficiency of the prepared transmissive InGaAs photocathode at the position of 1.06 mu m only reaches 0.005%, and the quantum efficiency of the transmissive InGaAs photocathode at the position of 1 mu m reaches 0.76%, so that the main reasons of the low quantum efficiency of the above InGaAs photocathode are that the lattice matching difference of cathode materials and the high potential barrier of the cathode surface with a narrow forbidden band greatly limit the emission efficiency of near infrared photoelectrons. In addition, the lack of absorptivity of the InGaAs photocathode emission layer to near infrared incident light also results in a low level of quantum efficiency in the near infrared.
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: laminate with enhanced near infrared responseThe composite GaAs-based photocathode comprises a substrate, a GaAs buffer layer and In which are arranged from bottom to top y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type In x Ga 1-x An As emission layer, a DBR reflection layer and an antireflection film contact layer, the p-type In x Ga 1-x The As emission layer adopts a variable component and variable doping design, the In component is linearly increased from top to bottom, and the doping concentration is exponentially decreased from top to bottom.
Preferably, the p-type In x Ga 1-x The In component of the As emitting layer increases from 0.05 to 0.2 linearly from top to bottom, and the doping concentration is 1×10 from top to bottom 19 cm -3 Decreasing the index to 5.0X10 18 cm -3 The total thickness of the emitting layer is 1 μm to 1.3 μm.
Preferably, the DBR reflective layer is formed by alternately growing two materials, a p-type GaAs sub-layer and a p-type AlAs sub-layer.
Preferably, the thicknesses of the p-type AlAs sub-layer and the p-type GaAs sub-layer satisfy:
in n L And n H Refractive index of material of AlAs and GaAs, respectively, d L And d H The thicknesses of the AlAs and GaAs sublayers, respectively, lambda is the designated total reflection center wavelength.
Preferably, 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 reflection layers each have a doping concentration of 1×10 19 cm -3 The DBR reflection layer takes a pair of AlAs/GaAs sublayers as a period, the period number of the alternate layers is not less than 3 pairs, the sublayer close to the emission layer (14) is a p-type GaAs sublayer, and the sublayer close to the antireflection film contact layer (10) is a p-type AlAs sublayer.
Preferably, the In y Al 1-y As linear gradual change buffer layerThe In component increases from 0 to 0.22 In a linear way, and the total thickness of the linear gradual change buffer layer is 2-3 mu m.
Preferably, the p-type In 0.19 Al 0.81 The 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 10 18 cm -3 。
Preferably, the contact layer of the antireflection film is made of p-type GaAs material with doping concentration of 1 multiplied by 10 19 cm -3 The thickness is 300-500 nm.
The invention also provides a preparation method of the near infrared response enhanced laminated composite GaAs-based photocathode, which comprises the following specific steps:
step 1, growing a GaAs buffer layer and In on a substrate In sequence y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type variable component variable doped In x Ga 1-x An As emission layer, a DBR reflection layer and a p-type GaAs antireflection film contact layer;
step 2, cleaning a p-type GaAs antireflection film contact layer, depositing an antireflection film on the surface of the antireflection film contact layer, and thermally bonding a table glass window on the antireflection film;
step 3, sequentially corroding the substrate, the GaAs buffer layer and the In by using selective chemical reagents y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, bare emitter layer In x Ga 1-x An As surface;
step 4, performing ultra-high vacuum activation process on the p-type In x Ga 1-x Cs/O activation is carried out on the surface of the As emitting layer, so that the surface of the emitting layer covers the activating layer, and the photocathode reaches negative electron affinity.
Compared with the prior art, the invention has the remarkable advantages that: 1) According to the invention, the DBR reflection layer is introduced, so that the absorption rate of the emission layer to the incident light of the 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) According to the invention, the lattice matching problem of each layer of material is fully considered in the structural design of the photocathode, and good lattice matching degree among all sub-layers is ensured through component change and reasonable material selection, so that higher quantum efficiency is realized; 3) On the basis of the original reflective photocathode, the glass incident window is coupled to the back surface of the photocathode, so that the photocathode has the same photoelectron emission capability when the backlight is incident, and has more working modes compared with the traditional reflective photocathode.
The present invention will be described in further detail with reference to the accompanying drawings.
Drawings
Fig. 1 is a schematic view of a photocathode growth structure.
Fig. 2 is a diagram of the energy band structure in the photocathode emission layer.
FIG. 3 is a schematic view of the structure after photocathode etching and activation.
Fig. 4 is a graph of reflectivity of a photocathode.
FIG. 5 shows a photo-cathode of the present invention with DBR structure and an In with conventional DBR-free structure x Ga 1-x Normalized spectral response curve for an As photocathode.
Fig. 6 is a graph of normalized spectral response and normalized incident spectrum of a photocathode in a back-illuminated incident mode of operation.
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 near infrared response enhanced laminated composite GaAs-based photocathode comprises a substrate 22, a GaAs buffer layer 20, in arranged from bottom to top y Al 1-y As linear graded buffer layer 18, p-type In 0.19 Al 0.81 As etch stop layer 16, p-type In x Ga 1-x An As emission layer 14, a DBR (distributed bragg reflector) reflection layer 12 and an antireflection film contact layer 10. The p-type In x Ga 1-x The As emitter 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 x Ga 1-x As emission layer In groupThe doping concentration is 1 multiplied by 10 from top to bottom, wherein the doping concentration is linearly increased from 0.05 to 0.2 from top to bottom 19 cm -3 Decreasing the index to 5.0X10 18 cm -3 The total thickness of the emitting layer is 1 μm to 1.3 μm. In the p-type emissive layer, due to the introduction of the metamorphic doping and metamaterials design, the valence band (E v ) And conduction band (E) c ) Because of the fermi level leveling effect, the band bending phenomenon occurs, and thus a built-in electric field (E in ). Since the built-in electric field is opposite to the electron transfer direction, the excited electrons are pulled 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 to the vacuum. Due to the presence of the DBR reflective layer, incident light in the near infrared band is reflected back to the reflective layer by the DBR layer for secondary absorption after passing through the reflective layer. Therefore, the DBR layer increases the absorption capacity of the emission layer to the incident light of the near infrared band, and further improves the quantum efficiency of the photocathode.
In a further embodiment, the DBR reflective layer is formed by alternately growing two materials, a p-type GaAs sub-layer and a p-type AlAs sub-layer.
In a further embodiment, the thicknesses of the p-type AlAs sub-layer and the p-type GaAs sub-layer satisfy:
in n L And n H Refractive index of material of AlAs and GaAs, respectively, d L And d H The thicknesses of the AlAs and GaAs sublayers, respectively, lambda is the designated total reflection center wavelength.
In a further embodiment, 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 reflection layers have a doping concentration of 1×10 19 cm -3 The DBR reflection layer takes a pair of AlAs/GaAs sublayers as a period, the period number of the alternate layers is not less than 3 pairs, andthe sub-layer close to the emission 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 y Al 1-y The In component of the As linear gradual change buffer layer increases from 0 to 0.22 from bottom to top, and the total thickness of the linear gradual change buffer layer is 2-3 mu m.
In a further embodiment, the p-type In 0.19 Al 0.81 The 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 10 18 cm -3 。
In a further embodiment, the contact layer of the antireflection film is made of p-type GaAs material and has a doping concentration of 1×10 19 cm -3 The thickness is 300-500 nm.
Specifically, the substrate is a high substrate n-type GaAs (100) substrate.
The reflectance profile 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 emission layer, a large amplitude of oscillation fluctuation occurs in the near infrared spectrum of the reflectivity because the reflectivity spectrum of the DBR layer 12 itself has the characteristic of oscillation in the near infrared. Since the DBR structure can only achieve the total reflection effect at a specific wavelength, this embodiment enhances the absorption at 1064nm only. According to the formula of DBR design, when realizing total reflection at a specific wavelength, the thicknesses of the two sub-layers need to satisfy the following relation:
in n L And n H Refractive index of material of AlAs and GaAs, respectively, d L And d H The thicknesses of the AlAs and GaAs sublayers, respectively, lambda is the designated total reflection center wavelength. As can be seen from FIG. 4, the reflectivity of the present invention reaches a minimum at 1064nm, which isThe absorption at 1064nm is obviously improved compared with the traditional structure.
FIG. 5 shows a conventional In without DBR reflection layer x Ga 1-x Comparison of normalized spectral response of As photocathodes with the novel structure proposed by the present invention. It can be seen that the spectral response of the photocathode of the conventional structure is smoothly reduced in the near infrared band as the wavelength increases due to the absence of the DBR reflective layer. According to the invention, due to the introduced DBR reflecting layer, the reflectivity of the near infrared band is oscillated, and two maximum peaks appear at 990nm and 1064nm of quantum efficiency. This is because the DBR layer structure is located at the maximum of the reflectivity curve at these two wavelengths, resulting in enhanced photocathode absorptivity at these two wavelengths, thereby improving quantum efficiency at these two wavelengths. Since the InGaAs emission layer originally has a good absorption capacity for visible light, the influence of secondary absorption by the DBR reflection layer in the visible light band is small, and it can be seen that the presence or absence of the DBR reflection layer in the visible light band has little influence on the spectral response.
FIG. 6 is a graph of normalized spectral response and normalized incidence spectrum for a photocathode of the present invention in the case of back-illuminated incidence, in back-illuminated mode of operation when incident light is incident to the photocathode from a glass surface. At this time, incident light In the visible light band is largely absorbed due to the presence of the antireflection film contact layer 10 and the DBR layer 12, resulting In entry of In x Ga 1-x The incident spectrum of the As-emitting layer 14 is dominated by the near infrared band, as shown by the dashed line in fig. 6. At this time, the incident light below 650nm has been completely absorbed by the anti-reflection film contact layer 10 and the DBR reflection layer 12, and the near infrared incident light has a significant oscillation due to the DBR reflection layer 12, so that the incident spectrum exhibits an uneven state. At this point the maximum of the spectral response is still reached at 1064 nm. In this mode of operation, the photocathode of the present invention has a lower spectral response to visible light, but still has a higher spectral response in the near infrared band.
In addition, the glass is adhered to the back of the photocathode, so that the photocathode has two working modes of normal incidence and back illumination, and the use scene is expanded.
As shown in FIG. 3, the preparation method of the laminated composite GaAs-based photocathode with enhanced near infrared response comprises the following specific steps:
step 1, growing a GaAs buffer layer and In on a substrate In sequence y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type variable component variable doped In x Ga 1-x An As emission layer, a DBR reflection layer and a p-type GaAs antireflection film contact layer;
step 2, cleaning a p-type GaAs antireflection film contact layer, depositing an antireflection film on the surface of the antireflection film contact layer, and thermally bonding a table glass window on the antireflection film;
step 3, sequentially corroding the substrate, the GaAs buffer layer and the In by using selective chemical reagents y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, bare emitter layer In x Ga 1-x An As surface;
step 4, performing ultra-high vacuum activation process on the p-type In x Ga 1-x Cs/O activation is carried out on the surface of the As emitting layer, so that the surface of the emitting layer covers the activating layer, and the photocathode reaches negative electron affinity.
As can be seen from the figure, the original substrate 22, gaAs buffer layer 20, in are first required to be processed y Al 1-y The As linearly graded buffer layer 18 is sequentially selectively etched with a corresponding etchant to expose the surface of the emissive layer 14. After the anti-reflection film 26 is plated on one side of the anti-reflection film contact layer 10, the glass 28 is adhered to the device through a thermal adhesion technology, so that the function of protecting the photoelectric cathode is achieved. Finally, in the ultra-high vacuum chamber, the Cs/O activation layer 24 is grown on the surface of the emission layer 14 by the surface activation technology of the photocathode to improve the electron emission capability of the photocathode, so that the photocathode reaches negative electron affinity.
The invention improves the quantum efficiency and the spectral response of the GaAs-based photocathode in the near infrared band. Because the emitting layer in the near infrared response enhanced laminated composite GaAs-based photocathode adopts a variable component variable doping design, the energy band of the photocathode is bent and a built-in electric field is generated under the action of the Fermi energy level. The built-in electric field generated by the band bending has the characteristic of pulling electrons to move to the emission surface, and the number of electrons reaching the emission surface of the photocathode is increased, so that the design is beneficial to improving the spectral response of the photocathode in a full response band. In addition, the invention introduces a DBR reflecting layer as an intermediate layer between the emitting layer and the anti-reflection film contact layer. Due to its special optical properties, the DBR reflective layer, which is composed of two lattice matched materials grown alternately, can achieve total reflection of incident light at a specific wavelength. Compared to conventional GaAs-based photocathodes, most of the incident light will pass through the emissive layer and the substrate and dissipate in use due to the lower absorption capacity of the emissive layer for the near infrared band. However, increasing the thickness has no significant effect on the absorption enhancement and the lattice mismatch as the material grows is proportional to the emissive layer thickness. Therefore, the introduction of the DBR reflecting layer can lead the incident light which is originally transmitted by the substrate under a certain specific wavelength to be reflected back to the emitting layer for secondary absorption on the premise of not increasing the thickness of the emitting layer, thereby improving the absorption rate of the emitting layer to the specific wavelength and finally improving the spectral response of the GaAs-based photoelectric cathode to the wavelength.
The invention has higher quantum efficiency than the traditional structure for near infrared incident light, and has two working modes of normal incidence and back illumination.
Example 1
A near infrared response enhanced laminated composite GaAs-based photocathode is provided, on a high quality n-type GaAs substrate 22, MOCVD sequentially grows a GaAs buffer layer 20, in sequence y Al 1-y As linear graded buffer layer 18, p-type In 0.19 Al 0.81 As etch stop layer 16, p-type In x Ga 1-x An As emitter layer 14, a DBR reflector layer 12, and an anti-reflection film contact layer 10, wherein all epitaxial layers are Zn-doped with doping atoms.
The GaAs buffer layer 20 is an intrinsic GaAs material and is directly epitaxially grown on the GaAs substrate 22 to a thickness of 100nm as a substrate and In y Al 1-y As linearly graded buffer layer 18.
In y Al 1-y An As linear graded buffer layer 18 is grown over GaAs buffer layer 20 to a total thickness of 2500nm and is undoped. The buffer layer is grown with a linearly graded composition, with the In composition increasing linearly from 0 to 0.22 from bottom to top.
p-type In 0.19 Al 0.81 As etch stop layer 16 is grown In y Al 1-y On the As linear graded buffer layer 18, the doping concentration is 1×10 18 cm -3 The thickness was 500nm, and the in component was a constant value of 0.19.
p-type In x Ga 1-x As emitter layer 14 is grown on p-type In 0.19 Al 0.81 Above the As etch stop layer 16, the emissive layer may be divided into 4 sub-layers of different In composition and doping concentration, each sub-layer having a different thickness. The In component of each sublayer is 0.2,0.15,0.1,0.05 from bottom to top, and the doping concentration is 5×10 from bottom to top 18 cm -3 ，6.5×10 18 cm -3 ，8.5×10 18 cm -3 ，1×10 19 cm -3 The thicknesses of all the sub-layers are 0.3 μm from bottom to top, and the total thickness of the emission layer is 1.2 μm. Since the absorption capacity of InGaAs material for near infrared band incident light is positively correlated with the In composition, a sub-layer of 0.2 In composition occupies a major part In the emission layer. By means of the growth of the variable components, the lattice matching degree of the materials between the emitting layer and the adjacent layers can be improved during the growth of the materials, and samples with better quality can be obtained.
The DBR reflective layer 12 is formed by alternately growing p-type GaAs sublayers and p-type AlAs sublayers and grown layer by layer over the emissive layer 10. Wherein each GaAs sub-layer has a thickness of 76nm and a doping concentration of 1×10 19 cm -3 Each AlAs sub-layer has a thickness of 90nm and a doping concentration of 1×10 19 cm -3 . The sub-layer adjacent to the emission layer is a GaAs sub-layer, and the sub-layer on the furthest side of the emission layer is an AlAs sub-layer. The number of alternation cycles of the DBR layer was 10, and there were 10 GaAs sublayers and 10 AlAs sublayers in total, and the total thickness of the DBR layer was 1660nm.
The anti-reflection film contact layer 10 is grown on the DBR layer 12 and on the AlAs sub-layer surface. The doping concentration of the anti-reflection film contact layer 10 is 1 multiplied by 10 19 cm -3 P-type GaAs composition of 400nm in thickness. The anti-reflection film contact layer 10 is mainly used for protecting the DBR layer and the photocathode during the growth and thermal adhesion of the anti-reflection film.
The preparation method of the near infrared response enhanced laminated composite GaAs-based photocathode comprises the following steps:
on the (100) crystal face of the high-quality n-type GaAs substrate 22, an undoped GaAs buffer layer 20 having a thickness of 100nm is grown by MOCVD, and then an In having an In composition linearly increasing from 0 to 0.22 having a thickness of 2500nm is grown on the GaAs buffer layer 20 y Al 1-y As linear graded buffer layer 18 with a thickness of 500nm and a doping concentration of 1X 10 18 cm -3 P-type In of (2) 0.19 Al 0.81 As etch stop layer 16. Then according to FIG. 6, a layer of 1.2 μm thick and a doping concentration of 5X 10 from bottom to top were grown in sequence 18 cm -3 The index increment is 1×10 19 cm -3 The In composition is decreased from 0.2 to 0.05 from bottom to top x Ga 1-x An As emission layer 14, a DBR reflection layer 12 composed of alternately grown p-type AlAs sub-layers and p-type GaAs sub-layers, having a thickness of 400nm and a doping concentration of 1×10 19 cm -3 P-type GaAs antireflection film contact layer 10 of (c). Wherein the AlAs sub-layer thickness in the DBR reflection layer 12 is 90nm, the GaAs sub-layer thickness is 76nm, and the doping concentration of all sub-layers is 1×10 19 cm -3 . In and In the DBR reflection layer 12 x Ga 1-x The As emitting layer is tightly attached to the GaAs sub-layer, the AlAs sub-layer is tightly attached to the anti-reflection film contact layer 10, and the alternating cycle number is 10 times. All of the above doping uses Zn atom doping.
The surface of the anti-reflection film contact layer 10 is cleaned by ultrasonic waves and chemical solution so as to be driven to an atomically clean surface. An anti-reflection film 26 having a thickness of 100nm is then deposited on the surface of the anti-reflection film contact layer 10 by a Plasma Enhanced Chemical Vapor Deposition (PECVD), and then a mesa glass window 28 is bonded on top of the anti-reflection film 26 by a thermal bonding technique.
High quality n-type GaAs (100) substrate 22, gaAs buffer layer 20, in are etched sequentially using a corresponding selective chemical etching process y Al 1-y As linear graded buffer layer 18 and p-type In 0.19 Al 0.81 As etches the barrier layer 16 causing In x Ga 1-x The As emitter layer 14 surface is exposed.
At a vacuum degree of not less than 10 -8 In the Pa ultrahigh vacuum test system, a photocathode surface activation process with continuous Cs source and intermittent O source is adopted to enable In to be x Ga 1-x The Cs/O activation layer 24 with a thickness of about 1.5nm is formed on the surface of the As emission layer 14, and at this time, the negative electron affinity state is realized on the emission layer surface of the photocathode.
Claims (6)
1. A near infrared response enhanced laminated composite GaAs-based photocathode is characterized by comprising a substrate, a GaAs buffer layer and In which are arranged from bottom to top y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type In x Ga 1- x An As emission layer, a DBR reflection layer and an antireflection film contact layer, the p-type In x Ga 1-x The As emission layer adopts a variable component variable doping design, the In component is linearly increased from top to bottom, and the doping concentration is exponentially reduced from top to bottom; the p-type In x Ga 1-x The In component of the As emitting layer increases from 0.05 to 0.2 linearly from top to bottom, and the doping concentration is 1×10 from top to bottom 19 cm -3 Decreasing the index to 5.0X10 18 cm -3， The total thickness of the emitting layer is 1-1.3 mu m; the DBR reflection layer is formed by alternately growing two materials, namely a p-type GaAs sub-layer and a p-type AlAs sub-layer; the thicknesses of the p-type AlAs sub-layer and the p-type GaAs sub-layer satisfy the following conditions:
in n L And n H Refractive index of material of AlAs and GaAs, respectively, d L And d H The thicknesses of the AlAs and GaAs sublayers, respectively, lambda is the total reflection specifiedA center wavelength;
the thickness of the p-type AlAs sub-layer is 90nm, the thickness of the p-type GaAs sub-layer is 76nm, and the doping concentration of the DBR reflection layer is 1×10 19 cm -3 The DBR reflection layer takes a pair of AlAs/GaAs sublayers as a period, the period number of the alternate layers is not less than 3 pairs, the sublayer close to the emission layer (14) is a p-type GaAs sublayer, and the sublayer close to the antireflection film contact layer (10) is a p-type AlAs sublayer; and thermally bonding the mesa glass window on the antireflection film.
2. The near infrared response enhanced laminated composite GaAs based photocathode of claim 1, wherein the In y Al 1-y The In component of the As linear gradual change buffer layer increases from 0 to 0.22 from bottom to top, and the total thickness of the linear gradual change buffer layer is 2-3 mu m.
3. The near infrared response enhanced stacked composite GaAs based photocathode of claim 1 wherein the p-type In 0.19 Al 0.81 The 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 10 18 cm -3 。
4. The near infrared response enhanced laminated composite GaAs-based photocathode of claim 1, wherein the anti-reflection film contact layer is made of p-type GaAs material, and the doping concentration is 1×10 19 cm -3 The thickness is 300-500 nm.
5. The preparation method of the laminated composite GaAs-based photocathode based on the near infrared response enhancement of any one of claims 1 to 4 is characterized by comprising the following specific steps:
step 1, growing a GaAs buffer layer and In on a substrate In sequence y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, p-type variable component variable doped In x Ga 1-x An As emission layer, a DBR reflection layer and a p-type GaAs antireflection film contact layer;
step 2, cleaning a p-type GaAs antireflection film contact layer, depositing an antireflection film on the surface of the antireflection film contact layer, and thermally bonding a table glass window on the antireflection film;
step 3, sequentially corroding the substrate, the GaAs buffer layer and the In by using selective chemical reagents y Al 1-y As linear graded buffer layer, p-type In 0.19 Al 0.81 As corrosion barrier layer, bare emitter layer In x Ga 1-x An As surface;
step 4, performing ultra-high vacuum activation process on the p-type In x Ga 1-x Cs/O activation is carried out on the surface of the As emitting layer, so that the surface of the emitting layer covers the activating layer, and the photocathode reaches negative electron affinity.
6. The method for preparing a near infrared response enhanced laminated composite GaAs-based photocathode according to claim 5, wherein the ultra-high vacuum activation process in step 4 is specifically performed at a vacuum degree of not less than 10 -8 In the Pa ultrahigh vacuum environment, adopting a Cs/O activation process, wherein the thickness of the Cs/O activation layer is 0.5-1.5 nm.
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