Electrical Conduction Mechanism of β-MnTe Thin Film with Wurtzite-Type Structure Using Radiofrequency Magnetron Sputtering

Manganese telluride (MnTe) compound is known to be a polymorphic chalcogenide. Recently, it has been reported that the MnTe shows nonvolatile memory properties with a significant change in resistance via a polymorphic transition between NiAs-type (NC) structure (low resistance) and wurtzite-type (WZ) structure (high resistance). This crystalline polymorphic MnTe is expected to realize a phase-change memory with fast operation speed and ultralow operation energy. While the NC-MnTe, generally designated as α-MnTe, is intensively studied, WZ-MnTe is still poorly understood. Herein this study, electrical conduction mechanism of a β-MnTe film with a WZ-type structure is studied. A resistivity, Hall mobility, and Seebeck coefficient of the WZ-MnTe film are measured at various temperatures. The temperature dependence of resistivity in the temperature range 120–300 K clearly indicates that the WZ-MnTe film shows a variable-range hopping (VRH) conduction. In this temperature region, with decreasing temperature, the conduction mechanism changes from Mott–VRH conduction to Efros–Shklovskii VRH conduction at about 210 K. Furthermore, the low thermally activated Hall mobility, occurrence of Hall-effect sign anomaly, and relatively low activation energy for thermopower, which are the observed results, suggest that the small polaron hopping conduction is dominant above 310 K.