The Roles of Stress, Geometry and Orientation on Misfit Dislocations Kinetics and Energetics in Epitaxial Strained Layer
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THE ROLES OF STRESS, GEOMETRY AND ORIENTATION ON MISFIT DISLOCATIONS KINETICS AND ENERGETICS IN EPITAXIAL STRAINED LAYERS. R. Hull, J.C. Bean, F. Ross, D. Bahnck and L.J. Peticolas.
AT&T Bell Laboratories 600 Mountain Avenue Murray Hill, NJ 07974 ABSTRACT The geometries, microstructures, energetics and kinetics of misfit dislocations as functions of surface orientation and the magnitude of strain/stress are investigated experimentally and theoretically. Examples are drawn from (100), (110) and (111) surfaces and from the Ge, Sii-,d/Si and In 5 Gal_,/GaAs systems. It is shown that the misfit dislocation geometries and microstructures at lattice mismatch stresses < -1 GPa may in general be predicted by operation of the minimum magnitude Burgers vector slipping on the widest spaced planes. At stresses of the order several GPa, however, new dislocation systems may become operative with either modified Burgers vectors or slip systems. Dissociation of total misfit dislocations into partial dislocations is found to play a crucial role in strain relaxation, on surfaces other than (100) under compressive stress.
1. INTRODUCTION Successful epitaxial growth of lattice-mismatched semiconductor materials combinations offers new opportunities in combining and modifying structural and electronic parameters (see e.g. [1]). The thickness to which an epitaxial layer may be grown before elastic strain energy is relieved via formation of misfit dislocations is known as the "critical thickness", h,. The magnitude of this critical thickness has been calculated using equilibrium theory by a large number of authors (e.g. [2]-[5]). Finite misfit dislocation nucleation and propagation rates ensure that when the critical thickness is exceeded, the structure does not instantaneously achieve its equilibrium strain state at finite temperatures [6]. Rather, the structure may be grown to substantially greater thickness than equilibrium critical thickness predictions, before detectable densities of misfit dislocations are observed [6],[7]. This "metastable" growth regime is encouraged by lower growth temperatures, higher inter-atomic potential (Peierl's) barriers to dislocation motion, and higher energy barriers for dislocation nucleation. A classic example of this metastable growth regime is in the Gex SitI.. 5/Si(100) system at a growth temperature of 550'C [8] , where for relatively dilute Ge concentrations, epilayer thicknesses may be grown to an order of magnitude greater than equilibrium predictions of hc before misfit dislocations are present in substantial densities. Increasing the growth temperature (e.g. to 750'C in the GexSi I 5 /Si system [9], ), decreasing the Peierls barrier (e.g. by comparison to another system such as ln 5 0Gal-/GaAs [10], increasing the available dislocation source density (e.g. [11] ) or increasing the experimental sensitivity to dislocations (e.g. [12] ), all compress the apparent metastable regime. Much theoretical and experimental progress in modelling and understanding the kinetics of strain relief has been
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