Photoconductivity kinetics in high resistivity n-PbTe(Ga) epitaxial films

We present a study of photoelectric and kinetic properties of n-PbTe(Ga) epitaxial films prepared by the hot wall technique on BaF2 and SiO2-Si substrates. The measurements were performed under continuous and pulse illumination with use of a heat source and LED in the temperature range 4.2-300 K. The investigated samples were highly sensitive to infrared illumination at temperatures lower than 100-110 K. Two characteristic regions were clearly resolved in photoconductivity relaxation curves: a fast one at the beginning of relaxation (with lifetimes of about 10(-3) s at 4.2 K) and a long duration relaxation tail. The obtained results are discussed in terms of the configuration diagram of a DX-like centre in PbTe(Ga). The experimental data obtained for the films are compared with properties of bulk material.