Comparative research for GaAs photocathodes with graded compositional AlxGa1−xAs buffer layer

Abstract

The graded Al compositional structure design in AlxGa1−xAs buffer layer can well increase the quantum efficiency than the stationary Al compositional structure design, especially at short-wave band. For deep study, the samples of two structures were prepared by metal organic chemical vapor deposition for carrying out the comparative research between surface photovoltage before Cs–O activation and spectral response current after Cs–O activation. Through fitting calculations and analyzes, the mixed structure of graded Al composition in AlxGa1−xAs buffer layer and exponential doping concentration in GaAs active layer cannot only form continuous internal electric field throughout window layer and active layer, but also decrease the misfit dislocations and stacking faults arising from lattice mismatch at the AlxGa1−xAs/GaAs interface. The better interface properties can further decrease the back interface recombination velocity than the standard structure design. Furthermore the continuous internal electric field can well increase the electron diffusion and drift length for active layer and surface escape probability for surface barriers and can also drive more photo-excited electrons at short-wave band in buffer layer to cathode surface.