Plastic Relaxation Mechanics in Systems with a Twist-Bonded Layer
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I13.4.1
Plastic Relaxation Mechanics in Systems with a Twist-Bonded Layer Catherine Priester1 and Geneviève Grenet2, IEMN/ISEN, CNRS-UMR 8520, BP 69 F-59625, Villeneuve d'Ascq Cedex, FRANCE. 2 ECL/LEOM, CNRS-UMR 5512, BP 163 F-69131, Ecully, Cedex, FRANCE 1
ABSTRACT With a view to investigating how a thin film twist-bonded to a host substrate can have compliant behavior from a plasticity point of view, the onset and spread of edge dislocations throughout a mesa are studied. The discussion focuses on the energy relaxed by such dislocations in a mesa made from two coherently bonded lattice-mismatched layers twist-bonded onto a host substrate and patterned down to the film/host substrate interface. Our theoretical results show that the confinement of threading dislocations into a thin twist-bonded film is energetically favorable allowing the overgrowth of a mismatched layer exempt of any threading dislocation at least as far as mesas are concerned. INTRODUCTION Manufacturing high-performance optoelectronic devices requires the growth of semiconductor heterostructures exempt of any defects, especially those that result from stress relaxation. Actually, such manufacture is inhibited by the lack of appropriate substrates allowing the growth of highly lattice-mismatched heterostructures. Indeed, when a film is grown latticemismatched on a substrate by techniques like MBE (Molecular Beam Epitaxy), its stress energy increases with thickness up to a critical point beyond which it has to be released by either an elastic (formation of dots) or a plastic (formation of dislocations) process. Therefore, engineering a somewhat “universal” substrate, i.e., “compliant” with any kind of epitaxial growth is currently one of the most challenging goals in materials research for optoelectronics [1-5]. In 1991, Lo [1] initiated the subject by suggesting the use of a thin film as substrate. As a matter of fact, the law ruling the way the elastic energy is shared by the two films means the thicker will impose its own lattice parameter onto the thinner, which will therefore sustain most of the defects arising from stress relaxation. The next problem to be solved is the unavoidable curvature and the difficult mechanical handling of such an ultra thin heterostructure. Several solutions have already been proposed to tackle this problem, most of them involve sticking the compliant substrate on a thick host substrate. The way this sticking is done reveals the way the relaxation is presumed to act. If an intermediate viscous layer is used to stick the compliant layer to its host substrate, an elastic relaxation is guessed acting [6,7] whereas any attempt to weaken the interface by for example twisting and/or tilting the compliant axes relative to the host substrate ones means that some kind of plastic relaxation is expected [8-13]. In this study, we concentrate on the plastic relaxation undergone by a heterostructure made of two lattice-mismatched layers, twist-bonded to a host substrate. At this point, it is worth noting that when dealing with t
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