Impact of oxygen plasma power on the performance of Ga2O3 passivated GaN ultraviolet photodetectors

Abstract

The role of oxygen plasma power on the extent of surface passivation of Gallium Nitride (GaN) epitaxial layers and the photo-response of Au/Ni/GaN Schottky detectors is investigated. The surface morphology is found to be preserved in oxide passivated GaN at intermediate plasma power which significantly deteriorates at higher power. The photoluminescence spectrum shows a fall in the intensity of band edge and defects related yellow luminescence at higher power indicating the generation of non-radiative recombination centres. The chemical and electronic structures of the passivated layer investigated by x-ray photoelectron spectroscopy revealed the formation of stoichiometric Ga2O3 up to intermediate plasma power and partial decomposition of Ga2O3 along with formation of gallium sub-oxides at higher power. This leads to an enhancement in the responsivity of the photodetector after passivation at an intermediate plasma power followed by a considerable reduction at higher power. From the electrical transport measurement across the Au/Ni/GaN Schottky diode, it is observed that the diode manifests more Schottky (Ohmic) character after oxygen plasma treatment at intermediate (higher) power. The present investigations provide a clear guideline on the selection of oxygen plasma power for surface passivation on GaN, which is highly beneficial in optimizing the performance of GaN-based optoelectronic and power devices.