We have investigated the structural, electrical, and optical quality of epitaxial Si and SiGe films grown by MBE on SIMOX (separation by implanted oxygen) silicon substrates. Epitaxial films grown on these SOI substrates have been characterized using planar and cross-sectional TEM, SIMS, and Seeco chemical etching to delineate defects. We have fabricated the first Si/SiGe integrated waveguide-photodetector for long wavelength applications. Low reverse leakage current densities were seen in these device structures. The detector exhibited a responsivity of 0.43 A/W at 1.1 μm with an impulse response time of 200 ps. © 1991.