Compositional Modulation and Ordering in Semiconductors
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Compositional Modulation and Ordering in Semiconductors Thomas P. Pearsall and Gerald B. Stringfellow, Guest Editors The science of materials as a specific discipline is a relatively modern development. Within this rather modern field, the study of semiconductor materials is an even more recent development. Modern textbooks on materials science focus primarily on the properties of metals and second on the properties of ceramics, reflecting the commercial importance of these materials 50 years ago when the transistor was demonstrated using germanium. Today the commercial importance of semiconductor materials is comparable to that of metals and ceramics, and the advances in semiconductormaterials technology are driving rapidly growing business sectors in communications, software, and biotechnology. Almost all semiconductor devices are based on the control and manipulation of electrons and holes in thin-film structures. These structures are produced commercially in elemental semiconductors like silicon and in semiconductor-alloy structures like Si*Gei-_T or GaxIni-AAs, for example. Semiconductor alloys have materials properties that can be understood often in terms of similar behavior observed in systems of metal alloys. This is certainly the case with some of the phenomena discussed in this issue, such as solid-phase immiscibility and longrange ordering. However the study of the epitaxial growth of these alloys has also uncovered new materials-growth phenomena that are driven by the highly directional and largely covalent nature of the bonding in semiconductors. There is a large strain energy associated with the stretching and bending of bonds on the atomic scale in semiconductor alloys. This energy is an important factor in de16
MRS BULLETIN/JULY 1997
Compositional Modulation and Ordering in Semiconductors
efficients. These changes reflect the symmetry of the surface reconstruction so that anisotropy is introduced into surface diffusion. A direct result of this anisotropy is a long-range periodic modulation of the composition oriented along specific crystallographic directions. The article by J. Mirecki-Millunchick along with workers at Sandia National Laboratories and NREL describes the longrange lateral ordering that results from this strain-induced surface reconstruction during crystal growth by molecularbeam epitaxy. The period of long-range ordering is determined by a complex
Thomas P. Pearsall is a professor and BoeingJohnson Chair at the University of Washington where he holds positions in the Department of Electrical Engineering, •he Department of Materials Science and Engineering, and the Department of Physics. He is a Fellow of the American Physical Society and the Institute of Electrical and Electronics Engineers. He was recently named Fulbright Senior Scholar and is studying electronic transport in high magnetic fields at the Centre National de la Recherche Scientifique in Grenoble, France. Pearsall can be reached at the Department of Materials Science and Engineering, University of Washington, Seatt
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