Electrochemical properties of GaN nanowire electrodes—influence of doping and control by external bias

We report on the electrochemical characteristics of GaN nanowire (NW) ensembles grown by plasma-assisted molecular beam epitaxy on Si(111) substrates and on the influence of Si and Mg doping. The NW electrochemical properties in terms of surface capacitance (CS), surface resistance (RS) are extracted from electrochemical impedance spectra. While Mg doping of GaN NWs does not cause a significant variation of these quantities, an increase of the Si concentration leads to an increase of CS and a simultaneous decrease of RS, indicating the presence of charge carriers in the NWs. According to the extracted values for RS and CS the NWs are classified into resistive and conductive. For conductive NWs charge transfer to a ferricyanide redox couple in the electrolyte is demonstrated and the ensemble average of the flatband voltage was determined. Variation of the lateral surface potential due to application of an external bias via the electrolyte is demonstrated. (paper)