Theoretical Study On Properties Of Al_xGa_1-xN Photocathode With Multilayer Material

Low level light?LLL?night vision technology is used to solve the problems of low light and dark night when the image capture,which can present a clear image in human eyes.Making the human eyes extension on the time domain,spatial and frequency domain.LLL is now used in night detection,vehicle driving and other fields.The multi-layer structure of the photocathode is an important part for the LLL night vision probe.Thus the research and analysis of photocathode with multi-layer structure not only has practical value,but contribute to the development and progress of LLL night vision technology.Nowadays,the negative electron affinity?NEA?of AlGaN photocathode is widely used in ocean communication,ocean detection and space exploration.However,the research on the multi-layer structure of AlGaN photocathode is not perfect,and further theoretical analysis is needed.This paper focuses on the theoretical analysis of the multi-layered AlGaN photocathode characteristics by using the analysis method of the first principle.The main contents of the study including:1.Using of Materials Studio software to simulate the Al_0.125Ga_0.875N?Al_0.25Ga_0.75N?Al_0.375Ga_0.625N?Al_0.5Ga_0.5N supercell models with wurtize structure.Applying the method of the first principle based on quantum mechanics to calculate the electronic structure and optical properties of Al_0.125Ga_0.875N,Al_0.25Ga_0.75N,Al_0.375Ga_0.625N,Al_0.5Ga_0.5N supercell.The results show that the band gap width of Al_xGa_1-xN is increasing with Al component increasing,and the wavelength is getting shorter and shorter.With the increasing of the Al component the conduction band moves to high energy region,and the Fermi energy slightly moves to the top of valence band,which can lead to the bigger Al component is,the weaker the conductivity of Al_xGa_1-xN is.The absorption spectrum moves to the high energy direction.That is to say,the photoeletric performance can be adjust by incorporation of a certain proportion of Al.This research is helpful for the application of GaN-based photoemission materials.2.By using MOCVD method to grow two kinds of reflective AlGaN photocathodes:one is the Al component of active layer of photocathode ranges 0.5 to0 from the body to the surface,and another is the emission layer has fixed Al composition with 0.25.The quantum efficiency and spectral response of the two multi-layer photocathodes structure were measured by the multi-information measurement system.Results show that the photocathode with varied Al component has better quantum efficiency and spectrum response than that of photocathode with fixed Al component.There is a built-in electric field in the emission of multi-layer photocathode with the varied Al component,while has no in the emission of multi-layer photocathode with the fixed Al component.3.Through employing the Materials Studio software to simulate Mg atoms substitution doping and interstitial doping in Al_0.25Ga_0.75N structure model.The analysis and calculation of the two model's electronic structure and optical properties.Result shows that Mg atom substitution doping makes Al_0.25Ga_0.75N present the p-type property,and Mg interstitial doping in Al_0.25Ga_0.75N presents the n-type feature.In a word Mg substitution doping has higher absorption coefficient,lower reflectivity and lower energy loss than Mg interstitial doping.