Carrier behavior in the vicinity of pit defects in GaN characterized by ultraviolet light-assisted Kelvin probe force microscopy

Surface potentials in the vicinity of V-pits (cone bottom) and U-pits (blunt bottom) on epitaxial GaN surface have been systematically studied using ultraviolet (UV) light-assisted Kelvin probe force microscopy (KPFM). The band structure models are established to understand variation of the surface potentials at the pits and planar surface with and without UV light. The photo-generated carrier behavior at the pit defects is studied. According to the surface potential results, it can be deduced that the carrier distributions around the V- and U-pits are uneven. In dark, the electron concentration at the bottom of V-pit (30n0) and Upit (15n0) are higher than that at planar surface (n0). Under UV light, for V-pit, the electron concentration at the cone bottom (4.93×1011n0) is lower than that at the surrounding planar surface (5.68×1013n0). For U-pit, the electron concentration at the blunt bottom is 1.35×1012n0, which is lower than that at the surrounding planar surface (6.13×1013n0). The non-equilibrium electron concentrations at different locations are calculated. Based on the non-equilibrium electron concentration, it can be concluded that the carrier recombination rate at pit defects is higher than that at planar surface.