Misfit Dislocations and Elastic Relaxation
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surface morphology is driven by the reduction of the strain energy in the layer. In consequence an inhomogeneous strain and stress distribution within the layers arises which is to be accounted for when considering plastic relaxation processes due to misfit dislocation nucleation and extention in addition to these elastic ones. This mutual dependence of elastic and plastic relaxation phenomena was for long time not recognized and misfit dislocation behavior, was discussed for planar misfitting systems essentially on the basis of Matthews and co-authors work, eg [1]. The inherent instability of strained layers was, however, known already from the work of Asaro und Tiller [2], Mullins [3,4] and, some time later, discussed by Grinfeld, eg. [5]. It received attention in strained semiconductor layer growth when optimized growth conditions permitted to obtain strained layers with inhibited nucleation of misfit dislocations. Experimentally Cullis et al. were first to perform a thourough analysis of rippling in the system Sil-. Gex/Si by careful electron and scanning probe microscopies. Evidence for cusping was put forward from electron microscopy by Jesson et al. [7] and first direct evidence for dislocation nucleation in the enhanced stress field near the valleys of undulations was recently presented by Cullis et al. [8] and Albrecht et al. [9]. Analogous work on plastic relaxation in islands is a little more numerous, and rendered valuable insight into dislocation behavior, eg [10-12] which will not be detailed here. A large body of theoretical work in recent years, essentially by linear stability analysis using various mathematical approaches to the energy minimization of undulating strained layers has established the wavelength range of instable perturbations (eg. [14-171). Extrapolation of these stability analyses and assessment of the temporal development, with proper consideration of the 313 Mat. Res. Soc. Symp. Proc. Vol. 399 ©1996 Materials Research Society
nonlinear character [17], showed that during growth these instabilities will increase and eventually lead to the development of crack-like cusps. Recently, within these approaches, also nucleation
of dislocations at cusps was considered [19-22]. Most of this theoretical work concerns twodimensional (2D) models, however, describes the physical essence of the 3D case as well, eg. [15,23].
In view of these theoretical efforts, there is some need for experimental results on the development of growth topology and misfit dislocation formation. The experimental work considered above and other work concerns mostly rather high misfit systems, say in the order of 1 %, and we in the following report on observations in the system Si 0 ,97 Ge0 ,03/Si (001) with a
misfit of only 0,12 %. The main aspect of this work is that the layers are grown from metallic indium solution (liquid phase epitaxy) and, due to the facilitated diffusion from the liquid to the growing surface and also parallel to the solid-liquid interface [24], kinetic restrictions in morphology evolution
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