Evidence of neutral impurity scattering in mercury sulphide (α-HgS) in the temperature range 77–300 K correlation with chemical analysis

Abstract

Five natural or synthetic trigonal HgS single crystals have been studied by transport experiments in the temperature range 77–300 K. The classical d.c. technique has been used to measure the Hall coefficient and the resistivity. The temperature dependence of the free carrier density in the conduction band associated to a chemical analysis have brought to light the presence of neutral donor impurities with a density much larger than the ionized ones, which has led us to consider the existence of neutral impurity scattering even at room temperature. A detailed study of the mobility has shown that, among the four possible and efficient scattering processes, (neutral impurities, ionized impurities, acoustical phonons and optical polar modes), the most efficient in the whole experimental temperature range is the neutral impurities one. However, at room temperature, the polar optical mode becomes comparable to the previous one. The agreement obtained between the experimental values of the mobility and the calculated ones by taking into account these four scattering modes is very good in the whole temperature range. So for the first time an explanation is given for the rather low value of the mobility in mercury sulphide. This explanation of the mobility behaviour is in good agreement with the results of the chemical analysis which shows in HgS-α the presence of impurities very much larger than that of the ionized impurities one.