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CN-121983482-A - GaN photocathode based on AlGaN transition layer

CN121983482ACN 121983482 ACN121983482 ACN 121983482ACN-121983482-A

Abstract

The invention discloses a GaN photocathode based on an AlGaN transition layer, which sequentially comprises a substrate, an AlN layer, a GaN emission layer, a Cs/O activation layer and an AlGaN transition layer arranged between the AlN layer and the GaN emission layer from bottom to top. According to the invention, the AlGaN transition layer is arranged between the AlN layer and the GaN layer, and the forbidden band width of the AlGaN material can be changed from 3.42eV to 6.2eV along with the change of the Al component. While the lattice constant of AlGaN can be continuously controlled by Al composition, and the lattice constant is intermediate between AlN and GaN. The AlGaN transition layer is inserted to convert the original abrupt mismatch of AlN-GaN into gradual mismatch of AlN-AlGaN-GaN, so that a part of stress is released at the AlGaN transition layer, the stress is reduced to be transferred to the GaN emission layer above, and the crystal quality of the GaN emission layer is improved.

Inventors

  • WANG KE
  • LIU DAWEI
  • LIU YU
  • YAO QI
  • XU JIANQIAO
  • LU HAI
  • ZHANG RONG

Assignees

  • 南京大学
  • 合肥国家实验室

Dates

Publication Date
20260505
Application Date
20260210

Claims (8)

  1. 1. The utility model provides a GaN photocathode based on AlGaN transition layer, its structure includes from bottom to top in proper order: A substrate; An AlN layer; A GaN emission layer; A Cs/O activating layer; the AlGaN light emitting diode is characterized in that an AlGaN transition layer is further arranged between the AlN layer and the GaN emission layer.
  2. 2. The GaN photocathode of claim 1 wherein the AlN layer has a thickness of 0.1-5 μm.
  3. 3. The GaN photocathode of claim 1 wherein the GaN emission layer is p-type doped, has a thickness of 50-200nm and a Mg doping concentration of 3e18-5e19cm -3 .
  4. 4. The GaN photocathode of claim 1 wherein the Cs/O active layer is on the order of nm thick.
  5. 5. The GaN photocathode of any one of claims 1 to 4, wherein the AlGaN transition layer is AlxGa1-xN having a uniform composition, wherein 0< x <1, and a thickness of 0.1 to 1 μm.
  6. 6. The GaN photocathode of any one of claims 1 to 4, wherein the AlGaN transition layer is AlxGa1-xN with gradually changed Al components, wherein 0< x <1, the closer to the AlN layer, the higher the Al component content is, and the thickness is 0.1-1 μm.
  7. 7. The GaN photocathode of any one of claims 1 to 4, wherein the AlGaN transition layer adopts an AlGaN superlattice structure, and has a thickness of 0.1 to 1 μm.
  8. 8. The GaN photocathode of claim 7 wherein the AlGaN superlattice structure comprises a bottom layer structure, an intermediate structure and a top layer structure, wherein the bottom layer structure circulates Al 0.8 Ga 0.2 N at 5nm and GaN at 3nm for 4 periods, the intermediate structure circulates Al 0.3 Ga 0.7 N at 10nm and GaN at 3nm for 4 periods, and the top layer structure circulates Al 0.1 Ga 0.9 N at 15nm and GaN at 3nm for 4 periods.

Description

GaN photocathode based on AlGaN transition layer Technical Field The invention relates to a GaN photocathode based on an AlGaN transition layer, and belongs to the technical field of semiconductor materials. Background The semiconductor photocathode is used as an important element for photoelectric conversion and has wide application in the field of vacuum optoelectronic devices. The vacuum photoelectric device has the advantages of high gain, low noise, high response speed and the like, and is widely applied to ultra-weak and ultra-fast changing optical radiation detection, imaging of a radiation target which is invisible to naked eyes or has low brightness and the like. Currently, photocathodes are mainly used in photomultiplier tubes, fringe image transformers, image intensifiers, electron-bombarded CMOS and electron emission sources of electron microscopes. Among them, photomultiplier (photomultiplier tube, PMT) has been widely used in spectroscopic analysis instruments, environmental detection instruments, medical diagnostic instruments, and the like. The photoelectron emission of the negative electron affinity (Negative electron affinity, NEA) GaN photocathode mainly comprises three steps, namely 1, photoelectron excitation, wherein electrons in a valence band of a GaN material are excited to be transited into a conduction band. 2. Transportation of photogenerated carriers photoelectrons excited to the conduction band are transported to the surface by diffusion. 3. And the emission of carriers, namely, due to the negative electron affinity state of the surface of the photocathode, photoelectrons can escape into vacuum only by passing through a surface potential barrier through a tunneling effect without additional energy for transporting to a vacuum energy level. The current development state of industry and defect reasons are that the quantum efficiency of the GaN photocathode is mainly influenced by material crystal quality, structure optimization and the like. The conventional GaN photocathode is to directly epitaxially grow a GaN emission layer on AlN and p-type dope the GaN emission layer. There is a problem of natural lattice mismatch due to the GaN lattice and AlN lattice. Too large a thickness of p-type GaN may cause a case where the GaN emission layer is fully relaxed, which may cause a problem of a rapid increase in dislocation density. These dislocations can become recombination centers and scattering centers for holes, and present a significant challenge to the crystal quality of the GaN emissive layer, etc. Disclosure of Invention The invention aims to provide a GaN photocathode based on an AlGaN transition layer, wherein the AlGaN transition layer is inserted between a GaN emission layer and an AlN layer, so that the dislocation density of p-type GaN can be remarkably reduced. The aim of the invention is achieved by the following technical scheme: the utility model provides a GaN photocathode based on AlGaN transition layer, its structure includes from bottom to top in proper order: A substrate; An AlN layer; A GaN emission layer; A Cs/O activating layer; an AlGaN transition layer is arranged between the AlN layer and the GaN emission layer. Preferably, the AlN layer has a thickness of 0.1-5. Mu.m. Preferably, the GaN emission layer is doped p-type, the thickness is 50-200nm, and the doping concentration of Mg is 3e18-5e19cm -3. Preferably, the Cs/O activation layer thickness is on the order of nm. Preferably, the AlGaN transition layer is AlxGa1-xN with uniform components, wherein 0< x <1, and the thickness is 0.1-1 mu m. Preferably, the AlGaN transition layer is AlxGa1-xN with gradually changed Al components, wherein 0< x <1, the closer to the AlN layer, the higher the Al component content is, and the thickness is 0.1-1 mu m. Preferably, the AlGaN transition layer adopts an AlGaN superlattice structure, and the thickness is 0.1-1 mu m. Preferably, the AlGaN superlattice structure comprises a bottom layer structure, an intermediate structure and a top layer structure, wherein the bottom layer structure is formed by circulating 5nm of Al 0.8Ga0.2 N and 3nm of GaN for 4 periods, the intermediate structure is formed by circulating 10nm of Al 0.3Ga0.7 N and 3nm of GaN for 4 periods, and the top layer structure is formed by circulating 15nm of Al 0.1Ga0.9 N and 3nm of GaN for 4 periods. According to the GaN photocathode disclosed by the invention, the material above the substrate is AlN, the forbidden bandwidth of the GaN photocathode is 6.2eV and is larger than the forbidden bandwidth of GaN by 3.42eV, on one hand, electrons can be prevented from diffusing to the substrate, and on the other hand, the built-in electric field formed by the heterojunction interface can promote the electrons of GaN to move to the surface of the photocathode. However, the lattice constant of AlN is not matched with that of GaN, and GaN is easily fully relaxed by directly growing GaN on an AlN layer, so that the