Improved surface morphology in GaN homoepitaxy by NH3-source molecular-beam epitaxy

GaN homoepitaxial layers of improved surface morphology were obtained by a NH3-source molecular-beam epitaxy method supplying a proper reactive NH3-to-Ga flux ratio (V/III ratio) on the growing surface, combined with a procedure to prevent the surface roughening of the GaN/ (0001) Al2O3 epitaxial templates, which were prepared by metalorganic vapor-phase epitaxy. In situ monitoring on the heated templates revealed their thermal decomposition above,700degreesC in ultrahigh vacuum, which gave rise to surface unevenness of both initially atomically flat templates and the homoepitaxial layers. The surface flatness was maintained by depositing the "flux-modulated" GaN prior to the high-temperature growth, where Ga flux was supplied intermittently during heating the template under continuous NH3 flow. The increase in V/III ratio greatly improved the surface flatness. As a result of the epilayer/template interface control and growth optimization, the epilayers exhibited higher mobility, smaller full width at half-maximum value (34 meV) of excitonic photoluminescence (PL) peak, and longer PL lifetime of 180 ps at 293 K. (C) 2004 American Vacuum Society.