Variation of photoluminescence with carrier concentration in GaN

Abstract

Photoluminescence measurements are reported on undoped and on Ge doped single crystal epitaxial layers of GaN, having room temperature carrier concentrations (electrons) in the ranges 1.8 × 10 19 to 6.3 × 10 19cm −3 and 2.8 × 10 18 to 1.5 × 10 19cm −3 respectively. Both the previously reported donor-acceptor pair emission and a higher energy emission were observed in all samples. The intensity of the former greatly exceeded that of the latter in the undoped crystals of lower carrier concentration as it did in the Ge-doped crystals. The high energy luminescence peak was found to shift from 3.45 eV to 3.53 eV (77°K) according to increasing carrier concentration. This was found to be consistent with a model of band to band recombination across a band gap of 3.50 eV (1.6°K) for crystals with carrier concentrations in the range n > ∼ 5 × 10 18 cm -3, a Burstein shift mechanism being responsible for the observed shift of the luminescence peak.