156 research outputs found

    Impact of germanium on vacancy clustering in germanium-doped silicon

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    Recent density functional theory calculations by Chen et al. [J. Appl. Phys. 103, 123519 (2008)] revealed that vacancies (V) tend to accumulate around germanium (Ge) atoms in Ge-doped silicon (Si) to form GeVn clusters. In the present study, we employ similar electronic structure calculations to predict the binding energies of GeVn and Vn clusters containing up to four V. It is verified that V are strongly attracted to pre-existing GeVn clusters. Nevertheless, by comparing with the stability of Vn clusters, we predict that the Ge contribution to the binding energy of the GeVn clusters is limited. We use mass action analysis to quantify the relative concentrations of GeVn and Vn clusters over a wide temperature range: Vn clusters dominate in Ge-doped Si under realistic conditions

    Diffusion of n-type dopants in germanium

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    Concentration of intrinsic defects and self-diffusion in GaSb

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    Early experiments have determined that the gallium and antimony diffusivities in gallium antimonide are similar, whereas recent more precise studies demonstrate that gallium diffuses up to three orders of magnitude faster than antimony. In the present study using electronic structure calculations we predict the concentrations and migration enthalpy barriers of important defects in gallium antimonide. It is predicted that the asymmetric self-diffusion in gallium antimonide is due to the insufficient concentration of the point defects that can facilitate the antimony transport. The results are in excellent agreement with the recent experimental evidence and theoretical studies in gallium antimonide and related materials. (c) 2008 American Institute of Physics

    <i>E</i> centers in ternary Si<sub>1-<i>x-y</i></sub>Ge<sub><i>x</i></sub>Sn<sub><i>y</i></sub> random alloys

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    Density functional theory calculations are used to study the association of arsenic (As) atoms to lattice vacancies and the formation of As-vacancy pairs, known as E centers, in the random Si0.375Ge0.5Sn0.125 alloy. The local environments are described by 32-atom special quasirandom structures that represent random Si1-x-yGexSny alloys. It is predicted that the nearest-neighbor environment will exert a strong influence on the stability of E centers in ternary Si0.375Ge0.5Sn0.125

    Defect interactions in Sn<sub>1-<i>x</i></sub>Ge<sub><i>x</i></sub> random alloys

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    Sn1-xGex alloys are candidates for buffer layers to match the lattices of III-V or II-VI compounds with Si or Ge for microelectronic or optoelectronic applications. In the present work electronic structure calculations are used to study relative energies of clusters formed between Sn atoms and lattice vacancies in Ge that relate to alloys of low Sn content. We also establish that the special quasirandom structure approach correctly describes the random alloy nature of Sn1-xGex with higher Sn content. In particular, the calculated deviations of the lattice parameters from Vegard's Law are consistent with experimental results

    Diffusion of E centers in germanium predicted using GGA+U approach

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    Density functional theory calculations (based on GGA+U approach) are used to investigate the formation and diffusion of donor-vacancy pairs (E centers) in germanium. We conclude that depending upon the Fermi energy, E centers that incorporate for phosphorous and arsenic can form in their neutral, singly negatively or doubly negatively charged states whereas with antimony only the neutral or doubly negatively charged states are predicted. The activation energies of diffusion are compared with recent experimental work and support the idea that smaller donor atoms exhibit higher diffusion activation energies

    Fluorine codoping in germanium to suppress donor diffusion and deactivation

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    Electronic structure calculations are used to investigate the stability of fluorine-vacancy (Fn)Vm) clusters in germanium (Ge). Using mass action analysis, it is predicted that the FnVm clusters can remediate the concentration of free V considerably. Importantly, we find that F and P codoping leads to a reduction in the concentration of donor-vacancy (DV) pairs. These pairs are responsible for the atomic transport and the formation of DnV clusters that lead to a deactivation of donor atoms. The predictions are technologically significant as they point toward an approach by which V-mediated donor diffusion and the formation of inactive D(n)V clusters can be suppressed. This would result in shallow and fully electrically active n-type doped regions in Ge-based electronic devices
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