NONOHMIC CONDUCTIVITY OF GESB NEAR A METAL-INSULATOR-TRANSITION

Electric fields up to 120 V/cm were used at temperature of 4.2-60 K to determine the electrical conductivity sigma and the Hall coefficient R of Ge:Sb crystals with electron densities n=1 X 10(17) cm-3 and 2 X 10(17) cm-3, which were close to the critical value n(c) corresponding to a metal-insulator transition (in the case of Ge:Sb this critical v alue was n(c) = 1.5 X 10(17) cm-3). The nonohmic conductivity observed at temperatures below the Hall coefficient maximum \R(T)\max could be explained, both for n < n(c) and n > n(c), by the ionization of elect rons from the impurity band to the conduction band. An analysis of the temperature and field dependences of R and sigma was used to find the temperature to which the electron gas was heated and the energy relax ation time.