Flat-band potentials of Ga-face and N-face in free-standing n-GaN electrode and their effects on water electrolysis

Abstract

The flat-band potentials of (0001) face (Ga-face) and (0001) face (N-face) of free-standing n-type GaN with a carrier concentration of 1×10 18 cm-3 are measured by the bias dependence of photoluminescence intensity in electrolyte solution. The flat-band potentials of Ga-face and N-face are -1.5±0.1 V and -1.2±0.1 V in 0.1 molL -1 Na2SO4 solution (pH7) on the basis of Ag/AgCl reference electrode, indicating the conduction band edge of N-face is about 0.3 eV lower than that of Ga-face. This result is consistent with the observation that the H2 gas generation occurs vigorously on N-face compared with Ga-face when the free-standing n-GaN electrode is at a fixed bias of -1.8 V vs. Ag/AgCl. © 2009 The Surface Science Society of Japan.