Structural and vibrational properties of carbon impurities in crystalline silicon

Abstract

Si 1−x C x alloys have been studied using self-consistent-charge density-functional-based tight-binding calculations. The origin of experimentally observed carbon-induced vibrational peaks near 475, 607 and 810 cm −1 are analysed, based on the theoretical calculations. The stability, vibrational frequencies, lattice relaxations, and energy gap variances of substitutional, interstitial single-carbon and dicarbon complexes in crystalline silicon are calculated. All the impurities induce severe lattice relaxations of adjacent Si atoms. The peak near 475 cm −1 originates from the lattice relaxations of Si atoms up to second-nearest neighbours from carbon impurities in all cases. The peak near 605 cm −1 originates mainly from the midbond interstitial carbon (which is at odds with general belief) whereas the high-energy peaks near 810 cm −1 result from the formation of the carbon complexes.

SiH2adsorption on the single dimer vacancy of the Si(100) surface

“…These schemes introduce the parameters from the first-principles calculation and experimental results. It has proved to be both efficient and accurate enough in studying various Si-H systems [7][8][9][10][11][12][13][14][15][16].…”

The bonding configuration in a partially relaxed pseudomorphic epilayer of SiGe: evidence of the BC-8 phase of silicon

“…One of the situations is that carbon occupying the substitutional sites C sub (figure 5(A)), where the total energy minimization yields a configuration in which the Si-C bond is longer (∼2.03 Å) than the normal SiC (1.91 Å). The bond angle between the C sub and the adjacent silicon neighbours is 110 • , close to that of the tetrahedral sp 3 bonded silicon (109.5 • ) [25]. Thus the Raman peak at ∼615 cm −1 is related to carbon occupying these C sub sites, as at low concentration most of the carbon goes into substitutional positions.…”

“…This will result in asymmetric Si-C bonds (namely 1.76 and 1.83 Å) and Si-Si back bonds (having bond lengths of ∼2.29 and 2.46 Å quite different from that of an ideal one). The bond angle around this mid-bond carbon atom, can be as large as 124 • favouring an sp 2 kind of re-hybridization [25]. The Raman peak at ∼670 cm −1 may be associated with this kind of configuration.…”

“…The self-consistent charge density-functional-based tight binding method employed by Zhu et al [25], indicates that the carbon incorporation in silicon can generate a variety of geometrical re-arrangements. One of the situations is that carbon occupying the substitutional sites C sub (figure 5(A)), where the total energy minimization yields a configuration in which the Si-C bond is longer (∼2.03 Å) than the normal SiC (1.91 Å).…”

“…Thus the Raman peak at ∼615 cm −1 is related to carbon occupying these C sub sites, as at low concentration most of the carbon goes into substitutional positions. The carbon atom can however also exist at an interstitial position (C int ), located midway between the Si atoms of the two tetrahedra (figure 5(B)) [25]. This will result in asymmetric Si-C bonds (namely 1.76 and 1.83 Å) and Si-Si back bonds (having bond lengths of ∼2.29 and 2.46 Å quite different from that of an ideal one).…”