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  • 1
    Electronic Resource
    Electronic Resource
    Prebreakdown and breakdown phenomena in high-field semiconductor-dielectric systems (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7643-7666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complexity of the semiconductor-dielectric system behavior under high electric fields is discussed. Time dependence of the voltage drop, electrical current, and light emissions, and the strong influence of the nature and quality of the surrounding dielectric, as well as the quality of the semiconductor processing and contacts, are analyzed for high-purity bulk silicon-dielectric vacuum or gas systems under impulse voltage stress. On the basis of the analysis of the main characteristics of the time response of the system up to breakdown, as well as of the variation of the current components with the applied voltage, a new comprehensive physical model of the prebreakdown and breakdown phenomena in the high-field semiconductor-dielectric systems is proposed. The model points out the active behavior of two parts, the semiconductor and the ambient dielectric, and the main role of the semiconductor in the initiation of the breakdown phenomena in the system. Based on a large number of experimental results, the present model proposes two totally different breakdown processes in semiconductor-dielectric systems: surface flashover and semiconductor bulk breakdown, depending on the defect distribution in the semiconductor. The key to the model is offered by the role of the conduction currents in the semiconductor, especially by the local avalanche current generated by avalanche processes in defect zones of the crystal, for fields much smaller than the theoretical intrinsic breakdown field of the material. The main characteristics of the prebreakdown and breakdown response of the system for different conditions are explained on the basis of the proposed model. A short discussion of the main reported results of other groups is also presented in view of the new physical model. The role of the semiconductor and ambient-dielectric quality, as well as of the system configuration quality in the breakdown phenomena of high-field semiconductor-dielectric systems, are emphasized on the basis of the proposed model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353962
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  • 2
    Electronic Resource
    Electronic Resource
    Time-resolved prebreakdown x-ray emission from polycrystalline alumina-bridged vacuum gaps for impulse stresses (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2181-2188 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved and time-coordinated observations of voltage and prebreakdown and breakdown x-ray emission associated with the surface flashover of ceramic-insulator-bridged vacuum gaps for pulsed excitations 0.15/20 μs are described. 99.9% pure polycrystalline alumina right circular cylinders (25.4 mm diam, 10 mm tall) were investigated. The alumina samples were of two types, i.e., machined on the cylindrical surface to (i) 0.8 μm surface finish and (ii) 0.25 μm surface finish. An inverse correlation between the frequency of occurrence of prebreakdown x-ray emission and the surface flashover strength is observed for all samples. The relationship between the onset time of the prebreakdown x-ray peak from voltage zero and the surface flashover strength, however, is seen to be in direct proportion, i.e., the longer the onset time of the x-ray peak from voltage zero, the higher is the flashover voltage. These novel experimental observations are analyzed to infer the origin of x radiation in the bridged vacuum gap and their dependence on the nature of the insulating surface. The results could not be explained satisfactorily by the conventional secondary emission avalanche theory. A thermally activated, field-assisted exoelectron emission model is believed to be in better qualitative agreement with the prebreakdown x-ray emission results reported here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351114
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  • 3
    Electronic Resource
    Electronic Resource
    Flashover in wide-band-gap high-purity insulators: Methodology and mechanisms (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6325-6333 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron beam of a scanning electron microscope (SEM) is used to charge an unmetallized insulator (Al2O3, Y2O3, SiO2) in vacuum. The charging is found to be stable in time after the e-beam is switched off. The SEM is also used to measure the implanted charge by measuring the resulting electrostatic potential. The distribution of potential around the trapped charges is determined by the classical laws of electrostatics. The electrostatic energy stored in the polarized dielectric can thus be determined. The implanted charge can be removed by the introduction of carriers into the polarized sample by flooding the surface with electron beams of varying energies. Slow or rapid relaxation occurs depending on the operating conditions of the flood gun (energy, intensity, etc.) which introduces the electrons. When the relaxation kinetics are slow, the electrostatic charge decreases slowly as a function of time. On the other hand, a rapid relaxation of the dielectric leads to the appearance of a high-density plasma which spreads over the insulator surface, resulting in treeing on the insulator surface. Along the path of the arc, the transfer of energy to the lattice triggers the sublimation of the ceramic and its mechanical fracture through thermal shock. At particular flood gun setup conditions, we have observed the formation of parallel fracture lines along the ceramic surface, away from the treeing region. These results constitute the basis for a new approach to understanding flashover along ceramics-vacuum interfaces. The important step is the plasma initiation, which we interpret on the basis of dielectric relaxation mechanisms. The parameter of the insulator that determines its breakdown initiation is its complex dielectric constant. It is concluded that the insulator's band gap, the nature and density of defects localized in the band gap, and the dipolar relaxation induced by a variation of the electric field and connected with the presence of defects determine the holdoff level of insulators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348831
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of electrical avalanches and optical radiation near solid insulators in high pressure (up to 0.3 MPa) nitrogen gas (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2877-2884 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron and ion avalanches have been recorded near a variety of insulators (plexiglas, teflon, high-density polyethylene, low-density polyethylene, polypropylene, delrin, polyvinyl chloride, and nylon) in nitrogen gas at pressures of 0.1, 0.2, and 0.3 MPa. With the exception of nylon, suppression of avalanches has been observed in the presence of insulators. In addition to electron and ion avalanches, simultaneous measurement of optical radiation associated with an electron avalanche was successfully carried out. Qualitative explanations have been provided for the suppression of avalanches near most insulators and an anomalous growth of avalanches near nylon insulators. Photoemission from nylon surfaces appears to be responsible for the enhanced growth of avalanches near nylon insulators. More precise measurements of optical radiation are needed to better understand the electron-photon interactions near a solid insulator in a gaseous dielectric medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348596
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  • 5
    Electronic Resource
    Electronic Resource
    Selective doping of 4H–SiC by codiffusion of aluminum and boron (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5647-5651 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A graphite mask was used to realize selective doping of aluminum/boron in 4H–SiC by thermal diffusion at a temperature range of 1800–2100 °C. The doping profiles investigated by secondary ion mass spectrometry show that a high aluminum concentration of 5×1019 cm−3 near the surface and linearly graded boron profile up to several micrometers in depth can be obtained. Hall effect measurement was also employed to obtain the electrical characteristics of the diffused region, from which the carrier concentration (1×1019 cm−3) and hole mobility (7 cm2/V s) at room temperature were extracted. Room temperature photoluminescence indicates that the dominant luminescence is attributed to the donor acceptor pair recombination, in which boron D complex is the prevailing center rather than Al and boron shallow acceptors. Cathodoluminescence micrographs clearly illustrate a pattern with the locally diffused regions. To confirm the viability of the diffusion process, planar p-n diodes with a fairly low forward voltage drop (3.3 V at 100 A/cm2) and high reverse blocking capability (more than 1100 V) were fabricated. Built-in voltage of 2.9 V, which is typical for 4H–SiC p-n diodes, was obtained by capacitance–voltage measurement. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415541
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  • 6
    Electronic Resource
    Electronic Resource
    A photoelectronic source for electron avalanche measurements (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 2495-2496 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A photoelectronic source described by Borghesani et al. [Rev. Sci. Instrum. 57, 2234 (1986)] employed a Xenon flash lamp to obtain relatively large electronic current pulses of microsecond duration. A theoretical analysis and a subsequent rule of thumb indicated that a minimum thickness of 50 A(ring) is needed for obtaining maximum electron yield through such a device. In this note, we report the fabrication details of a similar but a much faster response (∼1 ns) electrode system to produce an electron burst. The film thickness corresponding to maximum photoemission yield was estimated by using a crystal oscillator. Optimum thickness was found to be ∼100 A(ring) which is in general agreement with the earlier device having microsecond duration pulse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142222
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  • 7
    Electronic Resource
    Electronic Resource
    Surface filamentation in semi-insulating silicon (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8557-8564 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new field limit of silicon devices stressed at pulsed high fields is proposed, namely, the threshold field for the onset of the phase-shifted current response of the device. While the classical limit by the breakdown of the semiconductor-dielectric system, generally by surface flashover, causes a total damage of the semiconductor, the new limit prevents any damage of the device, even at high applied fields. Depending on the overall quality of the device under test, catastrophic failure of the device can be avoided even at large fields of ∼70 kV/cm by not exceeding the threshold for the onset of the phase-shifted current response, the proposed new field limit. Beyond this limit the device response is unstable and a surface filament, distinctly different from the surface flashover tracks, may appear on the device surface, permanently degrading its quality. Experimental results are presented supporting the new predamage high-field limitation. Scanning electron microscopy and optical micrographs are presented for a clear description of the nature of the damage. The present results are discussed using a recent physical model of prebreakdown and breakdown phenomena in high-field semiconductor-dielectric systems [G. Gradinaru and T. S. Sudarshan, J. Appl. Phys. 73, 7643 (1993)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362536
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  • 8
    Electronic Resource
    Electronic Resource
    Dielectric surface preflashover processes in vacuum (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3313-3320 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Surface preflashover phenomena across alumina ceramics in vacuum are presented. The localized plasmas are identified by the spatially resolved images that appear in a pulse surface preflashover phase using an intensified charge-coupled-device camera, along with coordinated, time-resolved preflashover current and luminosity. It was observed that significant preflashover activity associated with the localized plasmas on the surface appears after a flashover event and disappears after a few pulse voltage applications. Large bursts of current pulses (several hundred milliamperes) with no counterpart in the luminosity signal were also observed during preflashover. These phenomena cannot be explained satisfactorily by electron stimulated gas desorption. The effect of adsorbed gases and surface polishing on preflashover are presented and discussed. The experimental results indicate that preflashover essentially depends on the surface state (physical and chemical) of the solid insulator. The preflashover conduction associated with the localized plasmas is attributed to the detrapping and impact-ionization processes associated with defect centers. The results reported support the surface flashover model based on trapping/detrapping and impact ionization processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357453
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of the scanning electron microscope mirror image based on the dielectric surface microstructure (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3715-3722 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper addresses hitherto unexplained phenomena associated with the electrostatic mirror technique, such as (i) the influence of the surface microstructural parameters of a polycrystalline dielectric (e.g., alumina) on mirror images, and (ii) the distortion of mirror images. The formation of a mirror image on an as-machined alumina surface was found to be nearly impossible, but on a polished specimen, possessing low surface damages, mirror images were easily formed. A smooth and low-damage surface seems to be a prerequisite for the formation of a mirror image. The size of mirror images, observed at different locations on a polished alumina surface, was found to vary significantly, indicating that an inhomogeneous surface charging occurs in polycrystalline dielectrics. It was shown that the variation in the grain and grain boundary volumes constituting the charged region is responsible for the variation in the size of the mirror image. The distortion of the mirror images was studied using single crystal quartz specimens. The asymmetry of the equipotential boundary—caused by (i) the tilt of the crystal axis (θ≠0°) with respect to the probing electron beam, or by (ii) the asymmetrical electron interaction volume, i.e., deviation from the standard pear shape—was demonstrated to be responsible for the distortion of the mirror images.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356043
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  • 10
    Electronic Resource
    Electronic Resource
    Electrocathodoluminescence in insulator-bridged vacuum gaps under high-voltage stress (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3711-3719 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface glow associated with Lucalox alumina insulator under high-voltage dc and ac stress in bridged vacuum gaps was determined to be a continuum radiation with band limits from about 220 to 500 nm with a peak around 320 nm. A second peak with very low intensity was observed at longer wavelengths. Such surface luminescence from other materials (including different types of alumina) bridging the vacuum gap was either absent or too weak to be analyzed. There is ample evidence to support the view that the observed glow with Lucalox (99.9 wt. % Al2O3) is associated with electronic transitions between quantum-mechanical states at defect sites (either interstitial atoms or vacancies) in the crystal structure of Al2O3. These defect sites are either the F+ centers (one electron trapped at an anion vacancy, i.e., Al2+ ion) or the F centers (two electrons trapped at an anion vacancy, i.e., Al+ ion). The results of this investigation indicate that the observed luminous front along an insulator surface in vacuum, prior to flashover, is not necessarily indicative of a streamer-type discharge development in the gas phase, desorbed from the insulator surface. Such a luminous front is indicative of electronic transitions at defect sites located at or near the insulator surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337580
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