Charge-collection mechanisms of heterostructure FETs

Abstract

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

Radiation Effects in Iii-v Semiconductor Electronics

“…10a, drain charge-collection transients are plotted as a function of gate bias for a GaAs n-channel HFET for excitation by 1 ps 610 nm optical pulses focused between the gate and drain electrodes. 86 Similar results are observed for several different types of GaAs FETs, 85 ' 95 ' 97 ' 99 and for alpha particle irradiation 86 These data illustrate the dependence on gate bias of the three components noted above. In particular, when the device is biased strongly "off (pinch-off for this device is at a gate bias of approximately 0.15 V) contributions from components (b) and (c) are suppressed.…”

“…10b shows charge-collection transients for a n-channel GaAs HFET measured as a function of the injected carrier density. 86 These results provide insight into the physical origin of component (b), which typically exhibits a delayed maximum and decays on a time scale of a few hundred picoseconds. As is evident, component (b) becomes quite prominent at the higher pulse energies, while its contribution is negligible at the lowest pulse energy.…”

Charge-collection characteristics of GaAs heterostructure FETs fabricated with a low-temperature grown GaAs buffer layer

“…4 and 5 is reminiscent of similar behavior observed for conventional MESFET and HIGFET devices [10,11], and is consistent with charge-enhancement occurring via a backchannel-modulation mechanism. When the device is biased near pinch off, the charge deposited in the 0.3 prn region above the LT GaAs buffer layer is sufficient to modulate the channel conductivity.…”

“…Ion and laser-induced chargecollection measurements were performed with the NRL ion microbeam facility and the ultrafast laser facility, respectively, which have been described in detail elsewhere [5,11,21]. The laser experiments were performed with nominally 1 ps; duration optical pulses centered at 602 nm ( N 2 eV) at a pulse repetition rate of 1 KHz.…”