Development of Homoepitaxially Grown GaN Thin Film Layers on Freestanding Bulk m-plane Substrates by Metalorganic Chemical Vapor Deposition (MOCVD)

Abstract

AbstractHigh quality homoepitaxial growth of m-plane GaN films on freestanding m-plane HVPE GaN substrates has been performed using metalorganic chemical vapor deposition. For this a large growth space was studied. Large areas of no-nucleation along with presence of high density of defects were observed when layers were grown under growth conditions for c-plane GaN. It is believed that these structural defects were in large part due to the low lateral growth rates as well as unequal lateral growth rates in a- and c- crystallographic directions. To achieve high quality, fully coalesced epitaxial layers, growth conditions were optimized with respect to growth temperature, V/III ratios and reactor pressure. Higher growth temperatures led to smoother surfaces due to increased surface diffusion of adatoms. Overall, growth at higher temperature and lower V/III ratio decreased the surface roughness and resulted in better optical properties as observed by photoluminescence. Although optimization resulted in highly smooth layers, some macroscopic defects were still observed on the epi-surface as a result of contamination and subsurface damage remaining on bulk substrates possibly due to polishing. Addition of a step involving annealing of the bulk substrate under H2: N2 environment, prior to growth, drastically reduced such macroscopic defects.