Electric-field-induced band bending on GaN: in situ effects of electron beam irradiation on time-dependent cathodoluminescence

Electron beam bombardment of GaN has been monitored by secondary electron (SE), cathodoluminescence (CL) imaging, simultaneous in situ CL, and specimen current (SC) measurements. Under extreme irradiation conditions, system perturbations, as seen by SE and time-dependent CL, are attributed to internal charge dynamics extending beyond the scanned areas. Under moderate irradiation conditions, the size of affected regions correlates with nominal scanned regions. Time-dependent CL at the near band edge (NBE) revealed complex interplay with SC, which was modeled through band bending at the Au/GaN interface. The system has shown distinctive internal electric field dynamics upon sample handling, affecting both time-dependent CL spectra and SC as well as producing contrast reversal in SE imaging, to which humidity adsorption could be contributing. The band-bending model presented here can account for both moderate irradiation and humidity effects through variations of depletion widths and Schottky barrier heights. Our findings are consistent with current models where e-beam activated VGa promotes decreased NBE intensities and CN promotes DL emissions.