CN110797240A

CN110797240A - GaAs photocathode with multilayer complex structure

Info

Publication number: CN110797240A
Application number: CN201911109780.2A
Authority: CN
Inventors: 冯琤; 宋宇飞; 张益军; 刘健; 赵静; 杨会军; 刘扬
Original assignee: Nanjing Institute of Technology
Current assignee: Nanjing Institute of Technology
Priority date: 2019-11-14
Filing date: 2019-11-14
Publication date: 2020-02-14

Abstract

The invention discloses a GaAs photoelectric cathode with a multilayer complex structure, which consists of a high-quality n-type GaAs substrate and p-type doped Ga from bottom to top_1‑xAl_xThe As buffer layer and the p-type index doped GaAs emission layer; wherein, p-type Ga_1‑xAl_xThe As buffer layer is a distributed Bragg reflection structure and consists of at least 8 pairs of GaAs/AlAs layers; the p-type index doped GaAs emission layer has a layered structure of 4 or more units, the doping concentration is distributed according to index doping, and the unit is layered from the back interface at 1.0 × 10¹⁹cm^‑31.0 x 10 of the cell layer down to the emission surface¹⁸cm^‑3. The invention can improve the emission efficiency of the GaAs photoelectric cathode by adopting the index-doped emission layer and the buffer layer of the Bragg reflection structure.

Description

GaAs photocathode with multilayer complex structure

Technical Field

The invention belongs to the technical field of preparation of semiconductor photoelectric emission materials, and particularly relates to a GaAs photoelectric cathode with a multilayer complex structure.

Background

Gallium arsenide (GaAs) photocathodes have the advantages of high quantum efficiency, concentrated energy of emitted electrons, small dark emission, large density of emitted current, and the like, and are widely used in various fields, such as low-light-level image intensifiers, polarized electron sources, solar cells, and the like. With the development of material growth technology and the aim of improving device performance, many studies based on band engineering have been made to improve spectral characteristics. In recent years, different models and structures have been proposed in which the collection efficiency of minority carriers can be increased by changing the energy band and introducing a built-in electric field inside the cathode.

Quantum efficiency is an important parameter used to evaluate the performance of photocathodes. Early proposals were made for Al_xGa_1-xAs material and Al_xGa_1-xThe energy band gradual change structure in the As/GaAs material is particularly applied to solar cells. By changing Al_xGa_1-xAl components in the As layer form energy band gradient, so that a built-in electric field is introduced to promote photoelectrons to be transported to an interface, and Al can be reduced_xGa_1-xAnd the interface between the As buffer layer and the GaAs emission layer is compounded, so that the quantum efficiency is further improved. In addition, the structure that the doping concentration is from high to low from the bulk to the surface is introduced into the GaAs emission layer, so that the photoelectric emission performance can be improved. The electron transport efficiency and the escape probability can be effectively improved by introducing the built-in electric field. In order to further improve the emission efficiency of the photocathode, the structure of the GaAs photocathode is to be further improved.

The prior art, the application number is: 2019110092093, title of the invention: variable-component variable-doping reflective Al_xGa_1-xAs/GaAs photocathode, a photocathode is disclosed, the buffer layer of which adopts Al with changed Al components_xGa_1- _xAs, Al with gradually changed composition_xGa_1-xThe As layer can reduce lattice mutation of the rear interface and simultaneously reduce the rear interfaceThe larger energy bands at the interface may form a potential barrier to electron transport to the back interface. In addition, in the case of Al of variable composition_xGa_1-xIn the As layer, Al component gradually decreases from the inside of the body to the GaAs emission layer, and a built-in electric field generated by energy band change is introduced into the buffer layer, so that photoelectrons generated in the cathode are transported to the surface of the cathode under the promotion action of the built-in electric field, and the quantum efficiency is improved. The DBR structure is formed into a periodic structure by alternately stacking two materials with high refractive index and low refractive index matched with substrate crystal lattices, so that incident light can be reflected for multiple times in a cathode body, and the absorption of incident photons is increased, and the quantum efficiency of a photocathode is further enhanced.

Disclosure of Invention

1. The technical problem to be solved is as follows:

in order to solve the technical problems, the invention provides a GaAs photocathode with a multilayer complex structure, which can realize the greater improvement of quantum efficiency in a target waveband range. The wave nature of the absorptivity that adopts Bragg reflection structure to bring in this application through the thickness on adjusting AlAs GaAs layer, can realize the more promotion of quantum efficiency in the purpose wave band scope.

2. The technical scheme is as follows:

a multilayer GaAs photocathode with a complex structure is characterized in that: the GaAs photoelectric cathode consists of an n-type GaAs substrate and a p-type doped Al from bottom to top_xGa_1-xThe As buffer layer and the p-type index doped GaAs emission layer.

Further, the p-type doped Al_xGa_1-xThe As buffer layer comprises a GaAs/AlAs layer; the GaAs/AlAs layer consists of an AlAs layer and a GaAs layer from bottom to top; the p-type doped Ga_1-xAl_xThe As buffer layer comprises at least 8 GaAs/AlAs layers; the p-type doped Al_xGa_1-xThe As buffer layer is of a Bragg reflection structure.

Further, the thickness of the AlAs layer is 45nm-55 nm; the thickness of the GaAs layer is 60nm-70 nm; the AlAs layer and the GaAs layer are both doped with uniform p-type Zn, and the doping concentration is 5 multiplied by 10¹⁸～1.0×10¹⁹cm^-3。

Further, the p-type index doped GaAs emission layer is of a layered structure; comprises at least 4 unit layers; the total thickness of the p-type index doped GaAs emission layer is 500-1500 nm; wherein Ga is doped close to p type_1-xAl_xThe unit layering of the As buffer layer is the unit layering at the rear interface, and the concentration of doped Zn is 1.0 multiplied by 10¹⁹cm^-3(ii) a A cell layer near the emitting surface and doped with Zn in a concentration of 1.0X 10¹⁸cm^-3(ii) a The p-type exponentially doped GaAs emission layer is distributed from the unit layer at the back interface to the unit layer doping concentration at the emission surface in an exponential doping manner.

3. Has the advantages that:

(1) p-type doped Ga in the invention_1-xAl_xThe As buffer layer adopts a layered structure and can be realized by the number of layers or/and the thickness of each layer according to the target waveband range.

(2) P-type doped Ga in the invention_1-xAl_xThe Bragg reflection structure of the As buffer layer is combined with the index-doped emission layer, so that the emission efficiency of the GaAs photoelectric cathode can be further improved.

Drawings

FIG. 1 is a simplified view of a multi-layer GaAs photocathode with a complex structure according to the present invention;

FIG. 2 is a diagram comparing the GaAs photocathode structure of an embodiment of the present invention with a conventional GaAs photocathode;

FIG. 3 is a graph comparing the quantum efficiency of a GaAs photocathode in an embodiment of the present invention with a conventional GaAs photocathode.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

As shown in figure 1: a multilayer GaAs photocathode with a complex structure is characterized in that: the GaAs photoelectric cathode consists of an n-type GaAs substrate and a p-type doped Al from bottom to top_xGa_1-xThe As buffer layer and the p-type index doped GaAs emission layer.

Further, the p-type doped Al_xGa_1-xThe As buffer layer comprises a GaAs/AlAs layer; the GaAs/AlAs layer is composed ofThe AlAs layer and the GaAs layer from bottom to top; the p-type doped Ga_1-xAl_xThe As buffer layer comprises at least 8 GaAs/AlAs layers; the p-type doped Al_xGa_1-xThe As buffer layer is of a Bragg reflection structure.

In the present invention, P-type doped Al_xGa_1-xThe number of layers of GaAs/AlAs layers contained in the As buffer layer can be adjusted according to the target waveband, and the thicknesses of the AlAs layers and the GaAs layers can also be adjusted according to the requirement.

The specific embodiment is as follows:

FIG. 2(a) is a schematic diagram of a GaAs photocathode with a multi-layer complex structure, which is prepared according to the flow chart shown in FIG. 1, and the GaAs photocathode is composed of a high-quality n-type GaAs substrate and p-type Al-doped Al from bottom to top_xGa_1-xThe As buffer layer and the p-type index doped GaAs emission layer.

P-type doped Al_xGa_1-xThe As buffer layer is extended on the GaAs substrate by adopting a Bragg reflection structure and consists of 10 pairs of GaAs/AlAs layers, wherein the thickness of the AlAs layer is 50nm, the thickness of the GaAs layer is 65nm, uniform doping is adopted, and the doping concentration is 1.0 multiplied by 10¹⁹cm^-3。

The P-type index doped GaAs emission layer is 4 unitsLayering with total thickness of 1000nm, each layering being 250nm, from unit layering at back interface to unit layering near emission surface, and doping concentration of 1.0 × 10¹⁹cm^-3、5.0×10¹⁸cm^-3、2.5×10¹⁸cm^-3、1.0×10¹⁸cm^-3The doping concentration of the cell layers is distributed exponentially from the cell layer at the back interface to the emitting surface.

In order to verify the quantum efficiency improvement effect of the multi-layer complex-structure GaAs photocathode, a conventional GaAs photocathode with an emission layer doped with index and a buffer layer having a fixed composition is grown, the structure is shown in figure 2(b), and similarly, the GaAs photocathode comprises a high-quality n-type GaAs substrate and a p-type doped Ga from bottom to top_1-xAl_xThe GaAs emission layer doped with p-type index is the same As the GaAs emission layer doped with p-type index. P-type doped Al_xGa_1-xThe As buffer layer is epitaxially grown on the GaAs substrate, the Al component content x is 0.7, and the doping concentration is 1.0 × 10¹⁹cm^-3。

As shown in fig. 3, a graph comparing the quantum efficiency of a GaAs photocathode with that of a conventional GaAs photocathode.

From the above, the quantum efficiency of the GaAs photocathode with the multilayer complex structure provided by the invention is higher than that of the GaAs photocathode with the traditional structure.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A multilayer GaAs photocathode with a complex structure is characterized in that: the GaAs photoelectric cathode consists of an n-type GaAs substrate and a p-type doped Al from bottom to top_xGa_1-xThe As buffer layer and the p-type index doped GaAs emission layer.

2. According to claim 1The GaAs photoelectric cathode with the multilayer complex structure is characterized in that: the p-type doped Al_xGa_1-xThe As buffer layer comprises a GaAs/AlAs layer; the GaAs/AlAs layer consists of an AlAs layer and a GaAs layer from bottom to top; the p-type doped Ga_1-xAl_xThe As buffer layer comprises at least 8 GaAs/AlAs layers; the p-type doped Al_xGa_1-xThe As buffer layer is of a Bragg reflection structure.

3. The GaAs photocathode with a multilayer complex structure as claimed in claim 2, wherein: the thickness of the AlAs layer is 45nm-55 nm; the thickness of the GaAs layer is 60nm-70 nm; the AlAs layer and the GaAs layer are both doped with uniform p-type Zn, and the doping concentration is 5 multiplied by 10¹⁸～1.0×10¹⁹cm^-3。

4. The GaAs photocathode with a multilayer complex structure as claimed in claim 1, wherein: the p-type index doped GaAs emission layer is of a layered structure; comprises at least 4 unit layers; the total thickness of the p-type index doped GaAs emission layer is 500-1500 nm; wherein Ga is doped close to p type_1-xAl_xThe unit layering of the As buffer layer is the unit layering at the rear interface, and the concentration of doped Zn is 1.0 multiplied by 10¹⁹cm^-3(ii) a A cell layer near the emitting surface and doped with Zn in a concentration of 1.0X 10¹⁸cm^-3(ii) a The p-type exponentially doped GaAs emission layer is distributed from the unit layer at the back interface to the unit layer doping concentration at the emission surface in an exponential doping manner.