Very low dislocation density, resistive GaN films obtained using transition metal nitride interlayers
Moram, M A and Kappers, M J and Zhang, Y and Barber, Z H and Humphreys, C J
A threading dislocation density (TDD) reduction method for GaN films is described. Thin amorphous layers of Sc, Hf, Nb, Zr and Cr were deposited on MOVPE-grown GaN-on-sapphire templates with a TDD of 5 × 1\^09 cm–2 and 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 × 10\^9 cm\^–2. The NbN and ZrN layers formed oriented holey network structures. The Cr layer did not nitride. Coalesced GaN epilayers grown on the ScN layers had the lowest dislocation density of 3 × 1\^07 cm–2 (un-coalesced GaN on ScN had TDDs as low as 5 × 10\^6 cm\^–2). Unlike GaN films grown using multiple SiNx interlayers, which contain a similar proportion of edge and mixed dislocations, the GaN-on-ScN layers contain substantially fewer mixed than edge dislocations, a proportion similar to that of the high-TDD template. The low-TDD GaN epilayers grown on ScN are also highly electrically resistive.
Department of Materials
Imperial College London
Royal School of Mines
London, SW7 2AZ - UK