We present our preliminary results of a systematic theoretical study of the adsorption of N and Ga over boron phosphide (BP) (1 0 0) (2 x 1) surfaces. We have analyzed the changes in the bond lengths and bond angles before and after deposition. Based on our obtained results, we show that the N atom prefers to make bonds with the surface dimers, during the nitridation of the BP surfaces, which favors the growth of cubic GaN thin films. Over the B-terminated surfaces, the Ga atoms prefer to make bridges between two B-dimers, and the final structure of the GaN films tends to be hexagonal. At P-terminated surfaces, there is a competition between the Ga adsorption over the surface dimers, and over the empty sites of the surface. While the latter favors the formation of surface Ga droplets over this surface, the adsorption over the P-dimers can result in cubic GaN samples. (c) 2008 Elsevier B.V. All rights reserved.