Semiconducting properties of pure and Mn-doped chromium disilicides

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Abstract

The phase analysis was carried out for the system (lx) CrSi2 + xMnSi2 in the range 0⩽x⩽0.5 by X-ray technique. The solid solution Cr1−xMnxSi2 was identified in the composition range 0⩽x⩽0.225, where the added Mn-atoms occupied substitutionally the Cr-atom sites in the CrSi2 structure. Resistivity, Hall coefficient as well as thermoelectric power were measured as functions of temperature in the range, 80–1200 K and composition x in the single phase region, 0 ⩽x⩽0.225. The pure CrSi2 (x = 0) was a p-type degenerate semiconductor, whose hole concentration was determined to be 7.7 × 1020 cm−3 at room temperature. Mn-atoms introduced in the CrSi2 crystal were found to act as donors. The forbidden energy gap was determined to be 0.30 eV from the Hall-data in the intrinsic region. With increasing x, a conversion from p- into n-type semiconductor took place in Cr1−xMnxSiy. From the analysis of Hall- as well as resistivity-data, the mobility ratio b was obtained as a function of composition x. It was revealed that b increased with increasing x from 0.01 for x = 0 to 0.12 for x = 0.182. The electron-hole concentration product could be expressed as np = 1.2 × 1035T35exp (−3480T), and the hole mobility as μp = 7.0 × 104T32 in the acoustic scattering region. The effective mass of hole was found out to be 3.2 m0 and independent of x, whereas that of electron varied from 20.2 m0 for x = 0 to 7.5 m0 for x = 0.182. When these parameters are used, the theoretical temperature variation of the thermoelectric power curve was found out to be in good agreement with the measurement.

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