Defects in Silicon-Germanium Strained Epitaxial Layers

Abstract

<p>The energies of one and two-dimensional dislocation arrays lying near<br />a free surface are evaluated directly from the stress fields of single dislocations<br />in a half-space. These results are used to obtain expressions giving the<br />equilibrium spacings of a number of different arrays relieving misfit in a<br />strained epitaxial system. Numerical calculations are performed for the case of<br />edge and 60º dislocations relieving strain in a silicon-germanium layer<br />deposited on a silicon substrate. This method is also used to calculate the<br />energies of various low angle grain boundaries in a half-space.</p> <p>Single-ended dislocation sources are observed using transmission<br />electron microscopy in two short-period Si-Ge superlattices grown on Si(100).<br />Their formation is linked to the development of non-planar layers during the<br />growth of the superlattices. The relaxation of these superlattices takes place<br />at significantly lower temperatures than equivalently strained homogeneous<br />epilayers.</p> <p>Si-Ge short period superlattices deposited on Si(100) are shown to<br />relax through twinning on {111} planes if the deposited layers become grossly<br />non-planar. Twinning is accompanied by the formation of a diamond<br />hexagonal phase. No 60· a/2(110) dislocations relieving misfit are present in the strained layer structure.</p> <p>The nature and origin of a new type of defect in Si₁_ᵪGeᵪ/Si strained<br />layer structures, the "pagoda" defect, is studied using transmission electron<br />microscopy. The defects are found to propagate in a direction determined by<br />the position of the Si source in unrotated substrates, and to have their origin<br />in the role played by SiC particles (left after cleaning the substrate) during<br />the growth process. Pits that form at the SiC particles are preserved during<br />MBE growth and perturb the strained layers, leading to the formation of<br />pagodas.</p>