A quantitative analysis of strain relaxation by misfit dislocation glide in Si1−xGex/Si heterostructures

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Abstract
Misfit dislocation glide velocities have been measured in Si1−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.