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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of microporous Si by flow calorimetry: Comparison with a hydrophobic SiO2 molecular sieve (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1558-1565 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flow microcalorimetry has been used to study microporous silicon produced by electrochemical corrosion of bulk p-type silicon wafers in highly concentrated (50 wt %) aqueous hydrofluoric acid. Calorimetry data on pore size and hydrophobicity of freshly etched crystalline silicon structures are compared with similar measurements on silicalite, a well-studied microporous form of crystalline silicon dioxide. Silicalite has a tetrahedral SiO2 framework with interconnected "ultramicropores'' that only readily admit molecules of less than 6 A(ring) diameter. Its measured heat of immersion in n-heptane (kinetic diameter 4.3 A(ring)) consequently far exceeds that in iso-octane (kinetic diameter 6.2 A(ring)) and it preferentially adsorbs the normal alkane from the branched alkane. In direct contrast the microporous Si layers studied exhibited comparable heats of immersion for n-heptane and iso-octane, and did not show any preferential adsorption of the narrower molecule. In addition, the microporous Si layers studied exhibited appreciable heats of immersion in 1, 3, 5 tri-isopropylbenzene (kinetic diameter 8.5 A(ring)). The majority of their pore volume is thus constrained to the "supermicropore'' size regime of 10–20 A(ring) width. Both silicalite and freshly etched microporous Si are shown, however, to be highly hydrophobic and organophilic materials. Their exothermic heats of immersion in n-heptane far exceed those in water and both materials preferentially interact with the polar alcohol (n-butanol) more strongly from water than from n-heptane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351725
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  • 2
    Electronic Resource
    Electronic Resource
    Correlation of the structural and optical properties of luminescent, highly oxidized porous silicon (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 493-501 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The light-emitting properties of rapid thermally oxidized porous Si are studied by both photoluminescence and cathodoluminescence methods. The structure of the material is examined by transmission electron microscopy, while its oxygen content is determined by x-ray microanalysis. These investigations show that crystalline Si nanostructures remain in the heavily oxidized porous material and account for its ∼750 nm red photo- and cathodoluminescence. The work demonstrates that the previously speculated possible importance of either Si-based amorphous phases or the interesting material, siloxene, in this regard is unrealistic. Furthermore, it is shown that the luminescence properties of silicon oxides are of paramount importance in interpreting the many additional (shorter wavelength) emission bands observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355827
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  • 3
    Electronic Resource
    Electronic Resource
    1.3-μm light-emitting diode from silicon electron irradiated at its damage threshold (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1509-1511 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report 77-K electroluminescence from an irradiated carbon-rich silicon diode that has an internal quantum efficiency more than 103 times higher than that of band-to-band recombination in an unirradiated, but otherwise identical diode. This is achieved by creating optically active Cs-SiI-Cs complexes with room-temperature electron bombardment at an energy between the displacement thresholds for single vacancy and divacancy formation. Under these irradiation conditions, it is possible to create a high concentration of radiative defects without gross degradation of the diode's electrical characteristics. The technique could provide very large scale integration-compatible silicon light-emitting diodes for 1.3–1.6 μm all-silicon integrated optics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98618
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  • 4
    Electronic Resource
    Electronic Resource
    Blue photoluminescence from rapid thermally oxidized porous silicon following storage in ambient air (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3557-3559 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the temporal variation of the visible photoluminescence from rapid thermally oxidized porous silicon prepared from n+ substrates. In contrast to the red (slow band) emission, which is observable immediately after high-temperature oxidation, the blue (fast band) emission is shown to become prevalent only after samples are stored in ambient air. The intensity of the blue emission increases with progressive aging, the magnitude of the increase being dependent on the temperature at which the material is oxidized. Thermal treatment of aged rapid thermally oxidized material can reduce and even quench the blue photoluminescence. Quenching is reversible in that the photoluminescence re-appears after further aging at room temperature. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358587
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  • 5
    Electronic Resource
    Electronic Resource
    Compositional variations of porous silicon layers prior to and during ion-beam analyses (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2825-2832 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The suitability of ion-beam-analysis techniques in quantifying the composition of mesoporous silicon nanostructures has been critically examined using films of moderate porosity (55%) prepared on n+ substrates. The effects of room-temperature aging of as-etched and thermally oxidized porous silicon, the oxidation conditions chosen to render the material luminescent, have been carefully monitored, as have the effects of both ion-beam irradiation and storage of samples in vacuo. It is shown that the concentrations of the three major impurities oxygen, carbon, and hydrogen can be appreciably altered during analyses, thereby limiting the reliability of the techniques, as conventionally applied to porous silicon. The use of appropriate capping layers, which should alleviate the problem, is recommended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357517
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  • 6
    Electronic Resource
    Electronic Resource
    Surface copper contamination of as-received float-zone silicon wafers (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 920-927 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As-received float-zone Si wafers from two major suppliers are shown to have surface Cu contamination at a level of ∼5×1011 atoms cm−2, detectable by both low-temperature photoluminescence and room-temperature x-ray fluorescence. The effects of selective chemical removal of Cu from, or Cu adsorption onto, the front or rear surfaces of wafers have demonstrated where the majority of the contamination resides, thereby revealing its possible origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343521
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  • 7
    Electronic Resource
    Electronic Resource
    Near-band-gap photoluminescence from pseudomorphic Si1−xGex single layers on silicon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1407-1414 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The systematic study of band-edge luminescence in pseudomorphic Si/Si1−xGex/Si double-heterostructure layers is reported for a wide composition range, 0.12〈x〈0.24, for the first time. An analytical expression for the exciton energy gap at 4.2 K valid for x〈0.24 is derived from the no-phonon line energies: ESX(x) = 1.155−0.874x+0.376x2 eV. Addition of an expression for the exciton binding energy provides an approximation for the energy difference between the alloy valence band and the lowest conduction-band edge at low temperature. An exciton upshift of 16.9 meV due to quantum confinement is observed in a 6.3-nm Si0.83Ge0.17 alloy well. This is consistent with either type-I or type-II band alignment for which the conduction-band offset has a magnitude ||ΔEc|| ≤ 10 meV. The excitonic hole is closely confined in the alloy but the spectra suggest that the electron density in the silicon barriers is increased for the thin layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351262
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  • 8
    Electronic Resource
    Electronic Resource
    Atmospheric impregnation of porous silicon at room temperature (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 422-431 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microporous and mesoporous Si layers contain a very large surface area that affects both their optical and electrical properties. Secondary ion mass spectroscopy (SIMS) analysis is used for the first time to simultaneously monitor all the major impurities on that surface. SIMS data on a microporous layer demonstrate that its chemical composition changes dramatically with time during ambient air exposure. Similar trends are observed for mesoporous layers. Extended storage in air at room temperature converts the hydride surface of freshly anodized layers to that of a contaminated native oxide. Characterization techniques need to take the metastability of the hydride surface into account since the structural, optical, and electrical properties of porous Si can consequently change with time upon exposure to ambient air. Low-temperature photoluminescence and spectroscopic ellipsometry data on freshly anodized and "aged'' microporous and mesoporous layers are chosen to illustrate typical changes in optical properties and the timescales involved. Spreading resistance analysis is also shown for the first time to provide depth information on the resistivities of porous layers and their variation with extended exposure to air. Implications for other characterization techniques are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350293
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  • 9
    Electronic Resource
    Electronic Resource
    Modulation speed of an efficient porous silicon light emitting device (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2764-2773 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Trends in the efficiency and small signal modulation behavior of porous silicon light emitting diodes (LEDs) are reported for devices formed by the anodization of bulk silicon p–n junctions. As the average size of the silicon skeleton is decreased, the external electroluminescence (EL) efficiency increases from 0.001% to 0.18% and there is a corresponding blue shift in the EL peak from 776 to 633 nm. An associated tenfold increase is observed in the photoluminescence efficiency while the diode resistance, at 2 V, increases from 3×103 to 1×106 Ω. Under small signal pulsed operation, the voltage dependence of the rising edge of the EL is well described by a carrier mobility of 3×10−4 cm2 s−1 V−1 which is independent of the average size of the luminescent regions of the silicon nanostructure. The falling edge of the EL transient is dominated by radiative recombination of quantum confined excitons. The modulation speed is found to be limited by a combination of carrier mobility in the silicon wires and radiative recombination processes. Evidence of charge trapping and discharge is found in an EL overshoot phenomenon. The major application of this type of porous silicon LED, with modulation speeds below 1 MHz, appears to be for displays integrated with circuitry rather than for optical interconnection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371123
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  • 10
    Electronic Resource
    Electronic Resource
    Efficient visible electroluminescence from highly porous silicon under cathodic bias (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2563-2565 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Visible electroluminescence (EL) has been obtained from porous silicon cathodically biased in an aqueous electrolyte containing either the persulphate or the peroxide ion. EL efficiencies of up to 0.1% have been obtained from porous silicon formed on both n-type and p-type substrates for the application of only a few volts bias. In subdued lighting, the EL is easily visible to the naked eye at excitation densities of 0.1 W cm−2. EL is obtained only from porous silicon capable of giving photoluminescence (PL); the EL and PL spectra are broadly similar in width and peak wavelength. The EL spectra are reversibly shifted to shorter wavelengths as the magnitude of the bias is increased. In contrast with the previously reported EL under anodic conditions, this cathodic EL process does not irreversibly oxidize the porous silicon skeleton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108127
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