T. N. Fogarty

dc and rf performance of proton-irradiated AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) with a range of gate lengths (0.8–1.2 μm) and widths (100–200 μm) were exposed to 40 MeV protons at fluences of 5×109 or 5×1010 cm−2. The drain–source currents in the devices decreased by 15%–20% at the higher fluence, while the extrinsic transconductance decreased by ∼30% under the same conditions. Based on the increases in the reverse breakdown voltage and the channel resistance, the main degradation mechanism is believed to be creation of deep trap states in the band gap which remove electrons from the channel. The maximum frequency of oscillation, fMAX, also decreased as a result of the proton-induced damage, with a change of −20% at the shorter gate widths and −50% at the largest widths. The reverse recovery switching time was essentially unaffected by the irradiation, remaining at ∼1.6×10−8 s. Postradiation annealing at 800 °C was successful in restoring the dc and rf performance parameters to ⩾90% of their original values. The AlGaN/GaN HEMTs are...

High energy proton irradiation effects on SiC Schottky rectifiers

4H-SiC Schottky rectifiers with dielectric overlap edge termination were exposed to 40 MeV protons at fluences from 5×107–5×109 cm−2. The reverse breakdown voltage decreased from ∼500 V in unirradiated devices to ∼−450 V after the highest proton dose. The reverse leakage current at −250 V was approximately doubled under these conditions. The forward current at −2 V decreased by ∼1% (fluence of 5×107 cm−2) to ∼42% (fluence of 5×109 cm−2), while the current at lower biases was increased due to the introduction of defect centers. The ideality factor, on-state resistance, and forward turn-on voltage showed modest increases for fluences of ⩽5×108 cm−2, but were more strongly affected (increase of 40%–75%) at the highest dose employed.

Proton irradiation of MgO- or Sc2O3 passivated AlGaN/GaN high electron mobility transistors

Abstract AlGaN/GaN high electron mobility transistors with either MgO or Sc 2 O 3 surface passivation were irradiated with 40 MeV protons at a dose of 5×10 9 cm −2 . While both forward and reverse bias current were decreased in the devices as a result of decreases in channel doping and introduction of generation–recombination centers, there was no significant change observed in gate lag measurements. By sharp contrast, unpassivated devices showed significant decreases in drain current under pulsed conditions for the same proton dose. These results show the effectiveness of the oxide passivation in mitigating the effects of surface states present in the as-grown structures and also of surface traps created by the proton irradiation.

Effects of high-dose 40 MeV proton irradiation on the electroluminescent and electrical performance of InGaN light-emitting diodes

InGaN multi-quantum-well light-emitting diodes (LEDs) in the form of unpackaged die with emission wavelengths from 410 to 525nm were irradiated with 40MeV protons to doses of 5×109–5×1010cm−2. The highest dose is equivalent to more than 100 years in low-earth orbit. The projected range of these protons is >50μm in GaN and thus they traverse the entire active region. The electroluminescent intensity from the LEDs decreased by only 15%–25% even for the highest doses and the reverse breakdown voltage increased by 1–2V from their control values of ∼21–29V. The percentage change in breakdown voltage and electroluminescence intensity was independent of the initial emission wavelength over the range investigated, within experimental error. The GaN LEDs exhibit extremely good stability to these high-energy proton irradiations with no measurable change in contact resistance or contact morphology.

Effect of high-energy proton irradiation on DC characteristics and current collapse in MgO and Sc2O3 passivated AlGaN/GaN HEMTs

MgO or Sc 2 O 3 passivated AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated with 40 MeV protons at a dose equivalent to ∼10 years in low-earth orbit. Very little change in drain-source current, transconductance, or diode ideality factor was observed under these conditions, but the reverse breakdown increased due to a decrease in channel electron density. In addition, no significant change was observed in the drain-source current under pulsed conditions, indicating that the proton irradiation did not alter the effectiveness of the MgO and Sc 2 O 3 in passivating surface states.

Atomic-scale processes involved in long-term changes in the density of states distribution at the Si/SiO2 interface

We utilize very sensitive magnetic resonance measurements to observe changes in the densities of interface trap centers hundreds of hours after irradiation. Our observations provide direct atomic-scale evidence for slow changes in Si/SiO2 interface-state density distributions which appear after the devices have been damaged. Our observations also explain (at least in part) why different groups report somewhat different shapes for the density of interface states in the silicon band gap.

Ionization and displacement damage irradiation studies of quantum devices: resonant tunneling diodes and two-dimensional electron gas transistors

The radiation tolerance of two quantum devices, InP-based resonant tunneling diodes (RTD) and GaAs based two-dimensional electron gas transistors (2-DEGT), was investigated with ionizing and displacement damage radiation. The RTDs were subject to a maximum total gamma dose of 1 Mrad(InP), 55 MeV protons to a fluence of 3.5/spl times/10/sup 11/ cm/sup -2/, high energy neutrons to a fluence of 5/spl times/10/sup 10/ cm/sup -2/ and heavy ions with a maximum LET (InP) of 23.6 MeV-cm/sup -2//mg to a fluence of 1/spl times/10/sup 7/ cm/sup -2/. Using the peak-to-valley current ratios as the figure of merit, no radiation effects were detected on the RTDs measured under these circumstances. The 2-DEGTs were irradiated to a total gamma dose of 50 krad(GaAs) and 55 MeV protons to a fluence of 5/spl times/10/sup 10/ cm/sup -2/. Under gamma irradiation, a reduction in transconductance was observed, while the proton irradiated devices show an enhancement in the transconductance. The magnitude of these effects was proportional to gamma dose and proton fluence respectively. The effects are transient. For the gamma exposure, the tested 2-DEGTs almost completely recovered their pre-radiation performance. However, the proton-irradiated devices only recovered about half-way to their pre-irradiated characteristics. The transient times were on order of hours and may indicate annealing effects.

Proton and Gamma-Ray Irradiation Effects on InGaP/GaAs Heterojunction Bipolar Transistors

Large-area (75 μm emitter diameter) InGaP/GaAs heterojunction bipolar transistors (HBTs) were irradiated either with 40 MeV protons at fluences up to 5 × 10 9 cm -2 or with Co 60 γ-rays to maximum doses of 500 Mrad. Both types of radiation produced increases in generation-recombination leakage current in the emitter-base junction The dc current gain of the HBTs decreased monotonically with increasing γ-ray dose, hut was found to increase slightly for proton irradiation due to differential changes in the base and collector resistances. The HBTs appear to be well-suited to space or nuclear industry applications.

Application of radiation sources to simulate the radiation environment in low earth orbit: results on optoelectronic devices for International Space Station

Abstract There is a trend toward evaluating the space worthiness of electronic devices under conditions that simulate the intended operating environment of the spacecraft as much as possible. We briefly discuss simulation of space radiation environments using various ground based radiation sources. As a specific example, we present the radiation evaluation of two optoelectronic devices to be used on the International Space Station under proton irradiation designed to simulate the low earth orbit environment.

Effects of High Energy Proton Irradiation on DC Performance of GaAs Metal-Semiconductor Field Effect Transistors

GaAs metal-semiconductor field effect transistors were exposed to 40 MeV protons at fluences up to 5 × 10 9 cm -2 . The extrinsic transconductance decreased from 98 to 68 mS mm -1 over this fluence range, with the drain-source current decreasing by ∼30% under the same conditions. Based on the increases observed in the reverse breakdown voltage and the channel resistance, the main degradation mechanism appears to be introduction of deep electron traps which reduce the effective doping in the channel. The device threshold voltage and diode ideality factor showed little change upon irradiation.