First principles study and variable range hopping conductivity in disordered Al/Ti/Mn-doped ZnO

Abstract

Based on first principles electronic structure calculations using the Coherent Potential Approximation (CPA) in the Blackman–Esterling–Berk (BEB) multiscattering formalism and the variable range hopping (VRH) model proposed by Mott, we evaluate the low temperature dc conductivity and its temperature dependence for n-doped wurtzite-type M:ZnO, with M = Al, Ti, Mn, at concentrations of 2, 5 and 10 at.% respectively. We theoretically determine the phenomenologic quantities in the expression of the hopping conductivity, as well as the temperature range in which the VRH model is applicable to the investigated compounds. We show that self-consistent CPA-BEB and LSDA+U calculations yield reasonable band gaps, dopant state localization and also spin magnetic moments for the Ti and Mn systems. These results are discussed in comparison with reported data obtained by supercell LSDA+U calculations for similar systems. The results in this study point to 2–5 at.% Ti and approximately 2 at.% Al codoping in wurtzite-type ZnO as an interesting option to obtain a material with an increased low temperature dc conductivity and ferromagnetic background.