NMR investigation of the diffusion and conduction properties of the semiconductor tellurium. I. Electronic properties

Abstract

The Knight shift and spin-lattice relaxation time of ${}_{}{}^{125}{}_{}{}^{}\mathrm{Te}$ in tellurium single crystals have been measured between room temperature and the melting point (724 K) using pulsed-NMR methods. Over the entire temperature range, the temperature dependence of the Knight shift is found to be determined completely by the intrinsic conductivity associated with thermally created conduction electrons in the conduction band, and the band-gap energy is determined. The spin-lattice relaxation time shows different temperature variations in two different regions: below 420 K ("low-temperature region"), spin-lattice relaxation is due to the conduction electrons (thus yielding information on the gap energy), while above 420 K ("high-temperature region") the relaxation process is due to the self-diffusion of Te atoms. Our Knight-shift results are found to agree quantitatively with a modified Knight-Korringa relation valid for semiconductors, which was originally derived by Bloembergen and which is reconsidered in the theoretical part of this article. The electronic contribution to spin-lattice relaxation is analyzed in terms of Hebel and Slichter's single spin-temperature theory as applied to semiconductors. The same gap energy, $E_g=0.30\mathrm{}$ eV, is found from both our Knight-shift and spin-lattice relaxation data. The self-diffusion properties of tellurium as extracted from our high-temperature relaxation studies will be the subject of a subsequent article.