Influence of wet chemical etching on electronic structure and optical response of polar (0001) GaN films

Abstract

We report the influence of molarity dependent wet chemical KOH etching on the optical response and near surface band structure of highly crystalline polar (0001) GaN films. Morphological evolutions from a highly smooth to a granular like surface in nano-regime was witnessed with increment in etchant (KOH) concentration. X-Ray photoemission spectroscopy analysis divulged a shift towards lower binding energy associated with upward band bending and indicated the elimination of surface states along with fermi level pining near the charge neutrality level. Photoluminescence studies exhibited a strong near band edge emission centred at 3.41 eV and a defect related broadband ranging from 1.8 eV to 3.2 eV. It was observed that chemical etching leads to drastic reduction in the defect band (from 63% to 16%) with increased KOH concentration. Further, in-depth analysis of luminescence associated with defect states, vacancies, donor/acceptor states was performed to develop a better understanding of the observed results. The study demonstrates that chemically etched films pursue superior material properties which could be utilised for the development of GaN based high performance devices requiring higher surface area i.e. sensors and detectors.