Damage Characteristics of n-GaN Crystal Etched with N₂ Plasma by Soft X-Ray Absorption Spectroscopy

Abstract

n-GaN crystals were plasma-etched with N₂ gas, and their surfaces were analyzed mainly by X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (XAS). In the samples etched with a high self-bias voltage of −400 V, the surface morphology changed, roughening under the treatment conditions of higher gas pressures (∼100 mTorr) and longer treatment times (∼200 min). In these samples with a roughened surface, the N/Ga composition ratios measured by XPS deviated greatly in the Ga-rich direction from the normal N-preferentially etched sample. Moreover, N-K near-edge X-ray absorption fine structure (NEXAFS) spectra changed greatly from that normally observed in GaN crystals. New peak features were also observed in the O 1s XPS and the O-K NEXAFS spectra. The surface roughening, the composition deviation, and the anomalous spectra in XPS and the NEXAFS correlated well with each other, which indicated the formation of another compound in the surface-roughened sample. [DOI: 10.1380/ejssnt.2016.9]