DFT study of halogen impurity in diamond

A first-principles study has been carried out to evaluate the electronic properties of diamond doped with halogen X (= F, Cl, Br, I) based on density functional theory (DFT). Our work shows that doping becomes more difficult in the order F < Cl < Br < I for either substitutional or interstitial doping into diamond. Substitutional doping is energetically more favourable owing to smaller formation energy than the interstitial doping. The calculated results show that the F defect accepts electrons and acts as acceptor in diamond. However, the dopant Cl/Br/I donates electrons to diamond lattice, which indicates that Cl/Br/I may serve as a donor in diamond. It is found that substitutional I is a good choice for achieving n-type diamond material among the donors. Further calculations examine the influence of H atom on the electronic properties of diamond doped with donor dopant Cl/Br/I and show that H atom incorporation makes Fermi level E-F shift towards the valence band (VB) and the activation energy of the donor Cl/Br/I increases. Therefore, halogen impurities doping into diamond should be carried out under H-poor environments. In addition, X-s (X = Cl, Br, I) prefers to bind to vacancy defects to form a X-s-V complex, which is no longer a shallow donor.