The electronic structure and optical properties of pure and P-doped cubic-blende gallium arsenide (GaAs) for different P constants (x=0, 0.125, 0.25, 0.375) have been studied by the first-principles projected augmented plane potential approach based on the density functional theory and the generalized gradient approximation method. It shows that the P-doped material has a smaller lattice constant, which resulted in a local lattice distortion. The minimum of the conduction band moves to high energy level and the band gaps gradually become wide with gradual increase concentration of P impurity. The dielectric function are calculated based on Kramers-Kroning relations. The optical property studied from the calculated absorption coefficients shows that the adsorption peaks change obviously in the visible light wavelength area for the P-doped GaAs system.
In order to solve the sensitivity’s degression in the GaAs NEA photocathode, our crew dissected the Gen. III Low-Light-Level（L-L-L）tube and analyzed the residual gas from the tub e while functionally operating via mass spectrometer. The photoemission-harmful gas like C，CO，CO2 were the principal reason cause the photocathode sensitivity to drop most. Applying the theory of dipole layer, this paper had this thorough discussion over the impact the residual pernicious gas had upon the photocathode. The residual gas on the emission layer enlarged the interface barrier and dwindled the chance of overflow about the same time.There were none photoemission when the single molecule gas were all over the emission layer, and so the life-span has came to an end as well. Our crew bring forward “carbon-contamination precaution measure” on account of lo wering potential barrier, which resolve problems like unstable photocathode sensitivity and limited life-span.