Photoreflectance investigation of band gap renormalization and the Burstein-Moss effect in Si doped GaN grown by MOVPE

This work reports on the photoreflectance (PR) study of Si doped GaN layers (GaN:Si) with different doping levels (2.1×1017-2.8×1019 cm−3). GaN:Si samples have been successfully grown on sapphire substrate by metalorganic vapor phase epitaxy (MOVPE). Room temperature PR spectra showed Franz-Keldysh oscillation (FKO) features, reflecting the existence of a built-in electric field in the epilayers. The band gap energy determined using the FKO theory, is observed first to decrease and then to increase with increasing electron concentration. This result is explained by the competing effects of band gap renormalization and Burstein--Moss band filling. Based on theoretical approach and experimental results, the interplay between these phenomena is systematically studied.