Low-temperature impurity breakdown in Ni-doped CdGeAs2 amorphous films

Electric conductivity of Ni-doped CdGeAs2 amorphous films was studied in electric fields F<6x103 V/cm at 4.2-530 K. It is shown that dependences σ=σ(T,F) are related to the existence of impurity states zone of 0.1 eV width and located in the vicinity of the upper valence zone limit. In specimens containing 0.5 wt.%Ni, a low-temperature impurity breakdown is observed in the temperature range of 4.2-12 K (current increase by 3-4 orders for almost constant voltage on specimen). With T increase above 12 K the impurity breakdown is accompanied with switching effect, and voltampere characteristics (VAC) gain the type characteristic of conditions where appearance of negative differential resistance (NDR) results in current filament. Specimens VAC with a higher (2.0 wt.%) Ni concentration have only sections with NDR, no sections with vertical growth of current are observed