Ge doping of GaN beyond the Mott transition

Abstract

We present a study of germanium as n-type dopant in wurtzite GaN films grown\nby plasma-assisted molecular beam epitaxy, reaching carrier concentrations of\nup to 6.7E20 cm-3 at 300K, well beyond the Mott density. The Ge concentration\nand free carrier density were found to scale linearly with the Ge flux in the\nstudied range. All the GaN:Ge layers present smooth surface morphology with\natomic terraces, without trace of pits or cracks, and the mosaicity of the\nsamples has no noticeable dependence on the Ge concentration. The variation of\nthe GaN:Ge band gap with the carrier concentration is consistent with\ntheoretical calculations of the band gap renormalization due to\nelectron-electron and electron-ion interaction, and Burstein-Moss effect.\n