Transferable Tight-Binding Approach Of Si-H Interactions
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Eunja Kim', Seung Mi Leeb, and Young Hee Leeb'c "Dept. of Physics, University of Nevada, Las Vegas, NV 89154 bDepartment of Semiconductor Science and Technology, Jeonju 561-756 cDept. of Physics and Semiconductor Physics Research Center, Jeonju 561-756
ABSTRACT
We construct transferable tight-binding parameters of silicon-hydrogen interactions, reproducing the electronic energy levels and vibrational frequencies of the silane(SiH 4 ) molecule accurately. The potential function was rescaled with the exponential factor in order to ensure that the potential energy is smooth at an appropriate cut-off distance, which is very important in molecular-dynamics simulations. The parameters have been applied to other molecules and various surfaces such as hydrogenated Si(100) surfaces, for example, monohydride, dihydride, and (3xl) phase. INTRODUCTION
The roles of hydrogen atoms in semiconductor materials are not only interesting physical phenomena but also very important to understand in device technology, because hydrogen is generally known to passivate surfaces and amorphous silicon(a-Si) by saturating the dangling bonds, changing the electrical and optical properties. [1] Especially, hydrogen plays an important role in layer-by-layer epitaxial growth of Ge on Si(100) surface. [2,3] In this
case the surface morphology of Si overlayers strongly depends on surface H coverage. [4] Despite the fact of the abundant appearance in many H-Si systems, the physical mechanism underlying these phenomena is still far from being completely understood. First principles approaches have been successfully applied to hydrogen in bulk Si and Si surfaces within the local density approximation(LDA). [5 7] Moreover, Car-Parrinello molecular-dynamics (CPMD) simulations [8] have also made a big step in further understanding of hydrogenated a-Si. [9] However, this method is limited to a small number of atoms, and the computational cost is still expensive for some dynamical properties. Although classical potentials have been proposed in hydrogenated a-Si [10], due to the low computational cost, the reliability cannot be guaranteed since it does not include the electronic information in total energy calculation. Therefore, several empirical tight-binding (TB) models have been proposed. [11,12] Since the TB scheme considers only the valence electrons in the electronic structure calculations and the overlap integrals are empirically fitted to the first principles calculations or experiments, both the accuracy and efficiency have been achieved. Although the TB model by Min et el. [12] takes account of the anharmonic effect by implementing the universal binding energy curve in the fitting procedure, the simple inverse scaling law of the distance still causes 347
Mat. Res. Soc. Symp. Proc. Vol. 491 ©1998 Materials Research Society
undesirable effects particularly in describing hydrogen dynamics and absorption-desorption processes. Therefore, a new model is generally required to have a smooth potential function behavior at an appropriate cutoff dista
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