Nonlinear percolation conductivity and negative differential resistivity in microcrystalline PbTe layers with an adjustable potential well

The effect of electric fields on the electrical conductivity of PbTe films with block sizes smaller than the Debye screening length is studied. As the temperature is varied, a readjustment of the potential well is observed due to thermal spread of barriers with height ϕkT and the expansion of higher barriers. Spatial ensembles, which consist of several blocks that increase rapidly with temperature, are established for each T. This process leads to an increase in the height of the potential barriers as the linear size of these ensembles increases. This determines the potential well in these films and their nonlinear properties, which originate in the nonlinear percolation conductivity of a microscopic crystalline system with intergranular barriers. A comparison with the experimental data of Shklovskii shows that the scale length of the spatial inhomogeneity a=3.7×10⁻⁶ cm at T=4.2 K corresponds to the average block size. The value of a increases with temperature, reaching 5×10⁻⁴ cm at T=240 K. This mechanism for electrical conductivity is compared with the hopping conductivity with a variable hopping length. The negative differential resistance in the structures examined here is found to be electrothermal in nature. Zh. éksp. Teor. Fiz. 116, 276–298 (July 1999)