Transport properties and photoconductivity of nanocrystalline PbTe(In) films

Microstructure, charge transport and photoelectric properties are studied for PbTe(In) films deposited on amorphous substrates kept at different temperatures T_s during deposition. All the films have a column-like structure with the mean column diameter increasing from 60 nm at the lowest T_s = -120°C up to 300 nm at the maximal T_s =250°C. The substrate temperature increase results in appearance of a preferred orientation of grains and in an inversion of the conductivity type from hole to electron. Electric transport and photoelectric properties of the films were studied in the temperature interval 4.2 - 300 K in DC and AC modes at frequencies varied from 20 Hz up to 1 MHz. The impedance spectra analysis was done in terms of the equivalent circuit model. Modification of charge transport mechanisms is correlated with the variation of microstructure of the films grown at different substrate temperatures. Films with disordered grains possess all features of non-homogeneous systems, while the films with a preferred orientation of grains are analogous to PbTe(In) single crystals in their transport and photoelectric properties. Mechanisms of the persistent photoconductivity observed in the films are qualitatively distinguished.