First-principles analysis of Cx(BN)1-x ordered alloy

We present full potential linearized augmented plane wave calculations for the ordered alloy C-x(BN)(1-x). The generalized gradient approximation is used for the exchange-correlation potential. The ground state properties are determined for the bulk materials (C and BN) as well as for the average concentration (x = 0.5) of the alloy. Results have been compared to available experimental and theoretical works with favorable agreement. To model the alloy, we have followed the method developed by Zunger and co-workers [ 1, 2] where the alloy is studied in an ordered structure designed to reproduce the most important pair correlation functions of a random alloy and where the chemical and structural effects are well described. Detailed analysis is given especially for the band-gap bowing. The main contribution to the disorder is due to the chemical effect, while structural and relaxation contributions are negligible. This should be expected since there is a weak lattice mismatch between C and BN and a strong mixed ionic and covalent bonding between the elemental (C) and the III-V compound (BN) which form the alloy. The global bowing compares well with those from previous virtual crystal approximation studies. Results also show the importance of the total bowing for the direct band gap. (C) 2003 Elsevier Science Ltd. All rights reserved.