Near intrinsic single crystals of grown from the vapor have been used to construct photoconductive detectors for operation at room temperature. Fabrication of the detectors depends on the use of a newly developed chemical etch to reduce the specimens to thicknesses of a few microns, and to provide surfaces with low carrier recombination velocity. The highest detectivity, , achieved was ; Various methods of estimating bulk carrier lifetimes have been used; the value for the best crystal measured was in excess of 4 μsec. The surface recombination velocity of the best etched surface was below 80 cm sec−1. Similar etches can be used for and .