Progress in creating thin film relaxed lattice constant semiconductors on conventional substrates has recently led to progress in a variety of electronic and optoelectronic devices. By understanding the relationship between misfit and threading dislocations, and the relationship between dislocation nucleation and threading dislocation propogation, graded composition buffer layers can be used to relieve lattice mismatch and retain surface layers with great perfection. A particularly interesting system is the relaxed Si 1-xGe x/Si system, which can host a variety of high performance CMOS devices as well as allow for the integration of GaAs with Si. Optical links, solar cells, and more recently, continuous wave room temperature lasers have been created on GaAs/Ge/SiGe/Si. Commercialization of relaxed Si 1-xGe x/Si materials will likely occur through the Si CMOS end market, creating a supply of low cost SiGe virtual substrates for other application areas, including solar cells.