Dislocations in relaxed SiGe/Si heterostructures

Recent advances in the understanding and control of threading dislocations in substantially relaxed SiGe buffer layers on Si are presented. A model fo r threading dislocation now in relaxed graded SiGe buffers is used to deter mine the potential lower limit of threading dislocation density in relaxed SiGe buffers. Greater densities than expected from the model are seen in re laxed graded alloys with final concentrations greater than 50%. We show tha t the culprits of the higher threading dislocation density are threading di slocation pile-ups. Observation of early development of pile-ups confirms t hat inhomogeneous misfit dislocation densities in the graded buffer form re gions of more severe crosshatch on the surface that impede dislocation now By using chemomechanical planarization (CMP), deleterious pile-up formation can be avoided, and previously formed pile-ups can be destroyed by regrowt h of a graded layer. Experiments with CMP and regrowth of graded layers sug gest that dislocation annihilation can be effective at reducing threading d islocation densities to densities of the order expected by the model. High quality Ge on Si layers created with the CMP process were used as templates to grow high quality GaAs on Si with strong room temperature photoluminesc ence and record minority carrier lifetime.