Electron energy and angle distribution of GaAs photocathodes

A precise Monte Carlo model is developed to investigate the electron energy and angle distribution of the transmission-mode GaAs (100) photocathode at room temperature. Both distributions are important for high-quality electron sources. The results show that the energy loss (0.1309 eV) and the angle-dependent energy distribution curves fit well with experimental data. It is found that 65.24% of the emission electrons come from Γ valley, 33.62% from L valley, and 1.15% from X valley. The peak of the energy distribution curve is contributed by both Γ and L-valley electrons, while the high-energy part is contributed by Γ-valley electrons rather than L electrons, which is different from previous inference and can be attributed to the narrow energy range of L-valley electrons. However, L-valley electrons have a larger angular spread than Γ-valley electrons and lead to the spread of the emission cone. The further simulation indicates that increasing the hole concentration or the thickness of the first activation layer can improve the angle distribution, but the energy distribution will turn to be slightly more dispersive. Temperature effect on the two distributions is also analyzed. The energy distribution curve moves towards the higher energy while the angle distribution curve moves towards the lower value when the temperature declines.