Effect Of Secondary Ionization Research Articles

BV/sub CEO/--BV/sub CBO/ separation and sharpness of breakdown in high-speed bipolar transistors

The effect of secondary impact ionization by the noninitiating carrier on the near avalanche behavior of high-speed n-p-n bipolar transistors is studied. We show that secondary collector ionization by generated holes traveling back toward the base layer significantly reduces BV/sub CBO/ if the hole ionization coefficient is higher than that of electrons [/spl beta//sub p/(E)>/spl alpha//sub n/(E)]: positive feedback associated with a strong secondary ionization sharpens the breakdown characteristic by speeding up carrier multiplication and decreases separation between the open-base collector-emitter (BV/sub CEO/) and the open-emitter base-collector (BV/sub CBO/) breakdown voltages. The effect of secondary ionization on the BV/sub CEO/-BV/sub CBO/ separation has not previously been described. Multiplication coefficient comparisons for representative InP, GaAs, and Si collectors indicate all structures can sustain low-current above BV/sub CEO/ operation from a transport (nonthermal) point of view, although the different degrees of secondary ionization in various semiconductors lead to fundamental differences when InP is compared to GaAs and Si since for the latter materials /spl beta//sub p/(E)</spl alpha//sub n/(E). The collector ionization integral is used to determine the maximum collector voltage before the onset of nonthermal device instabilities for InP devices: we find that for a 2000-/spl Aring/ collector the transistor can be operated well above BV/sub CEO/ and up to 90% of BV/sub CBO/ when the base is not left open-circuited, in good agreement with previously reported measurements on InP/GaAsSb/InP double heterojunction bipolar transistors.

A study of the behavior of a d.c. pulsed low pressure point-to-plane discharge

A numerical study of a nitrogen cold plasma created by a pulsed discharge in a point-to-plane geometry at 4 torr is presented. The relative model is based on fluid description of the cold plasma, on Poisson's equation for the electric field and on balance equations for the excited population concerning only some vibrational band of molecular nitrogen (C 3 ∏ u , B 3 ∏ g and A $^3\sum_{\rm u}^+$ ). Secondary ionization phenomena and longitudinal diffusion effects are included in the model and their contribution to the glow-discharge establishment is studied. Results for space and time variations of the charged particles, electric field, potential and electronic current densities are reported. Particular attention was paid to the physical factors forming the cathodic layer and influencing its evolution. Results concerning the influence of the electronic current density on the creation of excited (radiative and metastables) particles are presented. According to these results, the plasma of the glow discharge occurs by means of three successive sequences with different characteristics. During the first sequence the gap is slowly filled of ions formed close to the anode, then in the second one an ionizing front formed close to the anode is propagating towards the cathode with an average velocity of 2 × 10 6 cm/s. It forms the cathodic layer zone and starts the participation of the secondary ionization effects leading to the third sequence which deals with the glow discharge establishment. The first significant production of excited states occurs within the ionizing front but the most important one is obtained when the glow discharge is established. It has been shown that at 4 torr and a gap of 1 cm, a mean electronic current density of 5 mA/cm 2 is sufficient to create 10 9 cm −3 of (B 3 ∏ g , v = 0), 10 8 cm −3 of (C 3 ∏ u , v = 0) and 10 11 cm −3 of (A $^3\sum_{\rm u}^+$ , v = 0 ) excited particles.

Laser‐induced burst corona and streamer corona for a positive DC nonuniform field gap in N2/NO mixtures

AbstractThe characteristic of sparkover in a DC nonuniform field gap is closely related to the discharge mode at the onset time of corona. In order to investigate the transition mechanism from burst corona to glow corona or streamer corona, a discharge experiment which is controlled by a pulsed laser in N2/NO mixture has been performed.From highly sensitive observation of discharge luminescence which corresponds to the discharge current wave, the transition from burst corona to streamer corona is identified by the electron avalanche, which is formed initially at the tip of the rod electrode with the highest electric field, and the effect of secondary ionization. Moreover, it is verified that the measured electron burst drift time with laser irradiation in the discharge gap is determined by the electric field of the discharge gap. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(2): 10–17, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10007

Interaction between a high-voltage circuit and an electrical discharge for laser applications

Numerical results concerning the interaction between a transverse electrical discharge and an external HV circuit in nitrogen are reported. The proposed model is based on a fluid description of the discharge plasma and on Poisson's law for the field calculation. This model includes secondary ionization effects and a study of the HV circuit behaviour by means of classical differential circuit equations. In particular, the influence of some circuit components on cathode region formation and on the discharge (pumping) current is studied. Results are reported for space and time variations of the electric field distribution, charged particle densities, net charge density and cathode sheath evolution. For a gap length of 1 cm and for 40 Torr, the cathode field reaches high values , the electron density is about and the cathode-oriented plasma front propagates towards the cathode with a velocity greater than . The maximum pumping current value (30 kA) is obtained in 5 ns and corresponds to a spark-gap inductance nH. The very fast growth of the pumping current is associated with the effective contribution of secondary ionization cathode effects.

Delta-electron emission in fast heavy ion atom collisions.

Biological damages such as mutations, chromosomal aberrations etc. are a consequence of biochemical changes mostly in the DNA. With ionizing radiation, these chemical changes are due to primary ionization events and secondary ionization effects caused by the primarily produced electrons. Differences in the biological response of densely ionizing radiation, like heavy charged particles, in comparison to sparsely ionizing radiation, such as X- or gamma-rays, are mainly due to the differences in the production of the so called delta-electrons. Therefore, the emission process of electrons i.e. the cross section for the primary ionization event as well as the energy and angular distribution of the emitted electrons should be understood in detail. The delta-electron emission processes occuring in fast heavy ion atom collisions are explained qualitatively. The different spectral structures of electron emission arising from either the target or the projectile are explained in terms of simple models of the kinetics of momentum transfer induced by the COULOMB forces. In collisions of very heavy ions with matter, high nuclear COULOMB forces are created. These forces lead to a strong polarization of the electronic states of the participated electrons. The effects of this polarization are discussed.

Modeling of electron-beam-controlled semiconductor switches

The subject of this paper is the mathematical modeling of a recently proposed class of electron-beam-controlled high-power semiconductor switches that are able to overcome the space-charge limitation of conventional electron bombarded semiconductor devices by utilizing the secondary ionization effects of cathodoluminiscence and bremsstrahlung. Current densities of several kA/cm2 at forward voltages some 10 V can be controlled with an electron beam of 100 keV and 1 A/cm2; holdoff voltages of more than 100 kV/cm and dark currents as small as 10 μA/cm2 are possible. The concept has several possible applications: Its fast and repetitive closing and opening under load makes it suitable for inductive energy storage applications; its linear characteristics suggests a use as a high-power modulation device.

Transient Development of Nanosecond Gas Discharges

The development of cufrent in gaseous spark gaps has been investigated in the context of a transmission-line pulse system. A simple model, which utilizes the electron continuity equation, provides a description of the formative period as well as the current buildup during the resistive phase. The E-field in the gap is assumed to be spatially uniform and dependent on time through temporal variations in the applied field. We have employed this simple model in analyzing the dependence of the formative time on the initial parameters of the discharge. At the end of the breakdown formation process, space-charge and secondary ionization effects become important. A two-dimensional time dependent model has been developed to include these effects. Current waveforms obtained from both models have been compared with experimental waveforms. Experimental measurements were performed in a 50-Ω pulse transmission-line system. Incident voltage waveforms of approximately rectangular shape were applied between large electrodes in a nitrogen filled test gap. Incident voltage and transmitted current waveforms were monitored with capacitive dividers and recorded by a fast transient digitizer.

Electrostatic Field Distribution and Breakdown Potential for a Hollow-electrode System in Rare Gases†

Abstract The values of the breakdown potential in both polarities of a system consisting of a ' hollow ' electrode formed by two parallel discs and a coaxial surrounding cylindrical electrode are measured in terms of the variable distance between the hollow electrode plates, at 0·1 mm Hg, 1 mm Hg, 2·5mm Hg and 5 mm Hg pressures in the rave gases He, Ne, A, Kr, Xe. In order to determine how far the geometrical and electrostatic field criteria may be used for explaining the polarity dependent breakdown asymmetries, one calculates the potential and field distribution of the investigated electrode system. The results agree with the hypothesis that photo-emissive secondary ionization effects are leading in the hollow-cathode discharge breakdown.