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GaAs material has excellent photoelectric properties and is the most sensitive vacuum semiconductor material in the visible light band. GaAs photocathode has become the core component of low-light-level night vision device and been widely used in the field of low-light-level night vision. We systematically analyzed the structural characteristics of the low-light image intensifier and defined the boundary conditions of GaAs electron emission. It provided calculation basis for further analysis of the photoelectric effect of GaAs photocathode. We established GaAs crystal model on first-principle, calculated the energy band structure, and analyzed the mechanism of surface electrons escaping. After photon energy transferring to the electronic, electrons were excited and went out of its orbit, becoming free electrons and gaining initial kinetic energy. According to the experience, we assumed the collision energy loss rate after free electron diffusion process, and calculated number of electron collision in crystal model and displacement distance. Linear displacement distance is electron diffusion length. The initial kinetic energy of electrons excited by GaAs material depends on the energy of incident photons, as well as on the cathode's own temperature. We analyzed the relationship between the electron diffusion length of the material and the temperature. The electron emission characteristics of GaAs material were summarized, which provided technical support for the subsequent process research of this cathode material. GaAs low light image intensifier is made of the following parts: photocathode、 MCP、 screen and high voltage power. Using the elastic collision model, we calculated the energy of the photon transported to the electron transfer. Assuming the collision energy loss rate of electronic diffusion is 20% every time, free electrons crash until photon energy losses. The collision frequency and the moving distance are GaAs material properties. We analyzed the relationship between the temperature and electron diffusion length of GaAs in this paper.
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