Photoconductive PbSe films were grown epitaxially on NaCl and KCl substrates. The films had hole concentrations as low as 9×1016 cm−3 and Hall mobilities as high as 15 000 cm2 V−1 sec−1 at 77 K. Nearly strain-free films were prepared by transferring them from alkali-halide substrates to a plastic with almost the same thermal expansion coefficient as PbSe. These films retain high mobilities, are unaffected by moisture, and can be cycled between 300 and 77 K. The plastic-mounted films have a cutoff wavelength of 4.4 μ at 300 K and 6.4 μ at 77 K corresponding to the optical energy gap of bulk PbSe. In contrast, the response of films on NaCl and KCl extends to 8.3 μ at 77 K corresponding to the optical energy gap of highly strained PbSe. The blackbody responsivities of the most sensitive films increase monotonically from 0.2 V/W at 300 K to 4 V/W at 77 K. Response times, measured with a GaAs laser, are 2×10−7 sec, and photoconductive lifetimes calculated from the responsivities are 7×10−7 sec at 77 K. Peak detectivities at 77 K are 8×108 cm Hz12 W−1 and are Johnson-noise-limited at 2 KHz.