Stability Study Of GaAs Photocathode Based On The First Principle

Low-light level (LLL) night vision equipment can achieve light-electricity conversion, amplification, imaging and other processes very quickly in low light environment. Therefore, it is wildy applied in various fields, and becomes a hot topic on photoelectric materials in the 21st century. The third generation of LLL image intensifier takes the negative electron affinity GaAs as the core material and greatly expands the range of visibility and long-wave threshold, therefore, it has been widely used in low-light level night vision field.After years of hard work,technicians in the low-light level night vision field have established perfect GaAs photocathode and manufacturing system, but it still lags behind international level in terms of specific performance. Besides, in terms of device life, GaAs cathode surface can easily be contaminated by impurity gas, The impurity gas will drastically reduce the performance of the photocathode. This dissertation focuses on the stability of the GaAs photocathode and conducts a comprehensive study. The main contents are listed as follows:1. The working principle of photocathode and the formation of GaAs photocathode, as well as the preparation process of GaAs photocathode. By comparing foreign and domestic researches, it presents the main research contents and direction, and illustrates the purpose and significance of the study.2. We study the surface model of GaAs photocathode from the oretical perspective, we build a variety of GaAs photocathode cluster models and cesium oxygen activated layer cluster models. Then, a detailed introduction to density functional theory has been presented.Weselects appropriate density functional methods basis sets according to the established model. As a result, we provides theoretical basis for the first-principles calculation of GaAs photocathode.3. The computational methods and software are introduced, we select Orca program package as the computational software for the present study.4. Simple cluster model and density functional theory are adopted to study the interaction between various impurity gases with the Cs11O3 cluster model, The results indicate that H2O has a very high binding energy,and water vapor should not exist in the manufacture and usage of The GaAs photocathode. Meanwhile, density functional theory is used to calculate the adsorption and dissociation process of the CH3OH molecule and H2O molecule on the Ga-Rich GaAs(001)-(4×2). The results show that the CH3OH surface molecule will firstly form two chemical adsorption states on the surface of Ga-Rich GaAs(001)-(4×2). After dissociation,CH3OHwill generate CH3O radical and H atom, which will be adsorbed on different positions of the surface. By comparing various adsorption and dissociation paths, it is found that the dissociated H atom can easily be adsorbed by adjacent As atom on the second layer of the surface. Similarly, the H2O molecule will form a chemically adsorbed state on GaAs surface, the adsorption position of the dissociated atom and radical is similar to those of CH3OH, that is, the H atom is more likely to be adsorbed by the adjacent As atom on the second layer of the surface.5. A summary of this dissertation has been presented, and We have proposed some existing problems and corresponding recommendations.