Fine structure and electromagnetic radiation in second breakdown

Thermal phenomena have been suggested as the initiating mechanisms for second breakdown in transistors. The experiments described below examine certain electrical and optical effects associated with second breakdown in order to determine if thermal effects can be held primarily responsible. In studying the open-base behavior of several types of devices, it was observed that second breakdown was followed by additional discontinuities at higher current levels, all similar to second breakdown in their electrical behavior. Simultaneously with the appearance of a voltage discontinuity, light was emitted by the device. The light output level generally increased monotonically with increasing collector current except when a voltage discontinuity occurred, at which time a discontinuous increase in the light output level also occurred. The spectral distribution of the emitted light was examined and found to be similar to the distribution from a single junction biased into avalanche. The results of the electrical measurements strongly suggest the existence of a number of interacting sites capable of sustaining second breakdown. The optical measurements indicate that the characteristics of a transistor in second breakdown are not purely thermal in nature, but that a plasma effect may be associated with a device exhibiting an anomalous breakdown.     

Effect of ionizing radiation on MOS capacitors

A numerical model of metal-oxide-semiconductor (MOS) capacitor has been developed to investigate the effect of ionizing radiation on the characteristics of the device during exposure and also in the post-irradiated condition. The model takes into account the effect of radiation-induced changes in silicon-dioxide as well as in silicon substrate of MOS structure. It is found that the total high frequency capacitance of the device during exposure to radiation is different from its value in the post-irradiated condition. The results of the study are expected to be useful in predicting the behavior of MOS based devices operating in radiation environment.     

The effect of ionizing radiation on the breakdown of large gaps in air

The influence of gamma radiation on the breakdown of a point-plane gap has been studied using impulse voltages of short and long wavefronts. Scatter of breakdown of some gaps is reduced by a factor of two and the mean breakdown value is reduced by a few percent.     

Emission of visible radiation from extended plasmas in silicon diodes during second breakdown

Thin film silicon-on-sapphire diodes have been reverse biased into second breakdown and the formation of a filament has been observed between the anode and cathode. This filamentary conduction was accompanied by emission of visible radiation, the light being much more intense than that associated with avalanche or microplasma emission. The filamentary emission appeared to be associated with both thermal heating of the diode to temperatures as hot as 600-800°C and the formation of a plasma. Quantum efficiencies as high as 0.04 percent have been observed and plasmas extending over anode-cathode spacings of up to 100 µm have been observed.     

A survey of second breakdown

The existence of a "new high-current mode of transistor operation," now generally known as second breakdown, was first reported by Thornton and Simmons in 1958 and was used to explain the mysterious failures that were observed to occur under certain operating conditions. Since then, with the production of higher power and higher frequency transistors, the problems resulting from the existence of second breakdown have proliferated. Interest in the phenomenon has grown concurrently and many papers about second breakdown can be found in the literature. These papers cover a range of interest that extends from theoretical studies of the basic mechanisms involved to interpretations of specifications for transistor operation free of second breakdown. A complete understanding of second breakdown has not yet been achieved and several concepts of second breakdown prevail. The purpose of this paper is to review historically the work that has been reported in order to present a coherent and comprehensive picture of the present status of second breakdown.     

Effects of ionizing radiation on glow discharge detectors

Glow discharge detectors in the abnormal glow mode can be used as sensitive detectors of microwave and millimeter wave radiation even in the presence of very intense γ ionizing radiation fields where semiconductor devices cannot operate. In the subnormal glow mode, glow discharge detectors give promise of being able to monitor ionizing radiation fields so intense that the usual electronic detectors saturate.     

A graded-gap detector of ionizing radiation

The current response of Al_xGa_1−x As graded-gap layers to optical and X-ray radiation was studied. A graded-gap electric field in the 15-μm-thick Al_xGa_1−x As layers, with x varying from 0 to 0.4, ensures the complete collection of charges generated by ionizing radiation and makes it possible to attain the value of 0.25 A/W for the current-power sensitivity of Al_xGa_1−x As. In the layers with a lowered doping level of the narrow-gap region of the graded-gap Al_xGa_1−x As layer, the voltage-power sensitivity to X-ray radiation with energy lower than 15 keV is as high as 1.6×10³ V/W in the photovoltaic mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 124–128. Original Russian Text Copyright ? 2002 by J. Požela, K. Požela, Šilėnas, Jasutis, Dapkus, Kinduris, Jucienė.     

The impact of total ionizing radiation on body effect

A new phenomenon, for the first time, shows that radiation-induced body effect factor decrease in NMOS transistors is presented. The results indicate that body effect factor shift decreases as the total ionizing dose (TID) level increases in NMOS transistors, especially in the narrow-channel ones, which can be considered as one of the radiation-induced narrow-channel effect (RINCE). A first-order model is developed by applying charge conservation principle. Good agreement is obtained by comparing the modeling with experimental results. Finally, some implications to mitigate the RINCE effect are discussed.     

Preliminary ionizing radiation tests on n-channel inversion-mode GaInAs MISFET's

Preliminary results of low-dose rate ionizing radiation (cobalt-60) tests on n-channel inversion-mode GaInAs MISFET's up to a total dose of 5 × 10⁷rad(Si) are presented. The data show that the GaInAs MISFET threshold voltage shifts negatively up to a total dose of 5 × 10⁵rad(Si), with a maximum shift of -0.9 V. The threshold voltage then shifts in a positive direction at higher doses. The mobility factor decreases very slightly and then increases with increasing dose.     

Avalanche injection and second breakdown in transistors

A rapid type of second breakdown observed in silicon n⁺-p-n-n⁺transistors is shown to be due to avalanche injection at the collector n-n⁺junction. Localized thermal effects, which are usually associated With second breakdown, are shown to play a minor role in the initiation of the transition to the low voltage state. A useful tool in the analysis of avalanche injection is the n⁺-n-n⁺diode, which exhibits negative resistance at a critical voltage and current. A close correspondence between the behavior of the diode and the transistor (open base) is established both theoretically and experimentally. Qualitative agreement with the proposed model is obtained for both directions of base current flow. It is shown that transistors having thin, lightly doped collector regions are particularly susceptible to avalanche injection, which suggests that some compromise may be necessary in the design of high-frequency power transistors.     

Electrical and structural effects on ionizing radiation in IGFETS

In terms of initial device yield, and long term reliability, process induced radiation damage represents an area of considerable concern. The processes that need to be examined include Ion Implantation, X-ray, E-Beam and Ion Beam lithography, Electron Beam metal evaporation, Sputtering, Reactive Ion Etching, and even SEM examination. The paper discusses the effects of synchrotron X-radiation in the energy range 300-100 eV, as well as Al Ka exposures which simulate the effective wavelength of storage rings planned for X-ray lithography. It will describe such effects in the context of preliminary studies dealing with varying rad exposure level at constant gate insulator thickness, as well as the behavior at several rad exposure levels as a function of gate insulator thickness. Data will be presented indicating that despite prevailing beliefs, damage in the synchrotron range follows a linear relationship over the thickness range from less than 10 nm to 50 nm, indicating strongly that damage resides near the interface and is constant with increasing insulator thickness. It will be shown that such behavior is consistent with a simple model. Even if such damage can be annealed completely using normal techniques, which is questionable, there are wide-ranging implications concerning the rad hardness of scaled devices.     

Improved second breakdown of integrated bipolar power transistors

This paper presents two new power bipolar transistor structures With greatly increased forward Second breakdown values without saturation voltage degradation. These structures, labeledS1 andS2, were obtained with slight modification of the output stages of an IC power amplifier and without complicating the standard IC process. The design concepts developed in this paper were applied to power transistors fabricated using two different processes already in production: processA(V_{CEO(sus)} gt 50V) and processB(V_{CEO(sus)} gt 80V). Measurements have Shown that an improvement of three times for dc conditions and four times or more for single pulses duration of less than 1 ms can be obtained for structureS1 while structureS2 is able to achieve the proportionality between power silicon area and power levels. Experimental temperature distributions over emitter area and some theoretical calculations for the steady-state condition are given.     

A graded-gap photoelectric detector for ionizing radiation

A heterostructure consisting of a graded-gap p-Al_xGa_1?xAs layer on an n-GaAs substrate is studied in relation to its role as a photoelectric-response detector of X-ray photons and α particles. It is found that the current-power sensitivity of the detector is as high as 0.13 A/W and the voltage-power sensitivity exceeds 10⁶ V/W. The effect of preliminary irradiation with 5.48-MeV α particles (²⁴¹Am) on the detector’s sensitivity is studied. It is established that the detector’s sensitivity is reduced by a factor of 1.5–2 after irradiation with α particles at a dose of 5 × 10⁹ cm^?2. A further increase in the radiation dose to 4 × 10¹⁰ cm^?2 does not affect the detector’s sensitivity.     

Current mode second breakdown in epitaxial planar transistors

Current mode second breakdown is a type of voltage "switchback" observed in epitaxial transistors. The phenomenon is initiated when the emitter is injecting at a collector voltage in excess of the collector-emitter sustaining voltage, and is characterized by delay and voltage fall times on the order of a nanosecond. The device can be sustained in the low voltage state only as long as there is sufficient charge to produce conductivity modulation within the collector-base depletion region. When the available charge is exhausted, the collector voltage will recharge at a rate determined by the external circuit. At some critical current density, the collector-base depletion region collapses toward the high conductivity substrate. The electric field within the depletion region increases as the depletion region width narrows, until avalanche occurs. The sustaining voltage will be determined by the bulk base-to-collector avalanche voltage. A consequence of this behavior is that most epitaxial transistors cannot operate stably in the LVCERmode, and switching-off unclamped inductive circuits with the emitter-base junction terminated in some finite resistance will lead to second breakdown.     

Modeling of ionizing radiation effect on optoelectronic-integrated devices (OEIDs)

The ionizing radiation effect on the static and dynamic behavior of an optoelectronic-integrated device composed of a hetrojunction phototransistor and light-emitting diode is studied theoretically. First, the device characteristics before irradiation are investigated based on the equivalent circuit of the constituent devices and the optical feedback inside the device. Second, the effect of neutron irradiation flux on transient behavior of this device is theoretically studied. It was noticed that, the neutron irradiation flux reduces the transient response in both the amplification and switching modes. Also, neutron irradiation flux increases the switching voltage of the device and decreases the output current, this means that the ON state device which exposed to this irradiation flux will turn to the OFF state because it will need higher value of switching voltage. Either increasing the amount of input light or the applied voltage is required to turn the device to the ON state again. This type of models can be exploited as optical amplifier, optical switching device and other applications.     

Effects of ionizing radiation on oxidized silicon surfaces and planar devices

This paper examines in detail the effects of high and low energy electron, X-ray, and ultraviolet radiation on oxidized silicon surfaces and planar devices. Two permanent effects of ionizing radiation on oxidized silicon surfaces are distinguished: 1) The buildup of a positive space charge within the oxide, and 2) The creation of fast surface states at the oxide-silicon interface resulting in increased surface recombination velocity. The dependence of these effects on dose and dose rate, on bias applied during irradiation, and on structural parameters is discussed and a theory is presented which accounts for the observed features of the space-charge buildup. This theory involves trapping of holes which are generated within the oxide by the radiation. It is shown that all details of the experimental observations can be accounted for by assuming a high density of hole traps near the oxide-silicon interface which decays rapidly with distance into the oxide. Radiation-induced changes in the characteristics of MOS and junction field-effect transistors, p-n junction diodes, and p-n-p and n-p-n transistors are reported and examined in terms of the above two effects. It is shown that the charge buildup causes shifts in the operating point of MOS transistors, catastrophic increases in the reverse current of p-n junctions, and variations in their breakdown voltage. The increase in fast surface-state density is responsible for the lowering of the transconductance of MOS transistors and, in combination with the space-charge buildup, for the degradation of the current gain in bipolar transistors. It is shown that junction field-effect transistors are relatively insensitive to both effects of ionizing radiation and therefore offer the most promise for use in ionizing radiation environments.     

Effect of ionizing radiation on the sensitivity to hormonal inducers of differentiation in induced mammary cancer in rats

gamma-Irradiated rat mammary tumours induced by DMBA are likely to enhance the level of differentiation and to lose their malignant properties when stimulated to differentiation by neuroendocrine factors.