First-principles total-energy calculations of atomic and electronic structure in relaxed Si1-x-yGexCy

M. Ohfuti, M. Ikeda, Yuji Awano, N. Yokoyama

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Abstract

We analyzed the atomic and electronic structures in relaxed Si1-x-yGexCy crystals using first-principles total energy calculations. First, to investigate the dependence of properties on C and Ge concentrations, uniform alloys with y=0, 0.0625, 0.125, and 0.5 were examined. It was found that the total energy when C atoms are surrounded by Si atoms (Type A) is lower than that when they are surrounded by Ge atoms (Type B) because of the larger gain in chemical binding energy in spite of the larger distortion energy. The band gaps are reduced for y=0.0625 and 0.125 from those for y=0, indicating a finite gap (semiconductor) for Type-A structure but no band gap for Type-B structure. In the semiconducting alloys of Type A, the effective masses of heavy holes become smaller. The alloy crystals with y=0.0625 have direct band gaps, and the oscillator strengths of the optical transition between the band-edge states are much larger than for Si1-xGex systems without a C atom, because of the C s-orbital component in the bottom of the conduction bands. Next, to extend these results to random alloys, five C arrangements of Si1-yCy alloys were examined. The reduction of effective hole mass does not depend on the C arrangements. Every crystal has a direct band gap with C s-orbital component at the conduction-band bottom, leading to high-optical transition as in the uniform alloy. Finally, the band structure of the alloys were systematically described based on the tight-binding expression, which speculated that the band gap of the random alloy might be larger than that of the uniform alloy.

Original languageEnglish
Pages (from-to)13547-13554
Number of pages8
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume60
Issue number19
Publication statusPublished - 1999
Externally publishedYes

Fingerprint

Crystal atomic structure
atomic structure
Electronic structure
electronic structure
Energy gap
energy
Atoms
Optical transitions
Conduction bands
optical transition
Crystals
atoms
conduction bands
crystals
orbitals
Binding energy
oscillator strengths
Band structure
binding energy
Semiconductor materials

ASJC Scopus subject areas

  • Condensed Matter Physics

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First-principles total-energy calculations of atomic and electronic structure in relaxed Si1-x-yGexCy. / Ohfuti, M.; Ikeda, M.; Awano, Yuji; Yokoyama, N.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 60, No. 19, 1999, p. 13547-13554.

Research output: Contribution to journalArticle

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