208 research outputs found

    Theory of superfast fronts of impact ionization in semiconductor structures

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    We present an analytical theory for impact ionization fronts in reversely biased p^{+}-n-n^{+} structures. The front propagates into a depleted n base with a velocity that exceeds the saturated drift velocity. The front passage generates a dense electron-hole plasma and in this way switches the structure from low to high conductivity. For a planar front we determine the concentration of the generated plasma, the maximum electric field, the front width and the voltage over the n base as functions of front velocity and doping of the n base. Theory takes into account that drift velocities and impact ionization coefficients differ between electrons and holes, and it makes quantitative predictions for any semiconductor material possible.Comment: 18 pagers, 10 figure

    Dynamic avalanche breakdown of a p-n junction: deterministic triggering of a plane streamer front

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    We discuss the dynamic impact ionization breakdown of high voltage p-n junction which occurs when the electric field is increased above the threshold of avalanche impact ionization on a time scale smaller than the inverse thermogeneration rate. The avalanche-to-streamer transition characterized by generation of dense electron-hole plasma capable to screen the applied external electric field occurs in such regimes. We argue that the experimentally observed deterministic triggering of the plane streamer front at the electric field strength above the threshold of avalanche impact ionization but yet below the threshold of band-to-band tunneling is generally caused by field-enhanced ionization of deep-level centers. We suggest that the process-induced sulfur centers and native defects such as EL2, HB2, HB5 centers initiate the front in Si and GaAs structures, respectively. In deep-level free structures the plane streamer front is triggered by Zener band-to-band tunneling.Comment: 4 pages, 2 figure

    Impact ionization fronts in Si diodes: Numerical evidence of superfast propagation due to nonlocalized preionization

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    We present numerical evidence of a novel propagation mode for superfast impact ionization fronts in high-voltage Si p+p^+-nn-n+n^+ structures. In nonlinear dynamics terms, this mode corresponds to a pulled front propagating into an unstable state in the regime of nonlocalized initial conditions. Before the front starts to travel, field-ehanced emission of electrons from deep-level impurities preionizes initially depleted nn base creating spatially nonuniform free carriers profile. Impact ionization takes place in the whole high-field region. We find two ionizing fronts that propagate in opposite directions with velocities up to 10 times higher than the saturated drift velocity.Comment: 3 pages, 4 figure

    Tunneling-assisted impact ionization fronts in semiconductors

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    We propose a novel type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp (10kV/ns\sim 10 {\rm kV/ns}) is applied in reverse direction to a Si p+nn+p^+-n-n^+-structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns. The maximal electrical field at the front edge exceeds 106V/cm10^6 {\rm V/cm}. The front velocity vfv_f is 40 times faster than the saturated drift velocity vsv_s. The front passes through the nn-base with a thickness of 100μm100 {\mu m} within approximately 30 ps, filling it with dense electron-hole plasma. This passage is accompanied by a voltage drop from 8 kV to dozens of volts. In this way a voltage pulse with a ramp up to 500kV/ns500 {\rm kV/ns} can be applied to the load. The possibility to form a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.Comment: 12 pages, 6 figure

    Reversed Switch-On Dynistor Switches of Gigawatt Power Microsecond Pulses

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    A high-power (250 kA and 25 kV) compact switch based on an assembly of reversed switch-on dynistors (RSDs) connected in series and a coaxial saturable-core choke, which is necessary for their effective switching, is described. An essential feature of this switch is a drastic reduction of the duration of RSDs control pulse, which allows using minimum dimensions and low inductance saturable core choke and obtain high rise rate (more than 30 kA/µs) of the switched current. The increased RSDs control pulse amplitude and rise rate that are required for RSDs switching on by reduced duration triggering pulse are attained by using a fast switch based on new type semiconductor devices deep-level dynistors (DLDs)

    The value of the quality of forensic medical examination of the corpse for the investigator.

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    The influence of the defect of forensic examination of the corpse on the work of the investigative bodies has been shown. The need to control the quality of the forensic medical expert with the corpse and the feasibility of developing criteria for the quality of professional activity of the expert was determined.Показано влияние дефекта судебно-медицинского исследования трупа на работу следственных органов. Определена необходимость контроля качества работы судебного медика с трупом и целесообразность разработки критериев качества профессиональной деятельности эксперта
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