Charge Transfer across the n-Type GaN-Electrolyte Interface

The interfacial charge transfer characteristics of n-type GaN are investigated in pure phosphate buffered saline, as well as in solutions containing I-/I-3(-) or hydroquinone/benzoquinone redox couples. Cyclic voltammetry and transient photoresponse measurements in the presence of above-bandgap illumination reveal that hole transfer to the solution is mediated by surface states in all cases. For measurements in pure PBS, a modification of the surface during cyclic potential sweeps is observed. In contrast, the presence of the redox species used in this work efficiently suppresses the oxygen evolution reaction and the associated surface modification. Furthermore, charge transfer to the redox couple is fully reversible using GaN as a dark cathode and photoanode, respectively. The presented study is of significant importance for applications of GaN in photocatalysis and biosensing, where the stability of (bio)functionalized surfaces is an essential requirement.