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Department of Physics, North Carolina State University, Raleigh, NC 27695. Cray Research Inc, Pittsburgh Supercomputing Center, Pittsburgh PA 15213. Institute of Physics, PAN, 02-668 Warsaw, Poland. AT&T Bell Laboratories, Murray Hill NJ 07694.

ABSTRACT We have investigated Si (100) homoepitaxy in variety of different temperature regimes. In the high temperature step flow regime, the growth properties of the different steps play an important role. The binding sites and diffusion barriers for a Si adatom moving over the buckled Si(100) surface and single-height steps were investigated with the ab initio Car-Parrinello scheme. The SA step edge was found to be a relatively poor sink for adatoms. By contrast, growth takes place much more rapidly at the SB step edges, so that one can understand the relatively fast growth observed at the ends of dimer rows. We have also investigated Si(100) homoepitaxy with classical molecular dynamics simulations at very low temperatures, where typically an amorphous deposit forms. By tuning the energy of the incoming atomic beams, one can lower the temperature of the amorphous to crystalline transition considerably and thereby enhance epitaxial growth. INTRODUCTION Epitaxial growth may be thought of as taking place in several different temperature regimes. At high temperatures and low adatom concentrations, growth takes place via a step flow mechanism. Adatoms, which have condensed on a substrate, make their way over the flat terraces via diffusion until they encounter a step edge, where they are more readily incorporated into the crystal. At intermediate temperatures and higher adatom concentrations, this process is in competition with the nucleation, growth and coalescence of islands. If the temperature is decreased even further, limited epitaxy takes place, or an amorphous deposit forms. In this paper, we present our recent work on the growth of Si on the Si(100) surface (Si homoepitaxy) in the different temperature regimes [1,2]. Clearly, at high and intermediate temperatures, the steps play an important role in the growth. Growth in this temperature regime is determined by the rate at which adatoms can reach the step edges, from either the upper, or the lower terrace. In turn, these rates are governed by the activation energies for diffusion hops. It is long been known that there may exist extra barriers at the step edge (the Schwoebel barriers). The origin of these barriers may be understood in terms of the specific geometry of a step edge, as illustrated in Fig.1, for a close-packed surface. An adatom approaching the step edge from the upper terrace must cross a region where it is relatively "far" away from the surface atoms. This is unfavorable and requires an additional activation energy. By contrast, atoms approaching

511 Mat. Roe. Soc. Syrup. Proc. Vol. 399 * 1996 Materials Research Society

Figure.1 Schematic illustrating (a) step edge and (b) the potential energy near the step edge.

(a) >,

(b)

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Distance the step edge from the lower terrace can always remain close t