Comparative study on the influence of Al component at GaAlAs layer for GaAs/AlGaAs photocathode*

We designed two transmission-mode GaAs/AlGaAs photocathodes with different Al x Ga 1- x As layers, one has an Al x Ga 1- x As layer with the Al component ranging from 0.9 to 0, and the other has a fixed Al component 0.7. Using the first-principle method, we calculated the electronic structure and absorption spectrum of Al x Ga 1- x As at x =0, 0.25, 0.5, 0.75 and 1, calculation results suggest that with the increase of the Al component, the band gap of Al x Ga 1- x As increases. Then we activated the two samples, and obtained the spectral response curves and quantum efficiency curves; it is found that sample 1 has a better shortwave response and higher quantum efficiency at short wavelengths. Combined with the band structure diagram of the transmission-mode GaAs/AlGaAs photocathode and the fitted performance parameters, we analyze the phenomenon. It is found that the transmission-mode GaAs/AlGaAs photocathode with variable Al component and various doping structure can form a two-stage built-in electric field, which improves the probability of shortwave response photoelectrons escaping to the vacuum. In conclusion, such a structure reduces the influence of back-interface recombination, improves the shortwave response of the transmission-mode photocathode.