Energy spectrum of near-edge holes and conduction mechanisms in Cu2ZnSiSe4 single crystals

Abstract

Abstract A model of the energy spectrum of holes near the edge of the valence band of Cu2ZnSiSe4 is proposed from investigations of the resistivity, ρ(T), in Cu2ZnSiSe4 single crystals. The Mott variable-range hopping (VRH) conductivity mechanism is established in the temperature interval of ∼100–200 K, whereas between ∼200 and 300 K, the conductivity is determined by thermal excitations of holes to the mobility edge of the joint energy spectrum of the overlapped acceptor and valence bands. Parameters of the localized holes and details of the density of states near the edge of the valence band are determined, including the relative acceptor concentration, N/Nc ≈ 0.41–0.49 (where Nc ≈ 7 × 1018 cm−3 is the critical concentration of the metal–insulator transition), the relative localization radius a/aB ≈ 1.7–2.1 (where aB ≈ 13.1 A is the Bohr radius), the semi-width of the acceptor band, W ≈ 95–106 meV, centered at the energy E0 ≈ 59 meV above the top of the valence band, the average density of the localized states (DOS), gav ∼ (1.4–1.8) × 1016 meV−1 cm−3 and the DOS at the Fermi level, g(μ) ≈ (4.1–5.4) × 1015 meV−1 cm−3.