Single event induced charge transport modeling of GaAs MESFETs

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AbstradThe charge-collection processes of GaAs fieldeffect transistors are investigated as a function of the incident laser pulse energy via time-resolved chargecollection measurements and by two-dimensional computer simulation. The measurements and simulations reveal a feature that persists on a time scale of 100 ps, the amplitude of which varies strongly with the injected carrier density (pulse energy). The appearance of this feature is associated with a barrier lowering effect at the source/substrate junction, coupled with the drift-assisted transport of electrons through the substrate to the drain contact. This behavior is similar, but not identical to bipolar-gain models that have been suggested previously. We introduce the concept of iontrack segments and illustrate their utility in interrogating the complex mechanisms of charge collection and enhancement in GaAs FETs.Significant advances in our understanding of the charge-collection processes of GaAs FETs, and their role in single-event phenomena, have been achieved in recent years [l-161. The 1989 observation of charge collection in GaAs FETs in excess of that deposited by the ion [1,2], coupled with the measurement of anomalously low SEU thresholds for GaAs circuits [6], sparked a renewed interest in the charge-collection processes of these devices. Recently, the implementation of low-temperature grown (LT) GaAs buffer layers has been found to inhibit charge-enhancement process in GaAs devices [ll-151, leading to a significant reduction in their SEU susceptibility [ 171. The LT GaAs results, in particular, illustrate that enhanced charge collection is a primary contributor to the very poor SEU performance of non-LT GaAs FET-based ICs.Despite the recent advances in our understanding of charge-collection in GaAs devices, much remains to be understood about the complex physics of the charge-collection process and its relationship to SEU. In this paper we present picosecond time-resolved charge-collection measurements and computer simulation results that provide new insight into the chargeenhancement processes in GaAs FETs. Both experiment and simulation reveal a feature that persists on a one-hundred picosecond time scale, the amplitude of which exhibits a sensitive dependence on the injected carrier density. The simulation results indicate that this feature is associated with a charge-enhancement process in which carriers are transported from source to drain deep through the substrate of the device, The characteristics of this process appear similar to, but not identical with, bipolar-gain models previously suggested in the literature. II. EXPERIMENTALLaser-induced charge-collection measurements were performed with nominally 1 ps duration optical pulses centered at 605 nm ( N 2 eV) at a pulse repetition rate of 1 kHz. The optical pulses are focused onto the DUT with a 100 x microscope objective, resulting in a measured Gaussian spot size of 1.2 pm at the surface of the DUT. For all of the experiments reported here the laser spot is focused between the gate...

Section: Resultsmentioning

confidence: 85%

Charge-enhancement mechanisms of GaAs field-effect transistors: Experiment and simulation

McMorrow

Melinger

Knudson

et al. 1998

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“…The soft error issue was unresolved and required additional investigation [69]. SRAM soft error tests [70], [71] and charge collection experiments [72], [73], with the help of device simulation tools [74], determined that the SEE sensitivity was related to several items: 1) the uninsulated GaAs FET gate; 2) hole collection in the semi-insulating substrate that provided a mechanism to induce a bipolar transistor effect [73] or back-gate [74]; and 3) the low-doped substrate that provided long diffusion lengths, which increased collection volumes. Also, as noted in Table I, the ionization in GaAs per unit length is higher than that of silicon.…”

Section: Radiation Effects In the 1990smentioning

confidence: 99%

“…It was not until techniques were developed to reduce lifetimes in the GaAs substrate that the soft error issue was mitigated [74]. Doping the GaAs substrate would degrade isolation.…”

Section: Radiation Effects In the 1990smentioning

confidence: 99%

Historical perspective on radiation effects in III-V devices

Weatherford

Anderson²

2003

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“…The back-channel turn-on mechanism depends in a sensitive fashion on the device bias conditions. Both experiment [2-41 and computer simulation [5] results suggest that the carriers deposited in the substrate by the ion induce a loss of gate control of the device. This is a field-effect phenomenon that is intrinsic to FET devices.…”

Section: Introductionmentioning

confidence: 99%

Charge-collection mechanisms of heterostructure FETs

McMorrow

Melinger

Thantu

et al. 1994

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Ion-and laser-induced charge-collection transients measured for AlGaAs/InGaAs heterostructure insulated-gate field-effect transistors (HIGFETs) reveal evidence for two mechanisms of enhanced charge collect ion: a channel-modulation mechanism that dominates the chargecollection processes at positive gate biases and can persist for several nanoseconds; and a parasitic bipolar transistor mechanism that shows a sensitive dependence on the density of free carriers injected into the device, and is complete within a few hundred picoseconds. The results reinforce the utility of the laser technique for investigating the charge-collection mechanisms of semiconductor devices. I. IntroductionRecent work has focused on characterizing the SEU performance [1,2] and basic chargecollection mechanisms [2-41 of GaAs MESFETbased integrated circuits. Picosecond time-resolved charge-collection measurements [3,4], coupled with time-integrated (charge-sensitive preamplifier) measurements and computer simulations [5], provide an accurate picture of the mechanisms of charge collection and charge enhancement in MESFETs. It is now generally accepted that while MESFET based circuitry is well suited for high total-dose and high dose-rate environments, the very large SEU susceptibility of MESFET-based digital ICs limit their applicability for most space-based applications.Complementary het eros t ruct ure insulatedgate field-effect transistor (C-HIGFET) technology represents a low-power alternative to MESFET technology that maintains the high speed and total dose immunity of GaAs that is required for space-based digit a1 applications. Recent studies [6,7] reveal that C-HIGFET technology exhibits SEU performance superior to that of GaAs MESFETs. In this paper we examine the charge-collection mechanisms of nchannel HIGFET test structures. Our results reveal that the charge-collection dynamics of HIGFETs for times less than 1 ns are remarkably similar to those of GaAs MESFETs. Bias-dependent and laser pulse energy dependent measurements suggest further that the mechanisms of charge collection are also similar, and reveal clear evidence for charge enhancement effects analogous to those observed for MESFETs. These results are consistent with the