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  • 1
    Electronic Resource
    Electronic Resource
    Virtual charge method for electrostatic calculations in metallic tip and semiconducting sample systems (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5589-5596 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We calculate the electrostatic field between a metallic tip and a semiconductor surface by replacing the electrodes by a set of virtual charges, adjusted to fit the boundary conditions on the surfaces. The boundary conditions on the semiconductor side of the surface are obtained by using the result of a direct integration of the Poisson equation. The results of the method are compared to those given by a one-dimensional model. It is then applied to get some information which is useful in the theory of near field microscopy: Curvature of the energy bands at the semiconductor surface, influence of the tip shape, range of the electric field, effect of a dielectric insulating layer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366419
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic structure and optical properties of silicon crystallites: Application to porous silicon (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1948-1950 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have calculated the electronic structure of spherical silicon crystallites containing up to 2058 Si atoms. We predict a variation of the optical band gap with respect to the size of the crystallites in very good agreement with available experimental results. We also calculate the electron-hole recombination time which is of the order of 10−4–10−6 s for crystallites with diameters of 2.0–3.0 nm. We conclude that small silicon crystallites can have interesting optical properties in the visible range. These results are applied to porous silicon for which we confirm that a possible origin of the luminescence is the quantum confinement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108372
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum confinement in amorphous silicon layers (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1189-1191 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic structure of hydrogenated amorphous silicon layers is calculated within the empirical tight binding approximation. We predict an important blueshift due to the confinement for layer thickness below 3 nm, and we compare with crystalline silicon layers. The radiative recombination rate is enhanced by the disorder and the confinement but remains much weaker than that in direct band gap semiconductors. The comparison of our results with experimental data shows that the density of defects and localized states in the studied samples is quite small. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119621
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of barrier height on scanning tunneling spectroscopy experimental and theoretical aspects (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 569-571 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning tunneling spectroscopy allows the determination of the density of states of the involved electrodes as well as the associated barrier height. We have measured the barrier height between tungsten tip and the GaAs (110) surface with a scanning tunneling microscope (STM) in ultrahigh vacuum. When the tunneling junction exhibited a low barrier height, we observed and explained an apparent widening of the GaAs gap which can mislead the real doping concentration of the sample. A theoretical model based on the self-consistent Keldysh–Green functions formalism is used to calculate the STM current. It shows a possible lowering of the barrier height according to the adsorption of As or Ga atoms on the apex of the tungsten tip. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120762
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum confinement in the Si-III (BC-8) phase of porous silicon (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2437-2439 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Porous silicon was recently shown to give rise to the same semimetallic Si-III (BC-8) phase as silicon upon application and release of high pressure. This phase is known to have a direct gap and we examine the effect of quantum confinement on its electronic structure. This is performed by combining empirical tight binding and ab initio local density calculations. The blue shift is found to be similar to what is obtained for nanocrystallites with the diamond structure and the radiative recombination rate is much larger. Comparison with experiment shows that the observed luminescence is not consistent with the quantum confinement hypothesis. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118895
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  • 6
    Electronic Resource
    Electronic Resource
    Quantum confinement in germanium nanocrystals (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1182-1184 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic structure of Ge nanocrystals is studied using a sp3 tight binding description. Analytical laws for the confinement energies, valid over the whole range of sizes, are derived. We validate our results with ab initio calculations in the local density approximation for smaller clusters. Comparing to experimental data, we conclude that, similar to the case of silicon: (a) the blue-green photoluminescence (PL) of Ge nanocrystals comes from defects in the oxide and (b) the size dependent PL in the near infrared probably involves a deep trap in the gap of the nanocrystals. We predict that the radiative lifetimes remain long in spite of the small difference (0.14 eV) between direct and indirect gaps of bulk Ge. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289659
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  • 7
    Electronic Resource
    Electronic Resource
    Defect-assisted tunneling current: A revised interpretation of scanning tunneling spectroscopy measurements (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3142-3144 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scanning tunneling microscopy (STM) is used to study low temperature grown GaAs layers. Excess As gives rise to a high concentration of As antisites (AsGa). On these point defects, tunneling spectroscopy reveals a band of donor states. In fact, the measured tunneling current results from a pure tunneling current between the energy levels of the STM tip and the AsGa energy level Et followed by an exchange of carriers between Et and the bands or between Et and donor states of neighbor point defects. We determine the influence of both contributions on the current. We show that hopping conduction is required to explain the observation of the midgap states in tunneling spectroscopy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126550
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  • 8
    Electronic Resource
    Electronic Resource
    Quantum confinement energies in zinc-blende III–V and group IV semiconductors (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 639-641 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Blueshift of the band gap due to quantum confinement is calculated in a tight-binding model for a series of nine III–V zinc-blende AB (A=Al, Ga, or In, B=As, P, or Sb) and two diamond group-IV (Si and Ge) semiconductor clusters. Analytic expressions for the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are given as a function of the cluster size. Comparison is made to results obtained by the pseudopotential method and to experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.127070
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  • 9
    Electronic Resource
    Electronic Resource
    Atomic-scale study of GaMnAs/GaAs layers (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4001-4003 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cross-sectional scanning tunneling microscopy was used to study GaMnAs diluted magnetic semiconductors grown by low temperature molecular beam epitaxy. The Ga1−xMnxAs layer, containing a concentration of x=0.005, shows that the dominant defect in the material is the arsenic antisite. Mn ions can also be resolved and show a signature distinct from the arsenic antisites. Spectroscopic measurements are perfomed to study the variation of the Fermi level between the Ga0.995Mn0.005As and GaAs layers. The Mn ions act as acceptor dopants. However, for x=0.005, the Mn concentration in comparison with the As antisite concentration is too small to induce a significant change of the Fermi level from the midgap position, preventing the layer from being ferromagnetic. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1322052
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  • 10
    Electronic Resource
    Electronic Resource
    Theoretical characterization of the electronic properties of extended thienylenevinylene oligomers (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6643-6649 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present semiempirical tight binding calculations on thienylenevinylene oligomers up to the hexadecamer stage (n=16) and ab initio calculations based on the local density approximation up to n=8. The results correctly describe the experimental variations of the gap versus size, the optical spectra, and the electrochemical redox potentials. We propose a simple model to deduce from the band structure of the polymer chain the electronic states of the oligomers close to the gap. We analyze the evolution of the gap as a function of the torsion angle between consecutive cells: the modifications are found to be small up to a ∼30° angle. We show that these oligomers possess extensive π-electron delocalization along the molecular backbone which makes them interesting for future electronic applications such as molecular wires. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480012
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