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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Correlation of substitutional hydrogen to refractive index profiles in annealed proton-exchanged Z- and X-cut LiNbO3 (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2697-2708 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Previous disagreements concerning a linear correlation between the hydrogen (H) concentration and the extraordinary refractive index ne in proton-exchanged lithium niobate (LiNbO3) have been resolved by partitioning the total H into optically active substitutional H and optically inactive interstitial H. The H and Li spatial variations in both Z- and X-cut crystals were determined by secondary-ion-mass spectrometry (SIMS) with a quantitative evaluation in atoms/cm3. These samples were proton exchanged in neat benzoic acid at 185 °C and then were annealed at 400 °C for times t from 6 to 240 min in wet flowing oxygen. For the Z-cut crystals, fit of the SIMS measured H profiles by expressions obtained from the diffusion equation for diffusion from a finite layer gave a substitutional H diffusivity of DZs=5.0±0.3×10−12 cm2/s and an interstitial H diffusivity of DZi=1.4±0.1×10−11 cm2/s. The wet flowing oxygen acts as a constant source of interstitial H at the surface with the diffusivity DZi and gives an integrated H concentration due to the flowing wet oxygen which increases as (square root of)t. The Li diffusivity was DLiZ=4.8±0.2×10−12 cm2/s which is nearly equal to DZs. For X-cut crystals, the substitutional H diffusivity was DXs=3.4±0.2×10−12 cm2/s and the interstitial diffusivity was DXi=1.3±0.2×10−11 cm2/s. The ne profiles were evaluated by means of optical prism-coupling measurements and numerical simulations. In both cases of crystal orientation, the effective index diffusivity is nearly equal to the diffusivity of substitutional H. Furthermore, there is an excellent linear relationship between the ne profile and the corresponding substitutional H distribution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358738
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Secondary ion mass spectrometry depth profiling of proton-exchanged LiNbO3 waveguides (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 6055-6058 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Simultaneous depth profiles for H and Li have been measured in proton-exchanged lithium niobate crystals (LiNbO3) by the use of charge-compensated secondary ion mass spectrometry (SIMS). Electron flooding of the insulator during sputtering permits accurate depth profiling through the exchanged region and into the substrate. Four samples of z-cut proton-exchanged LiNbO3 were analyzed using SIMS, and were used in optical waveguiding experiments. In each sample, the H distribution is in the shape of a plateau that extends from the surface to a depth that is in good agreement with the results of the optical waveguiding measurements.The Li profiles show reduced concentrations within the regions of high H concentration, that is, within the waveguiding regions. Based on SIMS data, the proton-exchange process appears to stabilize at a value of 0.4〈x〈0.5 for the Li1−xHxNbO3 compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343584
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  • 5
    Electronic Resource
    Electronic Resource
    A study of proton exchange in congruent single-crystal LiNbO3 by atomic absorption spectroscopy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3968-3970 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Atomic absorption spectroscopy has been used to determine Li+ concentrations in benzoic acid after proton exchange with x- and z-cut LiNbO3 as a function of exchange time and temperature. The atomic absorption results, in agreement with our previous infrared spectroscopic and optical waveguide measurements, indicate that there is no evidence for saturation of the melt by Li+ at typical melt volumes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345007
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of waveguides formed by proton-exchange in MgO-doped and Nd:MgO-doped LiNbO3: A comparison with congruent material (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3964-3967 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Proton-exchanged waveguides fabricated in LiNbO3 doped with 4.5% MgO and 0.1–0.2 % Nd:4.5% MgO have been characterized by prism-coupling and infrared-absorption spectroscopy. Single and multimode doped waveguides have temporally stable effective mode indices, and the refractive-index profiles are identical to those observed for proton exchange in congruent LiNbO3. Effective diffusion coefficients for proton exchange in doped x and z-cut substrates have been estimated for waveguide-fabrication temperatures in the range 182–235 °C. While diffusion coefficients for MgO:LiNbO3 and Nd:MgO:LiNbO3 appear to be identical, waveguides formed in the doped substrates have substantially smaller diffusion coefficients compared to waveguides formed in congruent LiNbO3, the magnitudes being down by as much as 50% for x-cut waveguides and 37% for z-cut waveguides. These results should prove of value when using the proton-exchange technique to design waveguide lasers in Nd:MgO:LiNbO3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345006
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Proton-exchanged, lithium niobate planar-optical waveguides: Chemical and optical properties and room-temperature hydrogen isotopic exchange reactions (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 64-67 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Planar-optical waveguides fabricated by [1H] and [2H] hydrogen exchange on x- and z-cut lithium niobate are compared with respect to their behavior towards atmospheric [2H] and [1H] water vapor and their optical properties. The extent of [1H]–[2H] hydrogen isotopic exchange was monitored by infrared spectroscopy in the hydroxyl-group stretching region. We show that [1H]- and [2H]-exchange waveguide materials behave differently and therefore cannot be regarded as structurally identical. However, optical mode-angle measurements using prism coupling have established that the waveguide profiles in these materials are almost identical in form, and can be modeled accurately by a step-index change with Δne (approximately-equal-to)0.12 at λ=0.6328 μm. Lithium present in molten benzoic acid after its reaction with z-cut LiNbO3 samples has been determined by atomic absorption spectroscopy. The lithium concentration data obtained are in satisfactory agreement with previous estimates of hydrogen concentrations in the exchanged waveguide layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338801
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  • 9
    Electronic Resource
    Electronic Resource
    Correlation of refractive index profiles with substitutional hydrogen concentrations in annealed proton-exchanged LiNbO3 waveguides (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2769-2771 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the behavior of the extraordinary refractive index in a set of annealed z-cut proton-exchanged lithium niobate (LiNbO3) substrates by means of optical prism-coupling measurements and numerical simulations. Values of the index as a function of depth have been determined and fitted with a single Gaussian diffusion expression. At 400 °C, the effective index diffusivity Dn of 4.6×10−12 cm−2/s is nearly identical to the diffusivity of substitutional H in these samples. Furthermore, we find a linear relationship between the increase in the extraordinary refractive index and the substitutional H concentration. At a wavelength of 0.6238 μm, the coefficient for this relationship is ∼1.5×10−23 (H cm−3)−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109255
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  • 10
    Electronic Resource
    Electronic Resource
    Relationship between storage media and blue photoluminescence for oxidized porous silicon (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 107-109 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Blue photoluminescence is observed, with nanosecond decay time, from rapid thermally oxidized porous silicon as a result of accelerated aging in plastic containers. Photoluminescence measurements, combined with chemical analyses of the "aged" porous silicon, indicate that the emission is a consequence of the incorporation of trace organic (hydrocarbon) contamination from the plastic containers as they outgas at a mildly elevated temperature (80 °C) and, albeit at a reduced rate, at room temperature. Such carbonaceous contaminants can subsequently be removed by high-temperature annealing, a process which also quenches the blue photoluminescence. Consequently, it is important to take into consideration the storage medium used when making comparative luminescent and compositional studies of porous silicon and, perhaps, porous materials in general. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119442
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