Photoreflectance study on the surface states of n-type GaN

Photoreflectance spectroscopy was used to study n-type GaN epilayers with d oping concentrations ranging from 3 x 10(17) cm(-3) to 5 x 10(18) cm(-3). T he relative change of reflectance signal \Delta R/R\ was investigated as a function of doping concentration ND. The value of log(10)(\Delta R/R\) was found to be proportional to log,,,(ND) with a slope of -1.2 +/- 0.2. This r esult can be explained by a simple model based on an assumption that low-de nsity surface states exist in the surface of GaN. The result may clarify ce rtain issues in the existing Schottky barrier experiments.