Threshold Breakdown Voltage Research Articles

Application of a Microstrip Gas Counter in Energy-Dispersive X-Ray Fluorescence Analysis

Performance characteristics of a microstrip gas counter operated as an x-ray fluorescence spectrometer are reported. Gas amplification as a function of microstrip anode–cathode voltage was measured, and the breakdown threshold voltage was determined in pure xenon. The detector temporal stability and the effect of gas purity were assessed. Energy resolution and linearity, detection efficiency and uniformity of spatial response in the 2–60 keV x-ray energy range were determined from the pulse-height distributions of the fluorescence x-ray spectra induced in a variety of single- and multi-element sample materials. Energy resolution similar to that of conventional proportional counters was achieved at 6 keV. © 1997 John Wiley & Sons, Ltd.

Impurity breakdown and electric-field-dependent luminescence in MBE and VPE GaAs layers

Impurity avalanche breakdown in n-type GaAs layers prepared by the LPE, VPE and MBE methods has been studied in detail using voltage-controlled current-voltage (I-V) characteristics and luminescence measurements together with computer simulations. Scholl's model of the first-order non-equilibrium phase transition in a two-level system was found to be adequate to describe the main experimental results. The threshold voltage for breakdown depends on the initial free-electron concentration. The hysteresis width diminishes with decreasing binding energy of electrons in the excited states of donors. The changes in luminescence spectra observed during impurity breakdown reflect changes in the charge state of shallow impurities. The band corresponding to D-A transitions disappears together with the decrease of the exciton radiative recombination rate. In the post-breakdown part of the I-V characteristics another region of nonlinear behaviour with hysteresis and sharp increase of instabilities was observed. Its origin has not yet been determined unambiguously.

Modeling capture, emission, and impact ionization of deep-level traps for Ga-As semi-insulating substrates

A numerical model that self-consistently computes electron capture, emission, and impact ionization from deep-level traps (DLTs) is presented. A GaAs n-i-n structure with the i-region representing the semi-insulating (SI) GaAs substrate is simulated using the model. It is found that the threshold voltage (defined as the onset voltage at which the leakage current begins to rise rapidly) for substrate breakdown may be dramatically reduced by the impact ionization of DLT trapped electrons. The temperature dependence of the threshold voltage may also be explained by the impact ionization effect. The model can improve the prediction of current-voltage characteristics of a deep-level-trap compensated semi-insulating GaAs substrate under the conditions of electric field and varying temperature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental Investigation of Axial Field Limitations in MHD Generators

Axial field breakdown in nonslagging wall, combustion-driven MHD generators was characterized by a rapid decline in axial voltage and a change in the mode of current transport from a relatively diffuse mode to a highly constricted and destructive mode. Cinephotographic records obtained for a simplified configuration demonstrated that breakdown could be initiated either in the plasma or in the interelectrode insulator. Breakdown resulted only when a threshold voltage was exceeded, with the voltage increasing with insulator gap size. For the electrode wall configuration studied, the threshold voltage for plasma-initiated breakdown was significantly higher than that for insulator-initiated breakdown. For the maximum voltages achieved in the full generator experiments, only insulator-initiated breakdowns were observed. No qualitative difference in anode and cathode wall breakdown behavior was observed. The threshold voltage for the generator configuration was lower than the value observed for the same insulator gap size in the simplified experiments; however, the qualitative features were similar.

Dual HCl Thin Gate Oxidation Process

The continued need for reliability and quality is inherent in the building of semiconductor devices. Control and reproducibility of the breakdown strength and threshold voltage of the gate oxide insulator is a basic and necessary condition for achieving these results. Alkali ions have been found to be a major cause of surface potential instabilities, and the removal of these mobile ion species is very important in the building of strong silicon dioxide insulators. in particular has been found to be an effective gettering agent when used in small percentages during a thermally grown oxidation process. Further work has been done on the treatment of oxides with a high temperature anneal step using small percentages of and after an initial oxide has been grown. This leads to the two‐step treatment or dual cycle. Using the dual cycle a 56% increase in electric field breakdown has been achieved over a standard one‐step oxidation cycle in rupturing the thin oxide under a 20,000 square mil capacitor. Decreased defect density seen on large capacitors will result in a significant improvement in VLSI manufacturing.

Characteristics of Edge Breakdowns on Teflon Samples

Geosynchronous satellites have been observed to exhibit anomalous behavior attributable to electrical discharges resulting from differential charging of satellite surfaces by energetic electrons. A program has been undertaken to study the characteristics of electrical discharges induced on silverbacked Teflon samples irradiated by a monoenergetic beam of electrons under carefully controlled laboratory conditions. Measurements of breakdown threshold voltages, particle emission and material damage have been made for Teflon samples (75 and 125μm thick) with selected edges exposed to the electron beam. Measurements indicate a strong dependence of threshold voltage upon the choice of sample edge that is exposed. The Teflon samples exhibit a difference of ~10kV in breakdown threshold voltage depending on the sample orientation. Optical birefringence indicative of long range alignment of the bulk material has been observed along axes which correspond to the axes that define the orientation for maximum and minimum threshold voltages. This result can be significant to spacecraft designers because optical prescreening of Teflon samples may allow optimal choice of material orientation upon the spacecraft to minimize the deleterious effect of dielectric discharges.

Experimental investigations of ionization growth in nitrogen. I

Thin gold film techniques and infinite plane-parallel electrode geometry have been used for precise measurements of ionization growth in molecular nitrogen over a range of values of E/p (60-2000 V cm-1 Torr-1) and p (0.5-60 Torr at 0 degrees C). With gold film as anode the transition from equilibrium to non-equilibrium ionization has been investigated and where possible new values for the primary and secondary ionization coefficients have been obtained. With gold film as cathode the total ionization is enhanced considerably at low values of E/p<or approximately=100 where decreases in threshold breakdown voltage as large as 1800 V have been noted. A variation of the secondary coefficient with electrode separation and a marked sensitivity to impurity in the gas sample have been observed. It is shown that this is consistent with secondary electron emission at the gold film by metastable (A3 Sigma u+) particles which diffuse to the boundary surface after production by electron impact excitation in the gas.

Properties of Gallium Arsenide Double-Injection Devices

The characteristics of identically fabricated double-injection devices made from oxygen-doped and chromium-doped bulk gallium arsenide are investigated. All these devices exhibit a current-controlled negative resistance once a threshold voltage is reached. The oxygen-doped devices and the thin chromium-doped devices (less than 3 mil) exhibit an abrupt current-controlled negative resistance followed by filamentary current conduction; this behavior is caused by double-injection transit-time effects. The thick chromium-doped devices (greater than 3 mil) exhibit a gradual, current-controlled negative resistance unaccompanied by filament formation; this behavior is due to excessive power dissipation resulting from high threshold voltages. The characteristics of the double-injection oxygen-doped devices show that a current saturation occurs in the prebreakdown region under certain conditions. The characteristics of the chromium-doped devices exhibit no such current saturation, only superlinear behavior. It is established that the oxygen devices have a threshold voltage for breakdown which is proportional to device length squared and that the chromium devices generally follow a similar law. Other evidence supporting the trapping barrier postulated by Lampert is also given. Filamentary conduction in the postbreakdown region is investigated by direct recording of the recombination radiation on infrared film. It is established that impedance variations and secondary breakdowns observed on the voltage-current characteristic are caused by movement of the filament position between the two injecting contacts. Filament position instabilities under cyclic excitation are observed and these effects are linked to a localized increase in the trapping barrier caused by heating along the filament site. Photographs of the recombination radiation emanating from both contacts establish the two-carrier nature of the postbreakdown filamentary state.