Infrared reflectance investigation of undoped and Si-doped GaN films on sapphire

Abstract

Undoped and Si-doped GaN films grown on sapphire were investigated by infrared reflectance spectroscopy. The carrier concentrations were determined from theoretical simulation fitting to the reststrahlen band, which are in agreement with Hall measurements. A damping behavior of the interference fringe contrast was observed, which can be well explained by the effect of an interface layer. Such interface layer was proposed to be due to the high density of defects near the GaN-substrate interface. As the doping level increases, this contrast damping is weakened, accompanying with the lowering of reflectivity in the higher frequency region. Combined with the atomic force microscopy analysis, an improvement of the interface quality, due to the Si-doping, is demonstrated.