Single-crystalline GaN films were grown on Si(111) substrates by metal organic chemical vapor deposition (MOCVD) using a silicon nitride (SiNx) buffer achieved through the nitridation of substrate. The effect of in situ substrate nitridation on the GaN crystalline quality was investigated with the nitridation being performed at 750, 950 and 1120 degrees C, respectively. It demonstrates that the nitridation temperature greatly influences the surface morphology and PL spectra of GaN grown atop SiNx buffer. The surface roughness of GaN film grown atop the Si substrate nitridated at 950 degrees C exhibited a root mean square (RMS) value of 5.057 nm for surface roughness evaluated by atomic force microscopy (AFM). Additionally, a strong photoluminescence (PL) emission at 365 run (3.4 eV) with the full-width at half-maximum (FWHM) of 61.1 meV was achieved at room temperature. Particularly, a yellow luminescent band that was observed when the nitridation was performed at 750 degrees C was greatly reduced to a degree that could hardly be recognized. Alternatively, nitridating the substrate at 1120 degrees C resulted in a strong but much wider PL spectrum. Accordingly, an effective buffer of SiNx for the growth of GaN on Si substrates can be formed by introducing the substrate nitridation at a due temperature around 950 degrees C before the commencement of epitaxial growth. (c) 2005 Elsevier B.V. All rights reserved.