First-principles calculation of defect energies in zinc oxide and related materials.

摘要

First-principles calculation methods can predict and explain the electronic and many other properties of a wide variety of materials. In this dissertation, we use density functional theory to study electronic properties and defect energies in ZnO and ZnxMg1- xO. We use density functional perturbation theory to study the elastic constants, the piezoelectric constants, the static and high-frequency dielectric constants, and the zone-center vibrational modes in LiGaO 2 in comparison with ZnO and GaN.;The dissertation consists of three main parts. In the first part, we review the major concepts of the computational methods used in this work. Then we summarize the role of defects and impurities used for doping ZnO. In the second part, recent results concerning the structure and phase stability of ZnxMg1-xO alloy are discussed. An analysis of oxygen vacancy in ZnxMg 1-xO reveals a remarkable result: the oxygen vacancy prefers to be surrounded by Zn rather than Mg nearest neighbors. This feature is clearly supported by considering the statistical probability as well as the energetics of this defect. Because of the controversies in the literature regarding the oxygen vacancy in ZnO, the latter was selected for a further in-depth study of the defect level position. To accomplish this, we refined the previous application of the LDA+U model and revisited the treatment of the supercell finite size artifact. Good agreement is obtained with recent hybrid functional calculations on the position of the epsilon(0/2+) transition state. We also applied the same LDA+ U model to the Zn vacancy in ZnO and found that it correctly describes the localization for this self-trapped polaronic defect while LDA fails to do so. In the third part, we have studied the lattice-dynamical properties of LiGaO2, a material closely related to ZnO. The quantities calculated are the elastic constants, the piezoelectric constants, the static and high-frequency dielectric constants, and the zone-center vibrational modes. The nature of the vibrational modes is examined in terms of the mode eigenvectors. These are all compared to available experimental data in the literature. Satisfactory agreement is found when carefully examining the validity of the data in the literature. We also studied the electronic band structure of LiGaO2 using the quansiparticle self consistent GW approach and made an initial study of some of the point defect n-type and p-type doping candidates.