First principles calculations on ZnO non-equilibrium phase

In this thesis work, the electronic and optical properties for the non-equilibrium boron-nitride phase of ZnO have been studied. To understand the difference between the BN phase and the equilibrium WZ phase, first principles approaches such as DFT, hybrid functional and the GW approximation have been studied and applied. The lattice constant has been obtained by performing full relaxation within the DFT approximation. With the DFT optimized structure, we calculated the band structures and band gaps for both phases. We have found an about 0.2 eV larger band gap for BN phase with all methods. A discrepancy between the lattice constant obtained from experiment and that from simulation has also been investigated. We calculated the band structure for both the experimental lattice and the computed lattice obtained from relaxation. We have found an inconsistency between the experimental lattice constant and the experimental band gap. Further, by solving the Bethe-Salpeter Equation, excitonic effect has been included and the exact optical spectrum for both structure has been obtained. We have found a large optical anisotropy for BN structure. Lastly we calculated the exciton binding energy for the BN phase and have found a larger excitonic effect in this phase