Progress of Theoretical Research on the Related Scientific Problems of NEA GaN
Photocathode
Ma Jun
School of Information Science and Engineering
University of Jinan
Jinan, China
e-mail: 792962011@qq.com
Fu XiaoQian
School of Information Science and Engineering
University of Jinan
Jinan, China
e-mail: ise_fuxq@ujn.edu.cn
Yang MingZhu
School of Physics and Optoelectronic Engineering
Nanjing University of Information Science and
Technology
Nanjing, China
e-mail: 921887061@qq.com
Zhao He
School of Information Science and Engineering
University of Jinan
Jinan, China
e-mail: 511896604@qq.com
Abstract—In order to deeply analyze the emission mechanism
of NEA(Negative electron affinity) GaN photocathode,further
improve its performance, design and demonstrate the key
parameters of the solar-blind ultraviolet AlGaN photocathode ,
this paper summarizes the application and calculation results
of first-principles calculation in the above research.The
importance of the combination about theoretical calculation
and experimental results in the research is expounded, and the
application of this method in future research is prospected.
Keywords-negative electron affinity; GaN photocathode;
solar-blind ultraviolet; first principles
I. INTRODUCTION
NEA GaN(Negative Electron Affinity) photocathode ,as
the main detection unit of ultraviolet vacuum detector, has an
important impact on the performance of the detector .At
present , the experimental research of NEA GaN
photocathode has reached a high level. The reflective
quantum efficiency can reach more than 70 percent and the
transmission quantum efficiency can reach more than 30
percent.[1-6]Based on this, a single photon detector has been
published.[7]In order to further improve the quantum
efficiency, stability of NEA GaN photocathode and prepare
high-performance "solar blind" detector on this basis, besides
experimental research[8-9], we need to use theoretical
calculation method to predict the performance of the
photocathode and further verify the existing experimental
results. On the one hand ,by combining the calculated results
with the experimental results, a complete system of mutual
verification can be formed to better explain the scientific
problems. On the other hand, theoretical prediction of the
key parameters restricting the performance of photocathodes
can be made before the experimental study, shortening the
research cycle, saving research funds and improving the
efficiency of the research.This paper is mainly divided into
six parts: introduction, theoretical basis, first principles
calculation and results analysis of undoped GaN materials,
influence of doping on the structure and properties of NEA
GaN, first-principles calculation and simulation of Cs/O
activation of reflective NEA GaN photocathode, conclusion
and prospect. For the first-principles calculation and result
analysis of undoped GaN materials, the energy band
structure, optical properties and density of states are
reviewed in detail. As for the influence of doping on the
structure and properties of NEA GaN, this part mainly
reviews the comparison about the results of undoped,
looking for the best P-type doping method and analyzing the
various properties of GaN after doping. First-principles
calculation and simulation of Cs/O activation of reflective
NEA GaN photocathode are mainly concerned with the
study of Cs/O adsorption on various models and the variation
of surface work function. In this paper, the first-principles
calculation results of NEA GaN and AlGaN photocathodes
are summarized and their characteristics are described.
Finally, the further application of the method in UV
photocathode is prospected.
II. THEORETICAL BASIS
For the calculation of quantum mechanics, the theoretical
basis is to solve the Schrodinger equation. But the equation
can’t be directly solved. The adiabatic approximation of
Born-Oppenheimer[10-12]is applied to the equation, and the
equation is simplified. Later, the Hartree-Fock
approximation [13-14] proposed by B.A. Fock and J.C.
Slater on the basis of Hartree approximation further
improved the equation and improved its accuracy. In 1964,
Hobenberg and Kohn perfected the theory, obtained
Hohenberg-Kohn theorem [15] and applied it to Schrodinger
equation. In the 1960s, Kohn and Sham proposed the Kohn-
Sham scheme [16]. The first two of the three functions in the
Hohenberg-Kohn theorem, namely the kinetic energy term
function and Kulun force function, are given in concrete
form. Exc [p (r)], the third function of exchange correlation
energy which is not solved in theory, can be solved by local
density approximation [17-18] (LDA) and generalized
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2019 2nd International Conference on Electronics Technology
978-1-7281-1617-4/19/$31.00 ©2019 IEEE