Nucleation of dislocation loops in strained epitaxial layers

Abstract

The combined effect of the misfit strain and the strain caused by a neighboring defect on the activation energy of nucleation of dislocation loops is calculated. Defects of different sizes and shapes and located at different distances from the loop are considered. At very low mismatches (<0.5%) and with very small defects, the activation energy is not sufficiently reduced and large layer thicknesses are required for nucleation. At mismatches of 1% or more, and with defect sizes of 1.5 nm or larger, heterogeneous nucleation at growth temperatures becomes possible. These defects are more efficient in reducing the energy when they are at the center of the loop. Though impurities located within the core of the dislocations can reduce the core parameter substantially and therefore reduce the activation energy, in practice this is unlikely to occur. Very large defects such as SiO2 and SiC precipitates reduce the activation energy of nucleation over large distances thereby inducing the nucleation of several loops which results in very rapid relaxation of strain. In highly mismatched layers (4%–8%) homogeneous nucleation occurs at about 400–500 °C. Why the periodic arrangement of misfit dislocations is observed only in the highly mismatched layers is explained.

Fabrication technology of SiGe hetero-structures and their properties

“…An activation barrier for homogeneous nucleation of surface dislocation half-loops was calculated for SiGe/Si(0 0 1) systems, and it was shown to be sensitively influenced by Ge contents, i.e., strain, and the dislocation core energy parameter [78]. Consensus of qualitative arguments reached that homogeneous nucleation of half-loops is physically plausible at moderate and high mismatches while heterogeneous nucleation relevant to a neighboring defect operates at low mismatch [79]. Furthermore, the aforementioned perturbation formed on the film surface plays a crucial role in the dislocation nucleation.…”

Stresses and strains in epilayers, stripes and quantum structures of III - V compound semiconductors

“…and b is the Burgers vector, b 1 = b cos β, q is the core cut-off parameter, and is assumed to be equal to b, and ρ c is the core energy parameter. β is the angle between the dislocation line and its Burgers vector and has a value 60 2 but by a different mechanism [72]. Below h c the line tension, i.e.…”

“…If defects which act as sources for dislocation generation are absent (i.e. the layers are of high quality), nucleation is homogeneous and needs large energy [72]. It becomes another factor which limits the generation of dislocations.…”

“…Recently Jain et al [72] have discussed the homogeneous and heterogeneous nucleation in strained epilayers and have given an extensive list of references on the subject. The energy needed for nucleation at low mismatch (< 1%) is very high, of the order of 100 eV.…”

“…These defects include interstitially strained platelets, interface inhomogeneities, carbon precipitates and structural defects. Jain et al [72] have given a theory to determine the reduction in the energy of nucleation for a given size, shape and location of the defect. They have shown that a defect as small as 1.5 nm in size will make the nucleation possible at a mismatch of 1%.…”