Exploring optoelectronic properties of C-doped GaAs for photocathode application from first-principles calculation

In the preparation process of negative electron affinity GaAs photocathodes, the p-type doped property is beneficial to photoemission, and the doping element is usually Be or Zn. In fact, C-doped GaAs material has been widely used due to its high activation rate, extremely low diffusion coefficient, and good thermal stability, whereas the influence mechanism of the C dopant on the performance of the GaAs photocathode is still unclear. In order to investigate the substitutional effect on C-doped GaAs, electronic structures and optical properties along with angular distribution of emitted photoelectrons are obtained by utilizing first-principles calculation based on density functional theory. The results show that C-doped GaAs is more likely to form a p-type doped feature in which the C dopant forms new levels in the forbidden band and reduces the energy gap as well as increasing the absorption coefficient and decreasing the reflectivity in the visible light band. In addition, the electrons emitted from the Γ-valley for C-doped GaAs have better directivity than those for pure GaAs, which is mainly ascribed to the smaller effective electron mass in the Γ-valley.