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  • 1
    Digitale Medien
    Digitale Medien
    Photo-assisted tuning of luminescence from porous silicon (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6365-6367 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A method is proposed to control the wavelength of visible photoluminescence (PL) from porous silicon (PS). This is based on the post-anodization illumination technique which employs a filtered light with various maximum cutoff photon energies. As the illumination time increases, the PL spectra shift toward the higher energy side. This blue shift tends to stop at the time when the PL peak energy becomes close to the cutoff photon energy. The emission wavelength can be controllably tuned in a wide spectral range by changing the cutoff filter. These results give us a strong indication that the visible PL of PS is closely related to interband excitation in Si nanocrystallites, not to some surface chemical compounds.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355160
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  • 2
    Digitale Medien
    Digitale Medien
    Laser-induced thermal effects on the optical properties of free-standing porous silicon films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 1788-1794 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A detailed study of the unique optical properties of free-standing oxidized porous silicon films has been performed. Under continuous-wave laser irradiation, a strongly superlinear light emission and a very large laser-induced absorption are observed. The nonlinear emission is characterized by a sharp intensity increase that is in proportion to at least the eighth power of the excitation intensity. This emission has a broad peak (600–1300 nm), slow time constant (≥10 ms), and very low polarization memory (≤0.01 near the emission peak). The induced absorption increases linearly with the pump laser intensity and can be as large as several times the linear absorption. The increase in the normalized absorption coefficient is almost independent of the oxidation temperature and emission wavelength, with essentially no polarization dependence. These experimental results are discussed in terms of laser-induced thermal effects. An evaluation of the temperature rise under the laser irradiation is performed both experimentally and theoretically. A remarkably high-temperature rise of ≥700 °C is estimated for a moderate excitation intensity of 20 W/cm2. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372093
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  • 3
    Digitale Medien
    Digitale Medien
    Mechanism of the visible electroluminescence from metal/porous silicon/n-Si devices (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 1407-1412 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The excitation and radiative recombination mechanisms of carriers in electroluminescent porous silicon (PS) have been studied for the device with the structure of Au/PS/n-type Si. Experiments focus on the electroluminescence (EL) and photoluminescence (PL) spectra, the current-voltage-EL intensity relationship and its temperature dependence, and the excitation-wavelength dependence of the electric-field-induced PL quenching. The results of these experiments suggest the following points: (1) the EL occurs mainly near the Au/PS contact; (2) there exists an extremely high electric field at the Au/PS contact; (3) the EL originates from radiative recombination of strongly localized excitons; and (4) the radiative recombination rate is in proportion to the diode current. Based on these observations, an operation model is proposed. In our model, a large number of electrons and holes are generated in the PS layer by a field-assisted mechanism. Light emission occurs by radiative recombination of these electrons and holes via localized states. Because of field-enhanced carrier separation, however, the EL efficiency of this device is limited to a relatively low value of about 0.05%. Possible ways to improve the EL characteristics are discussed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363878
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  • 4
    Digitale Medien
    Digitale Medien
    Photoelectronic properties of porous silicon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1986-1988 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is shown that the introduction of a porous structure into single-crystal Si produces substantial changes in the photoelectronic properties. The porous Si (PS) layer is formed by anodization of p-type Si wafers in a HF solution. The photoconduction cells used in this study consists of a semitransparent thin Au film, PS, Si substrate, and Al ohmic contact. The photoconductive behavior of PS is characterized by an extremely high dark resistivity, a definite photosensitivity for visible light, and an intrinsic bias voltage dependence of the spectral response. These properties, which are interpreted to be the result of a band-gap widening in PS, provide further support of the assumption that the visible luminescence of PS is explained by the band scheme.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357663
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  • 5
    Digitale Medien
    Digitale Medien
    Precisely tuned emission from porous silicon vertical optical cavity in the visible region (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4841-4844 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The operating peak energy of a porous silicon (PS) cavity can be completely controlled over a wide range of 1.5–2.2 eV, using a PS-based Fabry–Perot resonator composed of a light-emitting active PS layer and two high-reflectivity mirrors. When the PS devices are excited by a uv laser, quite narrow spectra (10–40 meV in full width at half-maximum) are observed without any significant signs of side mode. The central photon energy is precisely and continuously tuned simply by changing the anodization parameters. The key issues of the controlled device operation are adjustment of the optical thickness of the active PS layer to an appropriate value and fabrication of the quarter-wavelength multilayered PS mirror with a high reflectivity. The spectral qualities of the emitted light are also discussed by theoretical analyses on the basis of a simplified model. These results suggest that the PS devices operate as sharp band-pass optical filter and the PS materials are available for novel silicon-based microphotonics. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363526
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  • 6
    Digitale Medien
    Digitale Medien
    Activation of blue emission from oxidized porous silicon by annealing in water vapor (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1776-1778 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is reported that annealing of oxidized porous silicon in water vapor at about 250 °C drastically enhances its blue emission. Infrared absorption studies indicate that this annealing increases all the absorption peaks related to O–H vibrations, except for that of free silanol which disappears completely. No traces of carbon-related signals are observed. The latter result makes a clear objection to blue-band luminescence models based on adsorbed carbon compounds. Although the possibility of silanol-related origins cannot be ruled out, we suggest that some passivation effect of adsorbed hydroxyls on Si nanostructures surrounded by SiO2 is also likely. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.366899
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  • 7
    Digitale Medien
    Digitale Medien
    Electrical quenching of photoluminescence from porous silicon (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3177-3179 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have studied the visible photoluminescence (PL) of porous silicon (PS) under the condition that a bias voltage is applied in the direction of the PS layer thickness. It is shown, for the first time, that the PL intensity is sharply decreased when increasing the voltage. This electrical PL quenching was completely reversible. This phenomenon is interpreted as to arise from field-enhanced tunneling of carriers between silicon crystallites. The result presented here strongly suggests that the visible luminescence of PS is not based on electronic transitions in some molecular substance, but on the radiative recombination in Si nanocrystallites.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109121
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  • 8
    Digitale Medien
    Digitale Medien
    Optical characterization of porous silicon by synchrotron radiation reflectance spectra analyses (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2774-2776 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electronic structure of porous Si(PS) has been characterized by optical reflectance spectra analyses. The reflectance spectra of PS were measured in the photon energy range of 2–27 eV using a synchrotron radiation source. The reflectance at the low energy region was calibrated by the corresponding absolute value which was separately determined from spectroscopic ellipsometry. The spectral response of optical constants were calculated by the Kramers–Kronig analysis. Our results indicate that PS retains some of the characteristic optical features of crystalline Si, and that a blue shift in the absorption edge occurs in PS.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.110330
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  • 9
    Digitale Medien
    Digitale Medien
    Visible electroluminescence from porous silicon (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 347-349 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is demonstrated that photoluminescent porous Si (PS) layers exhibit definitely visible electroluminescence (EL). The PS layers were formed by anodization of single-crystal nondegenerate p-type Si wafers in an HF solution. The experimental EL cells are of the form semitransparent metal/PS layer/p-type Si/Al electrode. These cells show a rectifying junction behavior. When the forward current density reaches a certain value, stable visible (orange) light is uniformly emitted through a semitransparent electrode. A possible explanation of this is the radiative transition due to electron and hole injection into quantized states in PS.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.106652
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  • 10
    Digitale Medien
    Digitale Medien
    Post-anodization filtered illumination of porous silicon in HF solutions: An effective method to improve luminescence properties (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1656-1658 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A useful method is presented to improve the luminescence efficiency of porous silicon (PS) based on the post-anodization illumination of samples in HF solutions. In the present method the illumination is performed by a white lamp through sharp-cut long-wavelength-pass filters to remove the short wavelength component from the illumination light. The PS samples prepared by this method exhibited the visible photoluminescence (PL) with an efficiency of one order of magnitude higher than those illuminated without filters. The efficiency improvement is attributed to the reduction of the deteriorative surface oxidation of Si crystallites in PS. The filtered illumination technique is also useful to produce a larger PL blue shift and precise control of PL spectra.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112946
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