Prototype detector structures were fabricated on Si substrates using Ge1-ySny as active material for the first time. This alloy system covers the entire near-IR telecommunication spectrum and grows at a low temperature of 350 degrees C, compatible with complementary metal-oxide-semiconductor (CMOS) Si technology. Processing protocols were developed for photolithography-based patterning and subsequent etching, CMOS compatible metallization, and for the formation of low-resistivity Ohmic contacts. A first generation of devices based on as-grown Ge1-ySny layers was followed by a second generation incorporating ex situ rapid thermal annealing for defect reduction, as well as additional growth and processing improvements, leading to enhanced mobilities and simultaneous reduction in intrinsic carrier concentrations. While both device generations show a significant photoconductive response at 1.55 mu m, the thicker second-generation samples yield improved performance due to better confinement of deleterious defects near the interface, which increases the optically active fraction of the film.