Semiconducting properties of pure and Mn-doped chromium disilicides

Abstract

The phase analysis was carried out for the system ( l− x) CrSi 2 + xMnSi 2 in the range 0⩽ x⩽0.5 by X-ray technique. The solid solution Cr 1− x Mn x Si 2 was identified in the composition range 0⩽ x⩽0.225, where the added Mn-atoms occupied substitutionally the Cr-atom sites in the CrSi 2 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 CrSi 2 ( x = 0) was a p-type degenerate semiconductor, whose hole concentration was determined to be 7.7 × 10 20 cm −3 at room temperature. Mn-atoms introduced in the CrSi 2 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 Cr 1− x Mn x Si y . 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 × 10 35T 35 exp (− 3480 T ) , and the hole mobility as μ p = 7.0 × 10 4T − 3 2 in the acoustic scattering region. The effective mass of hole was found out to be 3.2 m 0 and independent of x, whereas that of electron varied from 20.2 m 0 for x = 0 to 7.5 m 0 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.