Showing papers by "Paulo V. Santos published in 1999"
TL;DR: In this article, the authors investigated the dynamics of the crystallization process by two-dimensional finite element computer simulations of the heat transport and phase transitions during laser crystallization of polycrystalline silicon lines with lateral dimensions between 0.5 and 20 μm.
Abstract: Laser interference crystallization of amorphous silicon (a-Si) thin films, a technique that combines pulsed laser crystallization with holography, enables the fabrication of periodic arrays of polycrystalline silicon (poly-Si) lines with lateral dimensions between 0.5 and 20 μm. The lines consist of grains with well-defined grain boundary locations and lateral dimensions that are appreciably larger than the thickness of the initial a-Si:H film (up to 2 μm for a 300 nm thick film). We investigated the dynamics of the crystallization process by two-dimensional finite element computer simulations of the heat transport and phase transitions during laser crystallization. The theoretical results were compared to: (i) measurements of the crystallization kinetics, determined by recording the transient changes of the reflectance during laser exposure, and to (ii) the structural properties of the crystallized films, determined by scanning force and transmission electron microscopy. The simulations indicate that the...
35 citations
TL;DR: Reflectance difference spectroscopy (RDS) has been used to determine piezo-optical coefficients of semiconductors above the fundamental gap as mentioned in this paper, which allows the determination of these coefficients with the use of very small uniaxial stresses (<0.05 GPa).
Abstract: Reflectance difference spectroscopy (RDS) has been used to determine piezo-optical coefficients of semiconductors above the fundamental gap. The high sensitivity of the RDS technique allows the determination of these coefficients with the use of very small uniaxial stresses (<0.05 GPa). By measurement of RDS on samples of cubic crystals under uniaxial stress along the [001] and [111] crystal directions, the piezo-optical coefficients P11-P12 and P44, respectively, were determined. Measurements on InP give results in good agreement with previously reported values obtained by ellipsometry. RDS was used successfully to determine the spectral dependence of P11-P12 in ZnSe, a II–VI semiconductor too brittle to support the stresses required for ellipsometric measurements. RDS is less sensitive than ellipsometry to the presence of surface overlayers.
17 citations
TL;DR: In this paper, the mapping of surface acoustic wave (SAW) fields by means of microscopic reflectance and reflectance anisotropy in GaAs-based structures is reported.
Abstract: The mapping of surface acoustic wave (SAW) fields by means of microscopic reflectance and reflectance anisotropy in GaAs-based structures is reported. The two techniques are complementary with the second being sensitive to the strain and the first both to the strain and to the surface modulation induced by the SAW. Their combination provides information about both the longitudinal and transverse components of the SAW particle displacement vector.
17 citations
6 citations
TL;DR: In this paper, the polarization anisotropy of the photoluminescence from quasiplanar quantum wires fabricated on the sidewall of [011]-oriented mesas on the (311)A GaAs surface is investigated using a modulation technique that combines high spatial (∼1 μm) and polarization resolution (<0.1%).
Abstract: The polarization anisotropy of the photoluminescence from quasiplanar quantum wires fabricated on the sidewall of [011]-oriented mesas on the (311)A GaAs surface is investigated using a modulation technique that combines high spatial (∼1 μm) and polarization resolution (<0.1%). Due to their low symmetry, (311)A-oriented quantum wells are intrinsically anisotropic with the fundamental transition preferentially oriented along the [233] direction. The anisotropy contribution from the lateral confinement in the [011] wires opposes that from the vertical confinement. With increasing lateral confinement, the wire anisotropy initially reduces and then changes its sign. The lateral extent of the electronic wave functions involved in the anisotropic transitions is obtained from a comparison of the results with a theoretical model.
3 citations
TL;DR: In this paper, the polarization anisotropy of the excitonic photoluminescence (PL) of quantum wells (QWs) and of [0-11]-oriented sidewall quantum wires (QWRs) grown on (311) GaAs substrates was investigated.
Abstract: We investigate the polarization anisotropy of the excitonic photoluminescence (PL) of quantum wells (QWs) and of [0-11]-oriented sidewall quantum wires (QWRs) grown on (311) GaAs substrates. We demonstrate that vertical (i.e., along [311]) and lateral (along [-233]) confinements in these QWRs yield contributions of opposite signs to the PL anisotropy. The anisotropy of the QWRs initially reduces and then changes sign with decreasing wire widths.
2 citations
TL;DR: In this paper, the interaction between a surface acoustic wave (SAW) and photogenerated carriers in GaAs/Al 0.3 Ga 0.7 As quantum well (QW) structures is investigated using micro-photoluminescence (μ-PL).
Abstract: The interaction between a surface acoustic wave (SAW) and photogenerated carriers in GaAs/ Al 0.3 Ga 0.7 As quantum well (QW) structures is investigated using micro-photoluminescence (μ-PL). The excitonic luminescence becomes strongly suppressed in the presence of a SAW due to the ionization of the excitons and to the transport of the photogenerated carriers by the piezoelectric field. We demonstrate that the degree of μ-PL quenching and the carrier transport efficiency depends not only on the intensity of the piezoclectric field but also on the carrier mobility in the QW.
2 citations
1 citations