The growth behavior of GaN film on Si(111) substrate by an ion-beam assisted evaporation process

Abstract

Highly oriented GaN thin films were grown on Si(111) substrate using an ion beam assisted evaporation method. Nitrogen ions, with a kinetic energy of about 40 eV, was supplied by a Kaufman ion source; and Ca vapor was supplied by thermal evaporation. The surface morphology of the nucleation layer, and the crystalline properties of 200-300 nm thick GaN epi-layer were investigated by atomic force microscopy, transmission electron microscopy, and X-ray diffraction. Film grown under a Ga-rich Aux condition produced film growth behavior of large islands of hexagonal configuration. Crystallinity on such film, however, was of poorer quality than other films with smaller islands, grown under high nitrogen ion Aux conditions. The full width at half-maximum of (0002) diffraction peak was measured at 52 arcminutes for the GaN epilayer single-stepwise grown at 660 degrees C. Ion-enhanced decomposition occurred, causing no film formation at substrate temperatures above 710 degrees C. Additionally, the effect of predeposition of a buffer layer on GaN crystallinity was investigated for surface roughness. AFM measurement revealed that the GaN buffer layer grown on Si(111) showed smooth surface under the relatively N-2(+)-sufficient condition. The introduction of thin GaN buffer layer, grown at 600 degrees C under N-2(+)-sufficient condition, worked on reducing the lattice-mismatch stress and in-plane misorientation of grains, and thus enhancing the crystallinity of the two-stepwise grown GaN epi-layer. Characteristic behavior of GaN epi-layers, single or two stepwise grown on Si(111), show a type of granular (columnar) epitaxy. (C) 1999 Elsevier Science S.A. All rights reserved.