Pb(0.9)Sn(0.1)Se thin films were deposited onto cleaved (111) CaF(2) and BaF(2) substrates by either an open one-boat evaporation method or a Knudson type graphite boat method. On CaF(2), single crystal (100), (111), and polycrystalline (100)+(111) films were obtained. On BaF(2), single crystal (111) and polycrystalline (111)+(100) films were achieved. As-deposited films were not photosensitive. Photoconductivity was observed after isothermal annealing in Pb/Sn rich vapor to reduce their carrier concentrations to the mid-10(16) to mid-10(17) range. (100) films were more sensitive than either single crystal (111) or polycrystalline (100)+(111) films. At 100°K, 500°K blackbody responsivities up to 60V/W have been developed, compared with the best blackbody responsivities around 100-125 V/W reported for commercial photovoltaic detectors of Pb(1-x) Sn(1)Te operated at 77°K.http://archive.org/details/thinfilmpb09sn0100mcbrCaptain, United States Marine CorpsApproved for public release; distribution is unlimited.