Study of Semiconductor-to-Metal Transition in Mn-Doped FeSi2

The electrical resistivity, the thermoelectric power, and the Hall coefficient for Fe${\mathrm{Si}}_2$ doped with Mn or Co have been measured over the temperature range 300-1400 K. The energy gaps deduced from the slopes of curves of the resistivity versus reciprocal absolute temperature decrease with increasing Mn concentration. The resistivities and thermoelectric powers show a semiconductor-to-metal transition with hysteresis, and the transition temperature decreases with increasing Mn concentration. Specimens both doped with Mn and undoped are found to be $p$-type semiconductors in the temperature range below the transition temperature. The added Mn acts as an acceptor. The analysis of resistivity in the semiconducting state was based on a model predicting that the narrow band in the metallic state is split by the crystalline-structure distortion. The density of states for the undoped specimen is found to be 7.46×${10}^{22}$ ${\mathrm{cm}}^{-3\mathrm{}}$. Assuming that the value of the density of states is invariable in all specimens, the analyzed results are in reasonable agreement with the resistivities observed in the intrinsic region.