HOMOEPITAXIAL GROWTH OF GAN UNDER GA-STABLE AND N-STABLE CONDITIONS BY PLASMA-ASSISTED MOLECULAR-BEAM EPITAXY

The structure, morphology, and optical properties of homoepitaxial GaN layers grown by molecular beam epitaxy on metalorganic chemical vapor deposition (MOCVD)-grown GaN ''template'' layers were investigated as a function of the group III/group V flux ratio during growth. GaN lay ers grown with a low III/V ratio (N-stable growth) displayed a faceted surface morphology and a tilted columnar structure with a high densit y of stacking faults. In contrast, films grown with a high III/V ratio (Ga-stable growth) displayed comparable structure to the underlying M OCVD-grown template. The transition from N-stable to Ga-stable growth modes was found to occur over a narrow range of Ga fluxes at a growth temperature of 650 degrees C. Evidence of Ga accumulation and step-flo w growth was observed for films grown under Ga-stable conditions, lead ing to the formation of spiral growth features at the surface terminat ion of mixed edge/screw dislocations. Photoluminescence measurements i ndicate that the deep-level (similar to 550nm) emission is increased r elative to the near-band edge emission for films grown under N-stable conditions. (C) 1997 American Institute of Physics.