Metal-insulator transition in manganese-doped InSb crystals

Abstract

Transport properties of manganese-doped InSb crystals with hole concentration close to the critical concentration Ncr of the metal-insulator transition (MIT) in p-InSb(Mn) was found to be different from MIT in semiconductors doped with non-magnetic impurities such as p-Ge(Ga), p-Si(P) and p-InSb(Ge). On the insulator side of the transition (NMn ≤ Ncr = 2 × 1017 cm-3) in the range of hole concentration p = 1-2 × 1017 cm-3 an activation type of conductivity with energy gap Δ = 7 × 10 -6 - 10-3 eV was observed. Thus, the usually observed variable range hopping conductivity in crystal semiconductors doped with non-magnetic impurities at low and super-low temperatures was not revealed in p-InSb(Mn) at p ≤ Ncr. An external magnetic field decreased Δ and caused a giant decrease of specific resistivity (ρ0/ ρB ∼ 104 at T ≤ 0.3 K and B ≥ 3 T). On cooling to temperatures below T = 1.5 K the Hall constant changed sign at B < 3 T. The change of Hall constant sign with decrease of temperature means that conductivity of p-InSb(Mn) and crystals compensated with Te - p-InSb(Mn, Te) - at low temperatures was caused by electrons. The proposed model associated an activation energy Δ at p ∼ Ncr with the energy gap between sub-bands formed in the impurity band. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.