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  • 1
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1097-1099 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is shown that amorphous silicon can be transformed to monocrystalline silicon via an explosive epitaxial crystallization process induced by pulsed laser irradiation. 370-nm-thick amorphous Si layers, buried beneath a 130-nm-thick crystalline surface layer, were irradiated with a 32 ns ruby laser pulse. Real-time reflectivity measurements indicate that internal melting can be initiated at the amorphous-crystalline interface, immediately followed by explosive crystallization of the buried amorphous Si layer. Channeling and cross-sectional transmission electron microscopy reveal that explosive crystallization proceeds epitaxially with formation of twins extending into the sample. The crystal growth velocity is determined to be 16.2±1.2 m/s, close to the fundamental limit for crystalline ordering at a liquid Si/Si(100) interface.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 437-439 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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).
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1981-1988 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6596-6603 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The efficiency of silicon solar cells can be increased by reducing the recombination of minority carriers at the backsurface of a cell. This can be achieved by application of a low-high junction, commonly called a backsurface field (BSF). The dependence of the effective backsurface recombination velocity Seff of a BSF on the BSF doping profile and the base doping concentration was studied experimentally. The doping profiles were analyzed using sheet resistance measurements, stripping Hall measurements, and secondary ion mass spectrometry. The effective recombination velocity was obtained from photoconductivity decay probed with microwaves on symmetrical p+pp+ structures, and from photocurrent decay measurements on n+pp+ solar cells. The measured values of Seff were compared with calculated values, based on the measured doping profiles. Both from photoconductivity and photocurrent decay measurements, Seff was found to decrease with an increasing difference in acceptor concentration between the BSF and the base of the solar cell. The measured values of Seff, obtained with the two experimental techniques, are in agreement with each other. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1989-1992 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1497-1504 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The sensitivity of a contactless measurement procedure to determine the minority-carrier recombination parameters in Si wafers is analyzed. The measurement is based on the harmonic generation of excess carriers, whose time dependence is measured either by μ-wave reflection or free-carrier absorption. Both the measurement equipment and the model used to extract the surface recombination velocity and the bulk carrier lifetime are introduced and the sensitivity of the parameter fit procedure is examined. The results of this uncertainty analysis are applied to typical experimental situations, e.g., bulk minority carrier lifetime measurement of a monocrystalline wafer with equal surfaces or a bulk minority carrier lifetime mapping done on an as-grown multicrystalline Si wafer before it obtained saw damage removal. The method proves to be very useful, if the interpretation of the results is carefully done and an appropriate experiment is chosen to produce the best possible results. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4024-4035 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6485-6494 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2097-2099 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2704-2706 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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