Electronic properties of zno doped with transition metals

Transparent conduction oxides are potential materials that can be used in invisible electronics circuits, solar cells and large area displays. ZnO, a transparent material in the visible range of the spectrum whose band gap can be engineered by doping, falls in this category and is studied intensively in recent years from different perspectives.Moreover, since the magnetic properties of ZnO can be modified by doping, it attracts a great deal of interest for spin polarized current production and for applications in spintronics. In this study, the variation of band gap, lattice constants and the effective mass of electrons and holes in doped ZnO with transition metals (Cu, Fe, Ni, Co, Mn) are studied. Doping ratios (1\%-10\%) are kept at low values just like in experiments. The variations in the band gap are determined by ABINIT package (an open source code program) which uses Density Functional Theory in the frame work of Local Density Approximation. It is known that Density Functional Theory is not capable of predicting the band gaps correctly and its reasons are well known. Since the purpose here is to determine the direction of variation of band gap, we have concentrated on the variation of band gap by doping rather than on its absolute value. When doped with the transition metals mentioned above, it is observed that the band gap is decreased with the increase of doping ratio. Using the band structure, the effective masses of both electrons and holes are calculated. These are calculated along specific directions in the reciprocal lattice. It is observed that the effective masses also changes with doping ratio and with the material used for doping. When doped with transition metals, the lattice constant a increased (except for Ni) and lattice constant c increased and/or decreased depending on the ratio of doping and the material used in doping.