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535 Mat. Res. Soc. Symp. Proc. Vol. 317. ©1994 Materials Research Society

helpful in engineering these defects - for example rendering them electrically inactive. Earlier we simulated some typically observed surface defects (grain boundaries) in diamond films (2). Computer simulations can also narrow the choices that can be made for the susbtrate orientation and type. A potential gradient can be effectively simulated for successful epitaxial growth. In this study, we have used computer simulations to investigate the energetics of different configurations of a diamond film on a silicon substrate. The minimum energy configuration identified from simulations is compared with experimental depositions of C on Si. METHODS A 486 DX2/66MHz personal computer was used for simulations. A commercially available software package ADESH (Atomistic DEfect Simulation Handler -- Vendor: CASA, Hopewell Junction, NY, USA) running under DOS, was used for simulations. A diamond crystal and a silicon substrate with (100) orientation were created separately and then fitted together. The interface was adjusted to minimize energy and/or to eliminate the dangling bonds. This was accomplished by rotating and moving the film against the substrate, applying strain to the film, and by editing/relaxing atomic positions at the interface. Several configurations were tried by first rotating the film about the axis perpendicular to the substrate through various angles and then moving the film rigidly against the substrate. To maintain coherency, the interplanar distance of parallel crystallographic planes in substrate and film was matched by applying strain where necessary. Finally, individual atom relaxations were used to minimize the energy of each configuration. Energy was calculated by Tersoff (3) potential functions. This potential function has a cutoff between second and third nearest neighbor (3). Energy contributions from atoms beyond this distance are ignored. Geometric average values for parameters of silicon and diamond were used across the interface where some atoms had dissimilar atoms as immediate neighbors. After minimum energy configurations were computed, the resulting structures were analyzed for average energy per atom and dangling bonds in atomic layers near the interface (Table I). We investigated four configurations, called Structures A, B, C and D, of the interface. The first three structures have silicon substrates and diamond film. The Structure D used SiC as a substrate to investigate the possibility of alloying between silicon and diamond. Finally, diamond thin films were deposited onto silicon substrate. Hot filament chemical vapor deposition technique was used with filament temperature to be 20000 C. The substrate temperature was 850 0 C. Methane and Hydrogen gases were used with 0.5% methane in the mixture. Chamber pressure was 22 Torr. The structure was characterized with transmission electron microscope. We used Akashi 002B at 200KV.

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RESULTS Atomislic Approach Structure A (Figure 1), is similar to the one descr