Single crystalline InxGa1-xN layers on germanium by molecular beam epitaxy

InxGa1-xN (InGaN) alloys are predominantly grown by heteroepitaxy on foreign substrates. Most often Al2O3, SiC and Si are used as substrates, however this complicates vertical conduction from the InGaN surface to the substrate backside. Therefore we investigate the heteroepitaxial growth of InGaN layers on Ge substrates. Single crystalline InGaN was obtained and domain formation was suppressed by using a thin GaN buffer layer. The InGaN shows compressive strain, which follows from the lattice mismatch with the GaN buffer layer. The In distribution is uniform throughout the InGaN layer, with no significant In segregation within the layer. Only at the surface, in a very thin layer of 20 nm, strong In segregation is observed with about 50% In. InGaN/GaN/Ge diodes show vertical current conduction of 1 A cm(-2) at -2 V. InGaN grown on Ge is therefore promising for device applications with preferred vertical conduction.