Mechanisms of conductivity and energy spectrum of near-edge holes in Cu2ZnSnS4 powder samples

The resistivity, ρ(T), of Cu2ZnSnS4 powder samples, obtained by a solid-state reaction method from pure elements, exhibits an activated character. The Mott variable-range hopping charge transfer is observed between T ∼100-230 K, followed by the conductivity due to activation of holes into the states above the mobility threshold when T is increased. Such behavior, accompanied by semi-width W of the acceptor band, exceeding the mean acceptor energy, indicates overlap of the acceptor band states with those of the valence band, forming a joint near-edge hole spectrum in conditions of the strong degree of the compensation. The details of this spectrum have been determined, including positions of the Fermi level, μ, and the mobility threshold, as well as the density of the localized states at the Fermi level, g (μ). The acceptor concentration and the hole localization radius have been obtained, too. These parameters indicate the material to lie relatively far from the metal-insulator transition.