Spin-lattice relaxation times (T1) and Knight shifts were measured for Cd113 nuclei in 12 CdS crystals doped with various amounts of chlorine. Hall coefficients were measured in order to estimate conduction-electron concentrations. Data were obtained for all samples at 300 °K and for some highly doped samples at 77, 4.2, and 2.13 °K. Metallic properties were observed in all samples having electron concentrations n>2×1018 cm-3. At 300 °K, we find 1/T1∝n for nonmetallic samples and 1/T1∝n2/3 when samples are metallic. The latter proportionality continues to hold at lower temperatures. The dependence of T1 on n becomes increasingly less pronounced at lower temperatures in the nonmetallic samples indicating that the nuclear relaxation becomes at least partially dependent on mechanisms other than conduction electrons, such as spin-diffusion coupling to paramagnetic impurity sites. In the metallic samples, the Knight shift K∝n1/3 and the Korringa product is a constant: T1TK2=3.3×10-6 sec °K. Both the Knight shift and Korringa product decrease sharply for n<2×1018 cm-3. Our analysis shows that the Mott transition (formation of an impurity conduction band or transition to "free" conduction) occurs in a region 5×101718 cm-3 and that the impurity conduction band and the CdS conduction band become merged (i.e., the Fermi level crosses into the CdS conduction band) in a region 1.6×101818 cm-3.
Adams, F. D.,
Look, D. C.,
Brown, C. L.,
& Locker, D. R.
(1971). Nuclear-Magnetic-Resonance Studies of the Semiconductor-to-Metal Transition in Chlorine-Doped Cadmium Sulfide. Physical Review B, 4 (7), 2115-2123.