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  • 1
    Electronic Resource
    Electronic Resource
    Deposition of amorphous silicon films by hot-wire chemical vapor deposition (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6843-6852 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Device-quality a-Si:H films have been deposited by hot-wire chemical vapor deposition (HWCVD). We have investigated the influence of deposition parameters on the film growth and properties. The most important deposition and growth processes that influence the optoelectronic material properties of a-Si:H deposited by HWCVD are clarified. During the deposition process attention must be paid to accurately control the substrate temperature, which is a key parameter to obtain device-quality films. A heat transport model is presented to be able to correct for the heating of the substrate by the filaments. It is found that films deposited at high deposition temperatures are under a high compressive stress. We show how the hydrogen incorporation in the layer is influenced by hydrogenation of subsurface layers by the atomic hydrogen flux that is inherent to the HWCVD process. We further identify the fundamental differences between plasma enhanced CVD and HWCVD material. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370202
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  • 2
    Electronic Resource
    Electronic Resource
    Photovoltaic effects in porphyrin polymer films and heterojunctions (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3381-3389 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electropolymerized porphyrin films on indium–tin–oxide substrates have been characterized using Rutherford backscattering spectrometry, absorption spectroscopy, electrical characterization methods and with step profiling. With these methods the density of the films (ρ=1.35 g/cm3) and the absorption coefficients α(λ) have been determined. For film thicknesses exceeding 40 nm, silver electrical contacts without shunts are achieved by evaporation. The dark conductivity of the films amounts to 10−13–10−12 Ω−1 cm−1. When applying a band model for the conduction in the films, the dark space charge limited current and the exponent in the relation between photoconductivity and illumination intensity (σ∼Iγ, γ=0.65±0.05) indicate an exponential trap distribution in the band gap of the films. From the action spectra, filter effects of the photoconductance and low mobilities are inferred. Spin coating of acceptor layers on top of the polymer films results in the formation of heterojunctions showing photovoltaic behavior, with an open-circuit voltage 0.4–0.6 V. The short-circuit current is controlled by electron transfer at the donor/acceptor interface only and is limited by filter effects in the bulk and by the low conductivity of the materials. The optoelectrical properties of the layers are different if analyzed using a mercury contact (higher dark conductivity, no photoconductivity) which is attributed to the intro- duction of dopants from ambient air in this case. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363203
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  • 3
    Electronic Resource
    Electronic Resource
    Significance of tunneling in p+ amorphous silicon carbide n crystalline silicon heterojunction solar cells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2609-2611 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We used the internal photoemission (IPE) technique to accurately determine the valence and conduction band offsets at the a-SiC:H/c-Si interface and investigated with numerical simulations their effects on the photocarrier collection in p+ a-SiC:H/n c-Si heterojunction solar cells. The valence and conduction band discontinuities were found to be 0.60 and 0.55 eV, respectively. However, despite the large barrier at the valence band edge, 30 nm p+ a-SiC:H/n c-Si heterojunction solar cells show no collection problems due to blocking of holes (FF=0.73). Combined IPE measurements and simulation results indicate that tunneling of holes through this barrier at the valence band edge can explain the unhindered collection. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122521
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  • 4
    Electronic Resource
    Electronic Resource
    Stable amorphous-silicon thin-film transistors (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2681-2683 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogenated amorphous silicon, a-Si:H, prepared with the hot-wire chemical vapour deposition technique is incorporated in thin-film transistors (TFTs). High-quality TFTs are fabricated with this type of a-Si:H, which we deposited at a rate of 17 Å/s. TFTs with a current switching ratio of 5×105, a threshold voltage of 6.3 V, and an electron field-effect mobility in the saturation regime of 0.6 cm2/V s are obtained. These TFTs do not show any threshold voltage shift upon prolonged gate voltage application, in contrast to conventional a-Si:H TFTs. This has been achieved by optimizing the electronic properties of the hot-wire layer, and by optimizing the interface between the gate dielectric and the hot-wire layer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118992
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  • 5
    Electronic Resource
    Electronic Resource
    Improving tunneling junction in amorphous silicon tandem solar cells (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1871-1873 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report new results on a tunneling junction in amorphous silicon tandem solar cells using the metal oxide, niobium oxide (NbOx ), as the recombination layer and the advanced doping gas, trimethylboron [B(CH3 )3 ], in the p+ layer. The new tunneling junction has a low series resistance and minimizes optical loss. The advantage of the NbOx layer is its high transparency, hence a relatively thick (∼10 nm) layer can be used. The ability to use a thick oxide layer is important for the implementation of the tunneling junction in the production of large-area panels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103073
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  • 6
    Electronic Resource
    Electronic Resource
    Performance of heterojunction p+ microcrystalline silicon n crystalline silicon solar cells (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 6089-6095 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied by Raman spectroscopy and electro-optical characterization the properties of thin boron doped microcrystalline silicon layers deposited by plasma enhanced chemical vapor deposition (PECVD) on crystalline silicon wafers and on amorphous silicon buffer layers. Thin 20–30 nm p+ μc-Si:H layers with a considerably large crystalline volume fraction (∼22%) and good window properties were deposited on crystalline silicon under moderate PECVD conditions. The performance of heterojunction solar cells incorporating such window layers were critically dependent on the interface quality and the type of buffer layer used. A large improvement of open circuit voltage is observed in these solar cells when a thin 2–3 nm wide band-gap buffer layer of intrinsic a-Si:H deposited at low temperature (∼100 °C) is inserted between the microcrystalline and crystalline silicon [complete solar cell configuration: Al/(n)c-Si/buffer/p+μc-Si:H/ITO/Ag)]. Detailed modeling studies showed that the wide band-gap a-Si:H buffer layer is able to prevent electron backdiffusion into the p+ μc-Si:H layer due to the discontinuity in the conduction band at the amorphous-crystalline silicon interface, thereby reducing the high recombination losses in the microcrystalline layer. At the same time, the discontinuity in the valence band is not limiting the hole exit to the front contact and does not deteriorate the solar cell performance. The defect density inside the crystalline silicon close to the amorphous-crystalline interface has a strong effect on the operation of the cell. An extra atomic hydrogen passivation treatment prior to buffer layer deposition, in order to reduce the number of these defects, did further enhance the values of Voc and fill factor, resulting in an efficiency of 12.2% for a cell without a back surface field and texturization. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366479
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  • 7
    Electronic Resource
    Electronic Resource
    A self-consistent analysis of temperature-dependent field-effect measurements in hydrogenated amorphous silicon thin-film transistors (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 643-649 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We calculated a more accurate density of states (DOS) profile from field-effect (FE) measurements in hydrogenated amorphous silicon thin-film transistors, taking into account the anomalously changing conductivity prefactor in accordance with the Meyer–Neldel (MN) rule. We present a self-consistent analysis of the density of gap states profile, where the MN rule is, for the first time, properly considered in relation to the nonuniform shift of the Fermi level as induced by the field effect. Moreover, the calculation yields the correct flat-band voltage and the corresponding flat-band activation energy. The determination of conductivity activation energies free from any initial band bending effects is of importance in all types of transport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337407
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  • 8
    Electronic Resource
    Electronic Resource
    Interpretation of the silicon-hydrogen stretching doublet in a-Si:H hydrogenated amorphous silicon (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 204-206 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the correlation between the infrared integrated absorption strengths of the wagging, bending and stretching modes for four hydrogenated amorphous silicon (a-Si:H) series, deposited by rf glow discharge. The strength of these modes was varied by changing the deposition temperature while keeping other parameters fixed. For the first time it is shown that a straightforward correlation exists between these three modes. It is argued that the 2100-cm−1 mode is due to SiH2 bonds and that there is no contribution of SiH species on the inner surface of voids. The vibrational spectrum of a-Si:H can be well described by considering the vibrating dipole as a harmonic oscillator with an effective charge e*=0.44 electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112995
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  • 9
    Electronic Resource
    Electronic Resource
    Stability of hot-wire deposited amorphous-silicon thin-film transistors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1062-1064 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the first time hydrogenated amorphous silicon, a-Si:H, deposited with the hot-wire technique is incorporated in thin-film transistors (TFTs). Amorphous silicon was deposited at a rate of 20 A(ring)/s. TFTs with a switching ratio of 105, a threshold voltage of 16.9 V, and a field-effect mobility μs of 0.001 cm2/V s are obtained. Upon gate voltage stress, virtually no change in any of these TFT parameters is observed. Conventional state-of-the-art TFTs deposited in a 13.56 MHz glow discharge showed a threshold voltage shift of more than +12 V. The interface between the gate dielectric and the hot-wire a-Si:H layer needs further optimization. After gate voltage stress, the TFTs containing hot-wire a-Si:H have superior quality with respect to the threshold voltage. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116931
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  • 10
    Electronic Resource
    Electronic Resource
    High energy-barrier for defect creation in thin-film transistors based on hot-wire amorphous silicon (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3674-3676 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin-film transistors based on amorphous silicon deposited by hot-wire chemical-vapor deposition (CVD) exhibited a high mean barrier height of 1.074 eV for defect creation after gate-voltage stress. This is 77 meV higher than for glow-discharge devices. Transistors with a SiO2 or a-SiNx:H gate dielectric showed good performance with a field-effect mobility up to 0.7 cm2/V s. Thus, good thin-film transistors with a superior stability can be deposited by hot-wire CVD at high deposition rates of 1.7 nm/s. We demonstrate that a reduced defect creation in the silicon and not the hot-wire-specific absence of interface ion bombardment is responsible for this higher stability. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125425
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