Misfit Dislocation Introduction During The Epitaxial Growth of Inas Islands on Gap
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MISFIT DISLOCATION INTRODUCTION DURING THE EPITAXIAL GROWTH OF InAs ISLANDS ON GaP Vidyut Gopal1, Alexander L. Vasiliev2, and Eric P. Kvam School of Materials Engineering, Purdue University, W. Lafayette, IN 47907 1 : Currently at Applied Materials Inc., Santa Clara, CA 95051 2 : Currently at the Institute of Materials Science, University of Connecticut, Storrs, CT 06269 ABSTRACT The initial growth of InAs on 11% lattice mismatched GaP substrates by molecular beam epitaxy was investigated. High resolution transmission electron microscopy (HREM) images showed that the InAs grew in the form of three-dimensional islands of dissimilar sizes. Mismatch induced strain relief was effected by the direct introduction of (mostly) edge dislocations at the corners of the islands. An examination of HREM images of several islands revealed that the island aspect ratio decreased with the introduction of misfit dislocations. Strain relaxation in the smaller, relatively dislocation-free islands occurred by elastic deformation of InAs lattice planes, which was more effective far from the constrained island-substrate interface. As a result, these islands grew taller and narrower, with a gradient in the elastic strain energy. However, a higher aspect ratio resulted in a higher surface area – to – volume ratio, and increased the surface energy of the InAs islands. Consequently, there was a driving force for the reduction of the aspect ratio if an alternate avenue for strain relaxation existed. The alternate route was plastic deformation by the introduction of misfit dislocations. As the island grew, the strain at the island corners increased, and beyond a critical value, misfit dislocations were added. These dislocations relieved strain at the heterointerface, and promoted the islands to grow laterally, i.e., the aspect ratio decreased. Islands coalesced, and a continuous layer resulted by a nominal thickness of 3 nm. Thus, the morphology of InAs islands grown on GaP was determined by the balance between elastic and plastic deformation. INTRODUCTION The integration of semiconductor single crystals of different band gap offers great flexibility in the design of various electronic devices. Examples include devices fabricated using the GeSi/Si system and the AlGaAs/GaAs systems. Improvements in crystal growth techniques such as molecular beam epitaxy (MBE) and metal oxide chemical vapor deposition (MOCVD) allow precise control in film composition and thickness to be achieved, especially if the mismatch in lattice constant between the overlayer film and the substrate is not very large. However, several compound semiconductors are not lattice-matched to any of the commercially available substrates. One example is InAs. It has a narrow band gap (0.36 eV) and high electron mobility (33,000 cm2/V-sec), which makes it suitable for far infra-red detecting applications, thermo-photo-voltaics, and fast transistors. Traditionally, InAs has been grown on GaAs with a lattice mismatch of ~ 7%. Here, we investigated the initial stages of the growth of InA
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