Optical and structural characterization of N-face GaN epilayers grown on Ge (111) by plasma assisted molecular beam epitaxy

Abstract

The luminescence properties of N-face GaN, heteroepitaxially grown on Ge, is investigated and correlated with surface morphology and strain. The GaN surface shows a dense array of deep faceted pits at the end of threading dislocations. The density of defects increases with the epilayer thickness and relaxes the strain. GaN-on-Ge shows broad and intense photoluminescence, which exceeds the intensity of GaN grown on silicon, sapphire and SiC. Cathodoluminescence reveals the correlation of luminescence features with different crystal facets. Combined with the presence of impurity-induced band-tail states this leads to broad (330-410 nm) and intense optical spectra for N-face GaN-on-Ge.