Investigation of three-step epilayer growth approach of GaN thin films to minimize compensation

In this paper, semiconductor nitride deposition are performed on sapphire substrates that have significant lattice mismatch such that strain accommodating nucleation layers are required to obtain reasonable crystallinity. The ultimate microstructure and electrical quality are of the subsequent film then becomes reliant on two things: the properities of the nucleation layer and heteroepitaxial nucleation on this nucleation layer. This is because the extended defects resulting in the film influence the level of compensation in the film. Thin film growth by MOCVD 1) AlN nucleation layer growth, 2) GaN nucleation and coalescence, and 3) GaN homoepitaxial growth on the fully coalesced film from step 2.GaN layer as determined by in-situ laser interferometry and confirmed by ex-situ AFM measurements. Select films are further characterised by cross-section TEM in an effort to correlate electrical property measurements with film defect and microstructure.