Silicon-gemanium is a promising materials system for delivering near-IR photodetection on the ubiquitous silicon substrate. The 4% lattice mismatch leads to biaxial strain for SiGe films grown coherently on (100) Si substrates, which both extends the long wavelength detection limit by reducing the band gap and defines the critical thickness for the SiGe film. We have studied the use of strained-layer superlattices grown on high quality relaxed SiGe buffers. Graded buffers are ideal virtual substrates for achieving a complete range of compositions and strains for GeSi alloys. A physical model has been created to map out the absorption coefficient as a function of Ge fraction and (100) biaxial strain. Based on calculated absorption spectra as a function of composition and strain, we have designed and grown a Ge/Ge0.5Si0.5 strain-balanced superlattice on a high quality Ge0.75Si0.25 relaxed buffer using UHV-CVD. The strain-balanced superlattice has an effective absorption coefficient of 5000 cm−1. The relaxed buffer serves as a virtual substrate with relatively low threading dislocation density (106 cm-−2). The effect of the threading dislocations on the leakage current of P-I-N junctions is also investigated. Electron beam induced current (EBIC) is used to determine the dislocation density of SiGe relaxed buffer junctions grown with different grading rates. Mesa isolated devices are used to determine bulk leakage current densities for the SiGe junctions. The bulk leakage current density scales directly with the dislocation density. Bulk leakage currents density per dislocation length (2×10−5 A cml) agrees with deep level transient spectroscopy (DLTS) determined literature values for SiGe capture cross-section and defect density per dislocation in Si.