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  • 1
    Electronic Resource
    Electronic Resource
    Direct measurement of the deep defect density in thin amorphous silicon films with the "absolute'' constant photocurrent method (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6203-6210 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct measurement of the deep defect density in thin amorphous silicon films with the help of the "absolute'' constant photocurrent method is demonstrated here. We describe in detail how the optical (photocurrent) absorption spectrum can be measured directly in absolute units (cm−1) without additional calibration and undisturbed by interference fringes. Computer simulation was performed to demonstrate absolute precision of the measurement and to explain residual interferences which are sometimes observed. The residual interferences are shown to be direct fingerprints of an inhomogeneous defect distribution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360566
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  • 2
    Electronic Resource
    Electronic Resource
    Carrier diffusion in porous silicon studied by transient laser-induced grating spectroscopy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2481-2486 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report laser-induced transient grating experiments performed at room temperature on self-supporting p-type porous silicon films with different porosities. With this technique the diffusion of the photocarriers can be studied with a time resolution of some tens of picoseconds. The gratings were created by two interfering pulses of the second-harmonic radiation from an Nd3+:yttrium-aluminum-garnet YAG laser (2.3 eV) and their decay in time was studied by a time-delayed pulse of the fundamental YAG laser frequency (1.15 eV). The observed grating decay time is very fast (hundreds of picoseconds) and shortens with decreasing porosity. Diffusion constants D=45, 24, and 5 cm2 s−1 have been found for the porosities of 64%, 68%, and 73%, respectively. To explain these high values of D we consider a simple kinetic model which takes into account two different types of carriers, delocalized and trapped ones. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361177
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  • 3
    Electronic Resource
    Electronic Resource
    Transport anisotropy in microcrystalline silicon studied by measurement of ambipolar diffusion length (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1800-1805 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied charge transport anisotropy in microcrystalline silicon (μc-Si:H) by comparing diffusion length measured parallel to the substrate by steady stage photocarrier grating and perpendicular to the substrate by surface photovoltage method (SPV). We have developed a SPV evaluation procedure which allowed us to exclude the effect of light scattering at the naturally rough surface of the μc-Si:H. The procedure allows us to deduce not only the diffusion length, but also the depth of the depletion layer at the surface and recombination coefficients at both top and bottom interfaces of the film. With growing μc-Si:H film thickness the size of the crystallites increases, leading to higher roughness and thus also light scattering. At the same time density of grain boundaries decreases, resulting in an increase of the diffusion length and of the surface depletion layer depth. For all samples the diffusion length perpendicular to the substrate was several times higher than the diffusion length parallel to it, clearly confirming previous indication of the transport anisotropy resulting from the measurements of coplanar and sandwich conductivity. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1338996
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  • 4
    Electronic Resource
    Electronic Resource
    Optical absorption and light scattering in microcrystalline silicon thin films and solar cells (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 148-160 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical characterization methods were applied to a series of microcrystalline silicon thin films and solar cells deposited by the very high frequency glow discharge technique. Bulk and surface light scattering effects were analyzed. A detailed theory for evaluation of the optical absorption coefficient α from transmittance, reflectance and absorptance (with the help of constant photocurrent method) measurements in a broad spectral region is presented for the case of surface and bulk light scattering. The spectral dependence of α is interpreted in terms of defect density, disorder, crystalline/amorphous fraction and material morphology. The enhanced light absorption in microcrystalline silicon films and solar cells is mainly due to a longer optical path as the result of an efficient diffuse light scattering at the textured film surface. This light scattering effect is a key characteristic of efficient thin-film-silicon solar cells. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373635
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  • 5
    Electronic Resource
    Electronic Resource
    Amorphous/microcrystalline silicon superlattices—the chance to control isotropy and other transport properties (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2540-2542 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Preparation of amorphous silicon/microcrystalline silicon superlattices allowed us a systematic study of transition from isotropic amorphous silicon to microcrystalline silicon with anisotropic (columnar) microstructure. The fact that just a few nm of amorphous interlayers are sufficient to interrupt columnar growth of crystallites is reflected in a clearly demonstrated isotropy of transport properties of all superlattice samples. Values of dark conductivity and diffusion length as well as grain size vary with changing crystallinity and so we can tailor the properties of the resulting material by adjusting thicknesses of amorphous and microcrystalline layers repeated to achieve a total desired thickness. Properly selected design of superlattice can lead to transport properties more suitable for solar cells than with pure microcrystalline silicon. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410364
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  • 6
    Electronic Resource
    Electronic Resource
    Instabilities in electroluminescent porous silicon diodes (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 833-835 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of high quantum efficiency, porous silicon (PS) electroluminescent (EL) diodes have been analyzed under pulsed operation. The results show that EL exhausting is due to a charging of the PS network which recovery is thermally activated (Er∼0.4 eV). This suggests a charge trapping mechanism at larger crystallites with low bandgap, inhibiting further injection of carriers. Also, forward current is found to be thermally activated, however, with a distinctly lower activation energy (Ej∼0.1–0.2 eV), possibly related to jumping of carriers over barriers between nearby crystallites. Finally, high current densities may lead to thermal runaway causing permanent damage to the structure. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117907
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  • 7
    Electronic Resource
    Electronic Resource
    Local characterization of electronic transport in microcrystalline silicon thin films with submicron resolution (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1475-1477 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional maps of dark conductivity with submicron resolution have been obtained on in situ prepared hydrogenated microcrystalline silicon (μc-Si:H) layers used for solar cells by atomic force microscopy with conductive cantilever. Comparison of the morphology and current image allows clear identification of Si crystallites. Pronounced current decrease has been detected at the grain boundaries. The technique was used to study initial stages of μc-Si:H growth, and we show how the incubation layer, detrimental for solar cells efficiency, can be minimized by pulsed excimer laser crystallization of the initial amorphous layer. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123585
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  • 8
    Electronic Resource
    Electronic Resource
    Transport study of self-supporting porous silicon (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1098-1100 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured dark DC conductivity and time-of-flight (TOF) of carriers in self-supporting porous silicon films in the temperature range 298–480 K. The dark I-V curves show superlinear behavior with activation energies of 0.38–0.67 eV. The TOF measurements allowed us to evaluate the drift-length of non-equilibrium carriers and revealed a significant decrease of the collected charge with increasing delay (tdel≥1 ms) of the exciting 3 ns laser pulse after the voltage application, probably due to field redistribution in the Si crystallites. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113584
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  • 9
    Electronic Resource
    Electronic Resource
    Photoelectric properties of self-supporting porous silicon (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3118-3120 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present transient and steady-state photocurrent data, measured in a special sample holder on a self-supporting porous silicon (PS) sandwich structure. Although the value of the drift mobility is difficult to find, we have estimated on the basis of the time of flight (TOF) technique the trap controlled value of mobility-lifetime product (μDτD) and from the steady-state photocurrent we have deduced recombination controlled (μτ)ss value. Surprisingly (μτ)ss〈μDτD. Charge collection is very low (about 1%) even for electric field F≈105 V/cm. However, the "schubweg''=μτF is (for η≈10% and F=108 V/cm) about 1 μm, much more than the quantum size dimensions (2–5 nm).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111366
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  • 10
    Electronic Resource
    Electronic Resource
    Formation of luminescent silicon by laser annealing of a-Si:H (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2555-2556 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the preparation of luminescent Si by laser annealing of amorphous hydrogenated silicon (a-Si:H) deposited on a silica substrate by glow-discharge deposition. For this process, we have used XeCl excimer laser pulses with an energy density in the range of 0.3–0.7 J/cm2. While no visible photoluminescence (PL) has been observed at room temperature from the unirradiated a-Si:H the PL comparable to the PL spectra of porous Si occurs in the irradiated part. The electron microscope studies reveal a microstructure which is a function of the pulse number and the pulse energy density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111572
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