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Calculation of the Energy Spectrum of NANÖ-Meter-Sized Silicon

Published online by Cambridge University Press:  28 February 2011

Vladimir Gavrilenko ,
Peter Vogl  and
Frederick Koch
Vladimir Gavrilenko
Affiliation:
Technical University of Munich, Physics Department E16, W-8046 Garching, Germany
Peter Vogl
Affiliation:
W. Schottky Institute, Technical University of Munich, W-8046 Garching, Germany
Frederick Koch
Affiliation:
Technical University of Munich, Physics Department E16, W-8046 Garching, Germany
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Abstract

A large number of experiments on porous silicon has reliably demonstrated that the onset of optical absorption is shifted to energies significantly above the band edge of bulk Si. This increased transparency of the small nanometer-sized crystallites with their H-covered surfaces is a fact that asks for theoretical interpretation. Handwaving arguments about quantum size effect can only be a qualitative guide.

We present here a tight binding calculation of a Si slab with nanometer dimensions covered with hydrogen. This is a model system for one-dimensional confinement. We consider the effect on the electron energy structure, the total and local densities of states of Si covered with hydrogen in two phases: monohydride - Si : H (2×1) symmetric dimer, and dihydride phases - Si : Hi (1×1) A total energy minimization method in the framework of the self-consistent tight binding theory has been used to investigate the structural reconstruction of the Si -surface after the adsorption of hydrogen. We find, that the band gap of the slab covered with H on both sides (monohydride phase) shifts to higher energies (typically ∼1.8 eV for 1.16 nm thick slab). The adsorption of hydrogen removes all the electronic states from the gap for both phases investigated. In nanometer sized slabs the lowest electronic states in the conduction band are localized on the surface Si—atoms, in contrast to thicker slabs. We discuss the implication of this model calculation to light emission in porous Si.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 283: Symposium F – Microcrystalline Semiconductors–Materials Science and Devices , 1992 , 431
Copyright
Copyright © Materials Research Society 1993

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References

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