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Home  >  Volume 26 (March 2014)

25. Ab Initio Study of the Electronic Structure of Silicon Quantum DOTS by Sylvester A. Ekong, I. A. Fuwape, and E. A. Odo. Volume26, (March, 2014), pp 177 – 186.
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Abstract

In this work, first principle calculation was performed on three nanostructures of hydrogenterminated silicon quantum dots namely: (a) (b) and (c) .Calculations on structural relaxation using DFT self-consistent total energy scheme with a convergence criterion of the Hellman-Feynman forces set at 1meV/Å; and plane wave basis with kinetic energycut-off energy of 35Ry integrated over a Brilloun zone of uniform grid of 5x5x5 points was also performed .The variation of the ground state total system energy with the planewavecutoff energy, K–Points, and lattice constant were graphically analysed. The results obtained shows that the ground state total system energy have a local minimum for a range of theplanewavecutoff energy, K–points, and lattice parameter values. The Si–Si and Si–H bond lengths are approximately structurally size independent; whereas the bond angles appear to have small size dependence. Also, the lattice parameter and equilibrium volume increases linearly with molecular size; whereas the bulk modulus and equilibrium energy decreases with increasing size of the silicon quantum dots. The band structure calculation reveals distinctively, a discretization of energy levels in the band structure due to quantum confinement as well as a shift from the indirect HOMO–LUMO energy gap found in bulk silicon to a direct one. The size of the energy gap was also observed to decrease with increasing quantum dot size.Furthermore, the results obtained in this work are in good agreement with other theoretical quantum dot models as well as those obtainedfrom experimental data, showing that this model can be used to predict both structural and electronic properties of silicon quantum dots in this size range.

Keywords:Supercell, QD, HOMO, LUMO, Geometrically optimized structures

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