10 research outputs found

    Physical properties of thermoelectric zinc antimonide using first-principles calculations

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    We report first principles calculations of the structural, electronic, elastic and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material. Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic and thermodynamic properties are found to be in good agreement with experiments and they confirm the non equivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the y direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5-6 meV, similarly to what has been found in Zn4Sb3 and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects and this explains the intrinsic p-type conductivity of ZnSb.Comment: 33 pages, 8 figure

    Influence of Uniaxial Stress on the Indirect Absorption Edge in Silicon and Germanium

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    The indirect optical absorption edge in silicon and germanium has been studied in the presence of shear strain. The splitting observed in the transmission spectrum is dependent on the direction and magnitude of the applied stress and on the polarization of the light with respect to the stress axis. The results have been interpreted in terms of changes in the valence- and conduction-band structure with strain. Neglecting strain dependence of phonon energies, various deformation potential constants have been determined from the experiments. The values are: Si, 80°K: Ξu=8.6±0.2 eV, |b|=2.4±0.2 eV, |d|=5.3±0.4 eV, Ξd+1 / 3Ξu-a=3.8±0.5 eV. Si, 295°K: Ξu=9.2±0.3 eV, |b|=2.2±0.3 eV, Ξd+1 / 3Ξu-a=3.1±0.5 eV. Ge, 80°K: Ξu=16.2±0.4 eV, b=-1.8±0.3 eV, d=-3.7±0.4 eV, Ξd+1 / 3Ξu-a=-2.0±0.5 eV. An observed nonlinear dependence of the splitting on stress has been interpreted as shifts of the exciton energies with uniaxial stress. A special experimental technique using a vibrating slit in the spectrometer was used in order to obtain an accurate determination of the fine structure in the absorption spectrum

    Transport Phenomena in Heavily Doped Semiconductors

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    Single-Crystal Silicon: Electrical and Optical Properties

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