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 (000-1) face (N-face) of free-standing n-type GaN with a carrier concentration of 1× 10¹⁸ 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. [DOI: 10.1380/ejssnt.2009.847]