Semiconducting properties of nonstoichiometric manganese silicides

Abstract

Electrical resistivity, Hall coefficient and thermoelectric power were measured on manganese silicides of composition MnSi_2−x withx ranging from 0.25 to 0.28 in the temperature range from 80 to 1100K. At higher temperatures a forbidden energy gap estimated from the resistivity data was about 0.40 eV. It was confirmed that MnSi_2−x was a degenerated semiconductor and that the hole concentrations in the degenerated state varied from 1.8 to 2.3×10²¹ cm⁻³. The ratio of electron to hole mobility was less than unity. The intrinsic resistivity and the hole mobility varied with temperature as 3.6×10⁻⁴ exp(2320/T) and 1.2×10⁴ T ^−3/2 respectively. The value of Hall coefficient calculated by using a mobility ratio of 0.02 was in good agreement with that observed in the intrinsic region. From the relationship between hole concentration and thermoelectric power for MnSi_1.73 near room temperature, the hole effective mass was estimated to be twelve times as large as the free electron mass. The calculation of the thermoelectric power was carried out based on the assumptions that the scattering of carriers is dominated by acoustic lattice scattering and that the carriers obey Fermi-Dirac statistics. The calculated results were in reasonable agreement with the observed thermoelectric powers in the temperature range from 150 to 1100K.