Three-dimensional transportation mechanism of transmission-mode AlGaN nanoarray photocathode within four steps from photon excitation to electron collection

This study focuses on the photoemission model of transmissive AlGaN nanoarray cathodes. By introducing energy-dependent absorption coefficient and a new calculation method upon escape probability of photoelectrons, we establish a three-dimensional transmissive photoemission model. Based on the photoemission model, the influences of multiple parameters (geometric, surface, environmental, material) on cathode performance are explored. It is found that the quantum efficiency (QE) attains a better response with high-energy photons irradiated. When the height of the nanoarray is 90 nm and the diameter is 60 nm, the QE generates a high response up to 24.6 % and 22.4 %. When the external electric field is less than 1 V/μm, the enhancement of the external electric field can improve the effective quantum efficiency (EQE), especially when low-energy photons less than 4 eV are incident. The increase of Al composition from 0 to 1 lead to an increasing response threshold of EQE from 3.4 eV to 6.3 eV. Al_xGa_1-xN array cathodes with different Al compositions all exhibit the highest EQE near the threshold. This study provides a new theoretical basis and computational idea for development of the transmissive photocathode with nanoarray structure.