Electronic structure and optical transition in heavy metal doped ZnO by first-principle calculations

We present the electronic states and enhancement features of optical transition in heavy metal doped ZnO, and reveal the intrinsic electronic structure by using an ab initio pseudopotential method based on density functional calculations. Structural calculations show that the Ag- and Au-doped ZnO crystals have lattice distortion of 0.09-0.1 angstrom for a and 0.13-0.15 angstrom for c, respectively. Band structure calculations reveal that the energy levels of Ag- and Au-doped ZnO are above the VBM of pure ZnO 0.12 eV and 0.4 eV, respectively. Ag 4d and Au 5d states have shallow energy level located near the valence band, and can enhance the electronic states of valence band. Furthermore, the results of imaginary part of dielectric function epsilon(2)(omega) indicate that the Ag- and Au-doped ZnO can induce enhancement of UV band-edge transition which is due to the Ag 4d (Au 5d) states-Zn 4s states transition. The optical transition of Ag-doped ZnO is concentration-dependent and Ag 4d states suffer the transformation from the discrete energy states to localized states. Besides, the role of shallow Zn 3d and Ag 4d electrons is critically examined, and the available experimental data are used to compare with the calculated results. (C) 2011 Elsevier B.V. All rights reserved.