Reducing Threading Dislocation Densities in SiGe Mismatched Layers by Controllingc Strainc rate and Surface Roughness

Abstract

Further insight into strained layer relaxation processes have been achieved in this work. Effects of surface roughness, dislocation velocities, and dislocation nucleation have been de-coupled. In order to achieve low threading dislocation density with a high degree of relaxation, we are forced to create structures that introduce a high degree of lattice mismatch at the surface, i.e. a gradient in Ge composition in thickness. Thus, the graded layer must be introduced. However, these experiments have shed further light on the design of such structures, and we have produced relaxed layers with low threading dislocation density that are 4times less thick than their control graded composition layers