We present the new class of the far infrared photodetectors based on the lead-tin tellurides doped with the group III impurities. The persistent photoconductivity effect appearing in these materials provides an internal signal integration resulting in a considerable increase in the signal-to-noise ratio. The techniques of the photomemory quenching are discussed. In some regime of quenching the effect of giant quantum efficiency stimulation has been observed. The possibility of generation of the photoinduced spatially nonequilibrium states provides the physical evidence for the construction of an integrating “continuous” focal-plane array based on Pb1−xSnxTe(In).