In recent years, III-nitride materials – traditionally used in light-emitting diodes, high power and high temperature electronic devices and short-wavelength photodetectors - have attracted considerable interest in photo-electrochemistry and photocatalysis due to the very favorable energy position of its band edges with respect to many redox levels in liquid electrolytes.

Understanding the mechanisms governing charge transfer across the semiconductor/electrolyte interface is important for a quantitative analysis of cyclic voltammetry and impedance spectroscopy. In previous work [1], by combining contact potential difference and photocurrent measurements, we could show that localized surface defect states play a crucial role in the kinetics of photo-generated charges. As a next step, the influence of these electrically active states located in the semiconductor bandgap on the charge transfer to the electrolyte is investigated.

Here, we present a systematic electrochemical study of MOCVD grown n-type GaN in aqueous electrolytes. Cyclic voltammetry and impedance spectroscopy measurements are performed over a wide range of potentials and frequencies to determine the energy positions of GaN charge transfer states and to investigate the electron transfer kinetics between GaN and redox molecules. Furthermore, the surface states are changed by applying different surface treatments and the influence of these on the details of charge transfer is investigated.

[1] A. Winnerl, R. N. Pereira, and M. Stutzmann, Phys. Rev. B 91, 075316 (2015)