Effect of Interstitial Si on Different Boron Nitride Allotropes

Abstract

Boron nitride (BN) is a very interesting material, being isoelectronic with diamond. It can form the following allotropes; hexagonal (h-BN), cubic (c-BN), wurtzitic (w-BN), and rhombohedral (r-BN). However, there are severe problems with the syntheses of some of these crystalline phases, especially using chemical vapor deposition (CVD) techniques. The underlying reasons for these growth difficulties are of largest importance to investigate more in detail. For each of these crystalline phases, the thin film surface reactivity is one factor that has a major influence on both growth and surface properties. The surface reactivity of specifically the B and N surface sites on these crystalline phases has therefore here been studied by performing first-principle density functional theory (DFT) calculations under periodic conditions. The following surfaces were studied: c-BN (100), h-BN (001), w-BN (100), and r-BN (001). The adsorption energy for different surface-terminating species (H, F, and Cl) has been taken as a measure of surface site reactivity. Since experimental studies have shown that Si contamination will improve the possibility for growth of r-BN, the effect of this dopant has also been considered in the present work. The results indicate that the surface reactivities for nonterminated N-sites are more pronounced for the situations with an otherwise completely covered surface by H species (compared to F and Cl). In fact, this was the situation for all BN allotropes (c-, h-, w-, and r-BN). The surface reactivities for nonterminated B-sites showed the same behavior for the w- and r-BN phases. For the c- and h-BN surfaces, a nonterminated B surface site on an otherwise H-terminated surface is, however, slightly less reactive compared to the corresponding F-terminated surface. In addition, there were extreme problems to terminate the various surfaces with Cl species. Furthermore, the existence of interstitial Si dopants did only show a positive effect for the reactivity of a bare B-site on the h- vs r-BN surface (on an otherwise H-terminated surface). However, the calculated stabilization energy showed that it is not possible to Si dope the h-BN surface lattice. Hence, it was only for r-BN that interstitial positioning of Si was found possible, and that also gave a positive effect on the surface reactivity.