Films of Sc and Ti (5 and 20nm thick) were deposited on 500nm GaN/Al2O3 templates, then annealed in mixed NH3 and H2 at 1070C in an MOCVD reactor to produce ScN and TiN films. This resulted in a dense array of holes in the TiN layers, but had little effect on ScN layers. The dislocation densities in GaN grown on the masked templates were reduced significantly from 5.0 x 109/cm2 on the templates to 1.5 x 108/cm2 on the thin TiN layers and were reduced almost a 100-fold to 6.4 x 107/cm2 on the thin ScN layers, despite the absence of holes in the latter. TiN layers produced GaN films under compressive residual stress and ScN layers gave GaN films under tensile residual stress; the levels of stress varied with mask thickness. The masking layers therefore provide a convenient method to control both dislocation densities and wafer curvature, both of which were necessary for successful device fabrication.

Growth of Low Dislocation Density GaN using Transition Metal Nitride Masking Layers. M.A.Moram, M.J.Kappers, Z.H.Barber, C.J.Humphreys: Journal of Crystal Growth, 2007, 298, 268-71