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  • 1990-1994  (20)
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  • 1
    Electronic Resource
    Electronic Resource
    Density of amorphous Si (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 437-439 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The density of amorphous Si has been measured. Multiple Si implants, at energies up to 8.0 MeV, were made through a contact mask to produce alternating amorphous/crystalline Si stripes with amorphous thicknesses up to ∼5.0 μm. For layers up to 3.4 μm (5 MeV), the amorphous Si is constrained laterally and deforms plastically. Above 5 MeV, plastic deformation of the surrounding crystal matrix is observed. Height differences between the amorphous and crystalline regions were measured for as-implanted, thermally relaxed, and partially recrystallized samples using a surface profilometer. Combined with ion channeling measurements of the layer thickness, amorphous Si was determined to be 1.8±0.1% less dense than crystalline Si (4.90×1022 atom/cm3 at 300 K). Both relaxed and unrelaxed amorphous Si show identical densities within experimental error (〈0.1% density difference).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111121
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  • 2
    Electronic Resource
    Electronic Resource
    Nucleation and deposition of W on GaAs by excimer laser-assisted chemical vapor deposition (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1981-1988 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated laser-assisted chemical vapor deposition of W on GaAs to get insight into the deposition mechanism involved. Depositions were performed with an ArF excimer laser aligned parallel to the substrate and with WF6 and H2 as precursor and reducing agents, respectively. Samples were analyzed by Rutherford backscattering spectrometry and the sheet resistance was measured with a four-point probe. We investigated the temperature dependence of the deposition rate up to 400 °C for both laser-assisted and thermal deposition. At 350 °C and a laser repetition frequency of 20 Hz, we observed a deposition rate for laser-assisted deposition of 5.3 A(ring)/s, whereas without laser irradiation no deposition occurred. At this temperature, the film resistivity was 11 μΩ cm. For deposition temperatures above 350 °C, anomalous behavior was observed in both deposition rate and film resistivity. Experiments in which W coverage was measured as a function of laser pulse repetition frequency and as a function of time revealed that laser-assisted deposition at 300 °C consists of a two-step process. The first phase consists of exclusively laser-induced deposition at a rate of 3.3×1015 atoms/cm2/min/Hz, until a W coverage of approximately 15×1015 atoms/cm2 is reached. Laser-independent growth was not observed probably through insufficient nucleation. The second phase consists of combined laser-induced and laser-independent deposition on the initial W layer. The laser-induced growth rate was 3.2×1015 atoms/cm2/min/Hz for repetition frequencies in excess of 5 Hz. At 20 pulses per second, laser-induced deposition formed 47% of the total deposition rate. Below 5 Hz, the laser-induced rate was higher than above 5 Hz but nonlinear with pulse frequency. The growth rate by laser-independent deposition was 72×1015 atoms/cm2/min at 300 °C, which corresponds well with theory for thermally activated deposition of W on W.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353163
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  • 3
    Electronic Resource
    Electronic Resource
    Tungsten deposition on GaAs using WF6 and atomic hydrogen (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1989-1992 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tungsten was deposited on GaAs employing WF6 as precursor gas. A comparison is made between molecular and atomic hydrogen as reducing agent. Atomic hydrogen is produced in situ by dissociating molecular hydrogen on a hot (2100 °C) filament. Tungsten deposition was not observed only when molecular hydrogen and the substrate were available as reducing agents. Introduction of atomic hydrogen did lead to W deposition on GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353164
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  • 4
    Electronic Resource
    Electronic Resource
    Pulsed-laser crystallization of amorphous silicon layers buried in a crystalline matrix (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4024-4035 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion implantation, employing Si, Ar, and Cu ions in the energy range from 275 to 600 keV, was used to form amorphous silicon layers buried in a crystalline matrix. Different layer geometries were produced, with 150–620-nm-thick amorphous layers, separated from the surface by 120–350-nm-thick crystalline layers. Crystallization of the amorphous layers was induced by 32-ns pulsed ruby laser irradiation. Real-time reflectivity and conductivity measurements indicate that internal melting can be initiated at the amorphous-crystalline interface, immediately followed by explosive crystallization of the buried layer. Channeling and cross-section transmission electron microscopy reveal that in both Si(100) and Si(111) samples explosive crystallization proceeds epitaxially with twin formation, the twin density being higher in Si(111) than in Si(100). The measured crystal growth velocities range from 15 to 16 m/s, close to the fundamental limit for crystalline ordering at a Si liquid-crystalline interface. Computer modeling of heat flow and phase transformations supports the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346076
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  • 5
    Electronic Resource
    Electronic Resource
    3D-resolved determination of minority-carrier lifetime in planar silicon solar cells by photocurrent decay (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6485-6494 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In modern production schemes for Si solar cells, defect passivation and impurity gettering are often used to improve material quality and thereby cell efficiency. These processes generally alter the spatial uniformity of minority-carrier transport parameters over the wafer and may result in minority-carrier lifetime and diffusion length variations both lateral and in depth. In polycrystalline Si these spatial dependences are already present due to the nature of the material. We present an extension of the photocurrent decay method to determine the diffusion length in a three-dimensionally resolved fashion. From a single photocurrent decay curve the back-surface recombination velocity, the average minority-carrier diffusion length, and an asymmetry factor which qualitatively describes the depth dependence of the diffusion length are determined. This is done using the three observables: quantum efficiency, fundamental decay time, and intercept of the extrapolated decay curve with the time-zero axis. Lateral resolution is obtained by focusing the light beam to a small spot on the cell and measuring the current decay curve as a function of position on the cell. It is shown that light-pulse durations longer than the minority-carrier lifetime and wavelengths longer than 950 nm are required. These conditions are met by using modulated wavelength-tunable light from a Ti:sapphire laser. Measurements on monocrystalline cells show that the decay time is independent of wavelength and light-pulse duration, as predicted by theory. Furthermore, the intercept with the time-zero axis was shown to increase with increasing pulse duration and wavelength. Measurements on a set of polycrystalline Si cells were performed showing that gettering treatments during cell production result in depth-dependent lifetimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346847
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  • 6
    Electronic Resource
    Electronic Resource
    Raman study of de-relaxation and defects in amorphous silicon induced by MeV ion beams (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2097-2099 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectroscopy is used as a probe of the state of amorphous Si (a-Si) and damaged crystalline Si. MeV ion beams have been used to irradiate structurally relaxed a-Si. When the density of Si atoms displaced by nuclear collisions exceeds 5%, the a-Si is "de-relaxed'', and thus returns to its as-implanted state. This behavior is an indication that point defect complexes exist in a-Si and play an important role in the process of structural relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102984
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  • 7
    Electronic Resource
    Electronic Resource
    Combined impurity gettering and defect passivation in polycrystalline silicon solar cells (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2704-2706 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline silicon wafers have been subjected to annealing (700 °C, 1 h) and to a hydrogen plasma (350 °C, 30 min) during the processing of solar cells. The annealing treatment enhances the bulk minority-carrier recombination lifetime by 19%, presumably by impurity gettering. The plasma treatment improves the lifetime by 26%; hydrogen passivation accounts for at least 2/3 of this improvement. Gettering and passivation are found to be complementary: application of both treatments results in a 43% increase in lifetime compared to standard.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103805
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  • 8
    Electronic Resource
    Electronic Resource
    Boron doping of silicon using coalloying with aluminium (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2792-2794 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a new technique for boron (B) doping of silicon. In this letter we show that a B doping profile of more than 2 μm thickness with a maximum active doping concentration of 3×1019 cm−3 can be formed by a fast (〈1 min) alloying process at a temperature of 850 °C. Thick-film aluminum is used to obtain an alloying and epitaxial regrowth process in accordance with the Al–Si phase diagram. The atomic concentration profile of the B- and Al-doped Si layer was determined by secondary ion mass spectrometry. The active doping concentration was measured with an automatic electrochemical capacitance/voltage profiler. By the addition of B to the Al paste, the epitaxially regrown layer is doped with B and Al to the solid solubility of these elements in Si at the particular regrowth temperature. The applicability of this fast low temperature B doping process in Si solar cell processing is discussed. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112992
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  • 9
    Electronic Resource
    Electronic Resource
    Defects in amorphous silicon probed by subpicosecond photocarrier dynamics (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1688-1690 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photocarrier dynamics in pure nonhydrogenated amorphous silicon (a-Si) have been studied with subpicosecond resolution using pump-probe reflectivity measurements. The photocarrier lifetime increases with the annealing temperature from 1 ps for as-implanted a-Si to 11 ps for a-Si annealed at 500 °C. The lifetime in annealed a-Si can be returned to the as-implanted level by ion irradiation. These observations indicate that a-Si can accommodate a variable number of defect-related trapping and recombination centers. The saturated defect density in as-implanted a-Si is estimated to be ≈1.6 at. %. Comparison with Raman spectroscopy suggests that various kinds of structural defects are present in a-Si.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107212
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  • 10
    Electronic Resource
    Electronic Resource
    Defect states of amorphous Si probed by the diffusion and solubility of Cu (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1230-1232 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusivity and solubility of Cu impurities have been measured in different structural states of amorphous Si (a-Si) formed by MeV Si implantation. The 2.2-μm-thick a-Si layers were first annealed (structurally relaxed) at 500 °C and then implanted with 200 keV Cu ions, returning a 300-nm-thick surface layer to the as-implanted state. After diffusion at temperatures in the range 150–270 °C, we observe solute partitioning at a sharp phase boundary between the annealed and Cu-implanted layers, the partition coefficient being as large as 8.2±1.3. The diffusion coefficient in annealed a-Si is 2–5 times larger than in as-implanted a-Si, with activation energies of 1.39±0.15 and 1.25±0.04 eV, respectively. The data show quite strikingly the role which defects can play in the a-Si structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103493
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