First Principles Research On Opto-electronic Properties Of Al_xGa_1-xAs Photocathode

Low Level Light?LLL?night vision technology devotes to explore access to information acquisition,conversion,enhancement,recording and display of object images during the period of night and other low light image,which can effectively extend human vision in the domain of time,space and frequency.LLL night vision technology has been applied to night-time reconnaissance,targeting,vehicle driving,photoelectric fire-control and other battlefield operations.LLL image intensifier is the core of low-light level night vision device,and photocathode is the key devices of LLL image intensifier,thus photocathode materials have gained a research hotpot.Negative electron affinity gallium aluminum arsenide(Al_xGa_1-xAs)photocathodes owns an important application prospect for ocean detection and marine communication.However,theoretical research on Al_xGa_1-xAs is incomplete and needs to explore further.Using the first principles calculation method,the opto-electronic properties of NEA Al_xGa_1-xAs materials are researched systematically from atomic level,the results have reference value on experimental research.The main contents are shown as following:1.The opto-electronic properties of Al_xGa_1-xAs bulk material were researched.The characteristics of band structure,density of states,absorption spectrum and so on were calculated and discussed.Combine microscopic electronic structure with optical characteristics is the main basis for the analysis of crystal band structure and optical properties,and it is important means to investigate new semiconductor materials simultaneously.2.The influence on opto-electronic properties of Zn doping at surface and Al_xGa_1-xAs bulk with different Al constituent were researched and discussed.Due to the activation process was always completed on P type surface,the use of Zn doping at surface was proposed.The variations of overall structure stability with Zn doping at different sites were discussed,the results pointed out the better P-type semiconductor model.Meanwhile,the formation energy,stability and band structure of Al_xGa_1-xAs photocathode material with different Al constituent were investigated and discussed.The results play an important role in application of photocathode materials.3.In order to study the activation mechanism,the first stage “Cs adsorption” process during the period of activation for Al_xGa_1-xAs photocathode material was researched and compared with GaN and AlGaN photocathode.GaN?0001?and Al_0.25Ga_0.75N?0001?surfaces were recognized as contrast surfaces.The adsorption of Cs/Al_0.5Ga_0.5As?001??₂?2×4?,Cs/GaN?0001?and Cs/Al_0.25Ga_0.75N?0001?surfaces were built and investigated,the “yo-yo” activation process was simulated.The adsorption energies,work function and surface dipole moments of Cs adsorbed on three surfaces were calculated and discussed.The photocurrents during activation process were recorded by multi-information measurement system in situ,and the results could provide supporting and guiding significance on preparation process.