Forward Current Pulse Research Articles

Reversible Total Ionizing Dose Effects in NiO/Ga2O3 Heterojunction Rectifiers

NiO/Ga2O3 heterojunction rectifiers were exposed to 1Mrad fluences of Co-60 g-rays either with or without reverse biases. While there is small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma-photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000x reduction in forward current and 100x increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on-off ratio is also reduced by almost 5 orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of < 4 cm-1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current-voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes. Figure 1

Reversible Total Ionizing Dose Effects in NiO/Ga2O3 Heterojunction Rectifiers

NiO/Ga2O3 heterojunction rectifiers were exposed to 1Mrad fluences of Co-60 g-rays either with or without reverse biases. While there is small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma-photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000x reduction in forward current and 100x increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on-off ratio is also reduced by almost 5 orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of < 4 cm-1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current-voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes.

Reversible total ionizing dose effects in NiO/Ga2O3 heterojunction rectifiers

NiO/Ga2O3 heterojunction rectifiers were exposed to 1 Mrad fluences of Co-60 γ-rays either with or without reverse biases. While there is a small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000× reduction in forward current and a 100× increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on–off ratio is also reduced by almost five orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of &amp;lt;4 cm−1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current–voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate that these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes.

Impact of High-Energy Electron Irradiation on Surge Currents in 4H-SiC JBS Schottky Diodes

The effect of irradiation with high-energy (0.9 MeV) electrons on surge currents in high-voltage (operating voltage 1700 V) 4H -SiC Schottky p-n diodes is studied in the microsecond range of the forward-current pulse duration. With increasing irradiation dose Φ, the hole injection threshold steadily grows, and the base-modulation level by minority carriers (holes) becomes lower. At Φ = 1.5 × 1016 cm–2, no hole injection is observed up to forward voltages of ~30 V and forward current densities of j ≈ 9000 A/cm2.

Влияние облучения электронами высокой энергии на характеристики ударных токов высоковольтных интегрированных 4H-SiC p-n-диодов Шоттки

The effect of high energy (0.9 MeV) electron irradiation on surge currents of high-voltage 4H-SiC JBS was investigated in the microsecond range of the forward current pulses duration. With irradiation dose  growth, the threshold of hole injection monotonically increases, and the base modulation level by minority carriers (holes) decreases. At = 1.5×1016 cm-2, the hole injection is not observed up to forward voltage values of ~ 30 V and forward current density j  9000 A/cm2.

Investigation of Reverse Switch-On Dynistors Upgraded for Reducing the Energy Loss when Switching Reverse-Current Pulses

The results of investigations of new semiconductor devices, reverse switch-on dynistors dynistors–diodes (RSDDs), with an operating voltage of 2 kV and a 50-mm diameter of the structure are presented. Their comparison with conventional RSDs shows that the losses in RSDDs are approximately 2 times lower when high-power reverse-current pulses are switched, the losses are virtually the same during switching, and the losses are 15–20% higher when switching rapidly rising forward-current pulses. The limiting abilities of RSDDs are determined when switching unipolar current pulses with a duration of 300 μs: 30 and 100 kA in the reverse and forward directions, respectively. The possibility of reliable switching of alternating slowly damped current pulses with a duration of 40 μs and amplitudes of the first forward and reverse half-waves of 90 and 65 kA, respectively, with which conventional RSDs cannot operate, is shown.

Electrical Performance of 4H-SiC Based Drift Step Recovery Diodes

Mesa-epitaxial 4H-SiC p+-p-no-n+-diodes were fabricated from commercial epitaxial wafers. Reverse recovery characteristics of the diodes were measured in pulse regimes to be relevant to operation of drift step recovery diodes (DSRDs) [1]. When injecting the minority carriers by forward current pulse followed by applying a reverse voltage pulse, the diodes are able to break the reverse current in a subnanosecond time (DSRD-mode). Different regimes of diode operation in DSRD-mode are investigated such as variable reverse voltage amplitude, forward current amplitude and duration, time delay between forward and reverse pulses.

Dynamic characteristics of 4H-SiC drift step recovery diodes

The dynamic characteristics of 4H-SiC p+–p–n0–n+ diodes are experimentally studied in the pulsed modes characteristic of the operation of drift step recovery diodes (DSRD-mode). The effect of the subnanosecond termination of the reverse current maintained by electron-hole plasma preliminarily pumped by a forward current pulse is analyzed in detail. The influence exerted on the DSRD effect by the amplitude of reverse-voltage pulses, the amplitude and duration of forward-current pulses, and the time delay between the forward and reverse pulses is demonstrated and accounted for.

Subnanosecond Semiconductor Opening Switch Based on 4H-SiC Junction Diode

Mesa-epitaxial 4H-SiC p+-p-no-n+-diodes were fabricated and their reverse recovery characteristics were measured in pulse regimes to be relevant to DSRD- and SOS-modes of operation [I.V. Grekhov, G.A. Mesyats, Physical basis for high-power semiconductor nanosecond opening switches, IEEE Transactions on Plasma Science 28 (2000) 1540-1544]. It has been found that after short pumping the diodes by forward current pulse (5-ns duration, 200-A/cm2 peak current density) followed by applying the reverse voltage pulse (rise time 2 ns) the diodes are able to interrupt the reverse current density of 3.5 - 25 kA/cm2 in a time less than 0.3 ns.

A High Color Rendering Index on Multichip LED Light Source

Light source carrying a high color rendering index (CRI) finds potential applications in people’s everyday life as well as lighting industry. Combination of multi-wavelength LED light sources with designated direct emission sources can achieve warm-white and cool-white light. A generic design of high CRI multi-wavelength light-emitting-diode (LED) light source, using flyback converter, pulse width modulation (PWM) voltage control, variable resistor, and timer, is proposed. The PWM pulse is for the voltage control of cascade LEDs, while variable resistor manipulates the current flowing through LEDs. A design of dimming drive with cascade-connected electronic switch is also proposed. By adjusting the width of the dimming signal, the average value of forward current pulse can be changed, and therefore the objective, the tuning of the amount of light output, can be fulfilled. The advantage of the proposed design is its short response time.

Features of degradation in high-voltage 4H-SiC p-i-n diodes under the action of forward current pulses

Degradation in silicon carbide based p-i-n diodes under the action of a forward current in a pulsed regime has been studied for the first time. It is established that, at current pulse durations below several milliseconds, the extent of degradation is much smaller than that in the dc regime for the same total charge transferred through the diode structure. The partial self-recovery (decrease in the extent of degradation with the time) of the diode structures at room temperature was also observed for the first time.

Observation of a long-range electric drift of negatively charged vacancies in the space-charge regions of Au/n-Si Schottky diodes

In-depth distributions of PsV and CiPs complexes formed in the space-charge regions of Au/n-Si Schottky diodes irradiated with fast electrons in a special electrical regime have been investigated. In the course of the irradiation the diodes were periodically driven into the reverse-bias state with square-shaped voltage pulses of fixed amplitude alternating with the forward-current pulses at a 2 MHz frequency. Non-flat profiles of PsV concentration have been revealed by deep-level transient spectroscopy measurements, while the interstitial defects been revealed by deep-level transient spectroscopy were found to have a constant density. The result is regarded as strong evidence for the long-range (approximately 0.1-1 mu m) field-assisted drift of negatively charged vacancies (V-) across the depleted region. The diffusion length of V- evaluated from the drift model (about (3.8+or-0.4)*10-2 mu m for the float-zone silicon used with a phosphorus content of 5*1015 cm-3) was found to be consistent with the value expected from the theory of diffusion-limited reactions.

Time Resolved Electroluminescence in a-Si:H p-i-n Junctions

ABSTRACTTime resolved and steady state electrololuminescence (EL) measurements have been performed in a-Si:H p-i-n junctions at 10K &lt; T &lt; 300K in order to study the recombination in these devices. At low temperatures the rise of the EL following a rectangular forward current pulse consists of a fast component with a time constant of a few μs and a slow component with a time constant of about a ms. The data suggest that the time response of the EL is determined not only by the recombination but also by the time to build up the carrier density for bimolecular radiative recombination. The fast component of the EL is attributed to the field enhanced recombination of carriers which survived from the preceding pulse. Steady state measurements reveal characteristics of bimolecular recombination. The EL spectrum is shifted by 50meV to lower energies with respect to the photoluminescence spectrum.

Recombination in germanium: Voltage-decay experiments on induced-junction devices and validity of the SRH model

Measurements of open-circuit voltage decay following the application of a dark forward-current pulse have been made on induced pn-junction devices in moderately-doped germanium. Minority-carrier lifetime has been measured over a wide temperature range, as well as over a wide range of injection level. All of the results are accurately explained by the SRH model with a single acceptorlike trap level at an energy 0.128 ± 0.008 eV below the conduction band edge, i.e. above the equilibrium Fermi level in the n-type material. The dependence of the hole capture cross section on temperature is further quantitatively explained by the theory for coulombic capture of Rose, without adjustable parameters.

A comparison of gamma-irradiation-induced degradation in amphoterically Si-doped GaAs LED's and Zn-diffused GaAs LED's

A comparison is presented of the effects of gamma irradiation on the properties of amphoterically Si-doped GaAs LED's and Zn-diffused GaAs LED's. It is shown that the light output of GaAs:Si LED's is severely degraded by irradiation, and, in addition, that the light output cannot be recovered through forward-bias-induced annealing. In contrast, commercially available dome-shaped GaAs:Zn emitters with comparable power outputs degrade much less, and the degradation that is observed can be recovered by forward-bias-induced annealing. Further, this bias-induced recovery can be achieved by applying forward-current pulses only 10 to 50 ms in width. The lack of any bias-induced recovery in the GaAs:Si devices led to an investigation of gamma-induced deep levels using the transient capacitance method of deep level transient spectroscopy (DLTS). Following irradiation, two levels with thermal activation energies of 0.21 and 0.78 eV were observed. Subsequent forward bias reduced the concentration of the 0.21-eV level but had relatively little effect on the 0.78-eV level. These results suggest that the near midgap 0.78-eV level is one of the nonradiative recombination centers responsible for light output degradation.

Advanced apparatus for the evaluation of stored charge and carrier lifetime in semiconductor devices

The apparatus described allows the stored charge in a diode from the reverse recovery behaviour to be measured. It permits an adjustable time delay between the end of the forward current pulse and the application of reverse bias. The amount of charge recombined during the delay interval may be evaluated easily and a lifetime determined. For convenience, a digital integrator and programmer has been developed, allowing an easy and accurate valuation of the stored charge.

Consequent Arc Backs and Consequent Arc Throughs in HV Mercury-Arc Valves

This paper traces developments in high-voltage mercury arc valves for HVDC power transmission in relation to problems conceming "consequent" failure. Investigations are reported on the physical conditions in valves during and after high forward current pulses. An account is given of some of the main development work aimed at producing valves with greatly reduced consequent failure probability.

Behavior of thyristors under transient conditions

The capability of gate-triggered thyristors to withstand steep wavefront, high-current pulses (i.e., di/dt capability) is a function of both junction temperature and frequency of operation. Localized internal heating occurs during turn-on and may lead to thermal runaway. The conditions required for this to occur have been determined by destructively testing many devices. The initial conducting area of a thyristor largely determines di/dt capability, which is not necessarily related to the size of the device but is a function of the design of the gate region. Gate drive is very important for determining the di/dt capability of a thyristor having a conventional gate design. Two devices which have been designed to increase the initial conducting area are discussed. One of these devices, if improperly designed, can lose its effectiveness with high gate drive. This characteristic can be studied by observing the reverse recovery current immediately following short forward current pulses.