Role of the surface density of states in understanding size-dependent surface band bending in GaN nanowires

Abstract

In semiconductor nanostructures, surface states play a very important role in determining the surface potential or contact potential difference (CPD). We measure the CPD value of individual GaN nanowires (NWs) using Kelvin probe force microscopy (KPFM). The corresponding surface band bending (SBB) is calculated from the measured CPD value and is found to increase with a decrease in the NW size. In order to investigate the size dependence of the SBB, the electronic density of states of the surface atoms of the nanowires at different values of the diameter are calculated using the first-principle density functional theory (DFT). The calculated density of states of the nanowires revealed size-dependent occupancy and shift of conduction band edge. The relative position of the conduction band edge corroborates with size-dependent SBB values obtained from KPFM measurements.