The effects of misfit dislocation nucleation and propagation on Si/Si 1- xGe x critical thickness values

Abstract

A detailed study of the nucleation and propagation of misfit dislocations has been made in the Si/Si 1- x Ge x materials system using a standard defect revealing etch. The onset of relaxation occured at a point just above the equilibrium critical thickness limit ( h e) set by Matthews and Blakeslee. However, the majority of the material remained coherently strained for thickness values far in excess of h e. Micrographs of partially relaxed layers are presented which show that the relaxation occured in patches, with the patches gradually enlarging until they covered the complete surface. The density of these patches is shown to be directly controlled by the density of defects in the homoepitaxial silicon underlying the Si 1- x Ge x alloy layer, which, in turn, has been related to the efficacy of the oxide removal process prior to epitaxial growth. A close examination of the misfit dislocations in a partially relaxed Si/Si 0.95Ge 0.05 structure showed that each misfit line could comprise a number of individual half loops on the same slip plane. The misfit lines generally appeared as an orthogonal pair of equal length lines lying along 〈110〉 directions and intersecting at the centre points. The individual half loops nucleate at the centre of the 〈110〉 misfit lines and glide with equal speed in both directions away from the point of nucleation.