Incorporation of germanium for n-type doping of cubic GaN: Incorporation of germanium for n-type doping of cubic GaN

We introduce germanium as an alternative to silicon for n-type doping of cubic gallium nitride. Layers with electron concentrations up to 3.7x10(20)cm(-3) were grown by plasma-assisted molecular beam epitaxy on 3C-SiC substrates. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements were performed to verify the incorporation of Ge into our layers. The incorporation of Ge is in good agreement with the trend of the Ge vapour pressure curve. For the highest doped sample a drop of the incorporation efficiency is observed. A reduction of the growth rate is noticed for high Ge fluxes. Additionally, a sample comprising an alternating pattern of Ge-doped and not intentionally doped interlayers was grown. In the recorded TOF-SIMS depth profile we observe that in doped regions the Ge concentration increases along the growth direction. A gradually decreasing amount of Ge is incorporated into each overlying not intentionally doped interlayer. We suppose these observations are due to segregation effects and a resulting accumulation of Ge at the sample surface during growth. (C) 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim