A QUANTITATIVE-ANALYSIS OF STRAIN RELAXATION BY MISFIT DISLOCATION GLIDE IN SI1-XGEX/SI HETEROSTRUCTURES

Misfit dislocation glide velocities have been measured in Si 1-xGex/Si heterostructures. Dislocations were deliberately introduced at sites of crystalline damage, the samples were then annealed, and dislocation propagation distances measured using defect selective chemical etching. A number of different sample configurations were investigated with different layer thicknesses and alloy compositions. The measured velocities were found to depend on a number of factors including anneal temperature, an activation energy (which was found to depend on the Ge mole fraction), the effective misfit stress (which is a function of the Ge mole fraction and layer thickness), and the length of the threading arm of the misfit dislocation. Si/Si1-xGex/Si buried-layer structures typical of the heterojunction bipolar transistor were also studied. Two possible relaxation mechanisms, involving two- and three-segment dislocation configurations, are considered and an evaluation of the most likely mechanism for a range of different structures is presented. A complete quantitative analysis is made of all the results and expressions have been derived for the misfit dislocation glide velocity as a function of layer thickness and alloy concentration for all types of layer configuration.