Surface phase matched templates for GaN hetroepitaxial growth*

Surface structural modifications are performed on Si(111)-7x7 surface, to find the appropriate template for high quality GaN growth. Adsorption of Ga forms stable superstructural phases of (1x1), (6.3x6.3) and (rt3xrt3) at 1.5ML, 0.8ML and 0.33ML respectively on a (7x7) reconstructed Si(111) surface. Using PA-MBE system, GaN of 0.75microns is grown at a relatively low temperature of 450oC on each of these phases. The films formed grow in the wurtzite phase with c-axis perpendicular to the Si(111) substrate surface. Now XRD, PL, XPS, AFM, FESEM and RHEED are employed to evaluate the structural, optical, compositional and morphological aspects of the GaN films. It is clearly observed that the 0.33ML (rt3xrt3) Ga phase results in the best quality GaN films, followed by the (6.3x6.3) phase and then the (1x1) phase. The (rt3xrt3) unit cell dimension matches with 2xa of GaN unit cell size, and thus GaN grows epitaxially on this surface with oriented single crystal grains. Thus, the results clearly demonstrate the possibility of employing low coverage metal induced surface phases as templates to form matched GaN films of high structural {\&} optical quality.