Effect of Polarity on Photoelectrochemical Properties of Polar and Semipolar GaN Photoanode

Abstract

In this study, the photoelectrochemical (PEC) properties of polar GaN were compared to those of semipolar GaN. GaN samples were grown on sapphire by metal–organic chemical vapor deposition (MOCVD). Various electrolytes, namely, aqueous solutions of H2SO4 (pH 0.2), Na2SO4 (pH 6.0), and NaOH (pH 14.0), were used for investigating the effect of pH. The band-edge potentials of polar and semipolar GaN calculated from the Mott–Schottky plots indicates that these potentials can split water and followed the Nernst equation for each electrolyte. Further, the PEC properties of GaN with different polarities were investigated under 100 mW illumination. The photocurrent density of polar GaN was found to be higher than that of semipolar GaN. This result was attributed to the polarization effect of polar GaN. Interestingly, all GaN samples showed a divergent trend in the two-electrode method, similar to a real device.