Probing the surface oxidation process in hexagonal boron nitride epilayers

Thermal neutron detectors based on hexagonal boron nitride (h-BN) epilayers have demonstrated a record high efficiency among solid-state detectors at 58%. It was found that the performance of h-BN detectors is profoundly influenced by charge recombination at the surfaces. The dynamic process of surface oxidation in h-BN epilayers has been probed by x-ray photoelectron spectroscopy. The spectra of high-resolution (0.1 eV) scans indicated that the linewidth of the B 1s peak at 190.6 eV increased and the peak intensity decreased with an increase in exposure time in-air (tair). The main B 1s peak at 190.6 eV evolved into multiple peaks at a higher binding energy position due to oxygen impurities tending to occupy nitrogen sites and form the B–O bond. Time constants of the oxidation process have been determined, revealing that the formation process of the B–O bond is very fast and within minutes in h-BN. The results suggest that reducing nitrogen vacancy generation during growth and employing surface treatment techniques would further improve the performance of h-BN devices.