ON THE NEGATIVE MAGNETORESISTANCE IN THE VARIABLE-RANGE-HOPPING REGIME IN N-TYPE CUINSE2

Electrical conduction by the variable range hopping mechanism of Mott type with rho = rho0 exp (T0/T)s is observed in n-type CuInSe2 samples. As reported for p-type CuInSe2, two temperature regions having the same s almost-equal-to 0.25 but different rho0 and T0, are found. However, the physical explanations proposed for this behaviour in p-type material do not seem to be applicable in the present case. The field dependence of the magnetoresistance up to 8 T between 2 and 60 K is analyzed. A new empirical relation for the negative component of the form a e(-alphaTBc) where a, alpha, and c are constants, combined with the expression for the positive component proposed by Shklovskii explains very well the field dependence of the magnetoresistance.