A threading dislocation density reduction method for GaN films was described. Thin amorphous layers of Sc, Hf, Nb, Zr and Cr were deposited onto MOVPE-grown GaN-on-sapphire templates with a threading dislocation density of 5 x 109/cm2; annealed in NH3 to form metal nitrides. The ScN layer remained continuous, with a very low pinhole density, while the HfN layer contained a high pinhole density of approximately 3 x 109/cm2. The NbN and ZrN layers formed oriented holed network structures. The Cr layer did not undergo nitridation. Coalesced GaN epilayers grown onto the ScN layers had the lowest dislocation density of 3 x 107/cm2 (un-coalesced GaN on ScN had threading dislocation densities as low as 5 x 106/cm2). Unlike GaN films grown using multiple SiNx interlayers, which contained a similar proportion of edge and mixed dislocations, the GaN-on-ScN layers contained substantially fewer mixed than edge dislocations; a proportion similar to that of the high threading dislocation density template. The low threading dislocation density GaN epilayers grown onto ScN were also highly electrically resistive.

Very Low Dislocation Density, Resistive GaN Films Obtained using Transition Metal Nitride Interlayers. M.A.Moram, M.J.Kappers, Y.Zhang, Z.H.Barber, C.J.Humphreys: Physica Status Solidi A, 2008, 205[5], 1064-6