Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si 3 N 4 (Si 4+ ) but also in the intermediate nitridation states with one (Si 1+ ) or three (Si 3+ ) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si 1+ , Si 3+ , and Si 4+ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si 4+ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si 3 N 4 by molecular beam epitaxy (MBE). © 2010 Elsevier B.V. All rights reserved.