Band gap engineering of ZnO substituted with nitrogen and fluorine, ZnO1−3xN2xFx: a hybrid density functional study

Abstract

A series of first principles calculations within density functional theory (DFT) have been performed for ZnO, co-doped with N and F with the aim of engineering the band gap and improving its application to photo-absorption activity. A reliable hybrid functional of Heyd, Scuseria and Ernzerhof (HSE) has been used in order to predict the properties of ZnO_1−3xN_2xF_x. We describe a site disordered solid based on the consideration of configurational ensembles and statistical mechanics. The co-doped ZnO energy band gap shrinks and hence the photo absorption activity is enhanced by a considerable amount. The valence band maxima (VBM) of ZnO is dominated by O-2p orbitals with a considerable contribution from Zn-3d states. In co-doped ZnO_1−3xN_2xF_x just above the VBM a new band appears which is mainly composed of N-2p orbitals. The calculated formation energy ΔH_f for ZnO, in zinc rich and oxygen rich conditions are in good agreement with previous results. The calculated binding energies suggest that the stability of ZnO_1−3xN_2xF_x deteriorates at very dilute concentrations suggesting the use of heavy doping is desirable. Our results are helpful in understanding the growth conditions, electronic and optical properties of co-doped ZnO.