K. K. Allums

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...

Influence of 60Co γ-rays on dc performance of AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) with different gate length and widths were irradiated with 60Co γ-rays to doses up to 600 Mrad. Little measurable change in dc performance of the devices was observed for doses lower than 300 Mrad. At the maximum dose employed, the forward gate current was significantly decreased, with an accompanying increase in reverse breakdown voltage. This is consistent with a decrease in effective carrier density in the channel as a result of the introduction of deep electron trapping states. The threshold voltage shifted to more negative voltages as a result of the irradiation, while the magnitude of the drain–source current was relatively unaffected. This is consistent with a strong increase of trap density in the material. The magnitude of the decrease in transconductance of the AlGaN/GaN HEMTs is roughly comparable to the decrease in dc current gain observed in InGaP/GaAs heterojunction bipolar transistors irradiated under similar conditions.

Electrical characteristics of proton-irradiated Sc2O3 passivated AlGaN/GaN high electron mobility transistors

Sc2O3-passivated AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated with 40 MeV protons to a fluence corresponding to approximately 10 years in low-earth orbit (5×109 cm−2). Devices with an AlGaN cap layer showed less degradation in dc characteristics than comparable GaN-cap devices, consistent with differences in average band energy. The changes in device performance could be attributed completely to bulk trapping effects, demonstrating that the effectiveness of the Sc2O3 layers in passivating surface states in the drain-source region was undiminished by the proton irradiation. Sc2O3-passivated AlGaN/HEMTs appear to be attractive candidates for space and terrestrial applications where resistance to high fluxes of ionizing radiation is a criteria.

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.

Magnesium oxide gate dielectrics grown on GaN using an electron cyclotron resonance plasma

Magnesium oxide was grown by gas source molecular beam epitaxy on (0001) oriented metalorganic chemical vapor deposition n-GaN using elemental Mg and atomic oxygen supplied from an electron cyclotron resonance plasma source. X-ray diffraction (XRD) indicated that the oxide was single crystal for TSUB=350 °C and mostly polycrystalline for TSUB=100 °C. Reflection high energy electron diffraction suggests that the films deposited at the lower temperature begin with a single crystal nucleation layer then quickly become polycrystalline. For both growth temperatures, the magnesium oxide was highly textured toward the (111) direction, with the polycrystalline samples showing a broader XRD peak but smoother surfaces. Single crystal MgO grown at 350 °C had high current leakage, prohibiting electrical measurements. A breakdown field of 2.3 MV/cm and an interface state density of 4×1011 cm−2 eV−1 were measured for the polycrystalline (TSUB=100 °C) magnesium oxide/GaN heterostructure.

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.

High-energy proton irradiation of MgO/GaN metal oxide semiconductor diodes

MgO/GaN metal oxide semiconductor diodes were irradiated with 40 MeV protons at a fluence of 5 X 10 9 cm - 2 , simulating long-term (10 yr) exposure in space-born applications. The result of the proton irradiation was a decrease in device capacitance, consistent with the creation of deep electron traps that reduce the effective channel doping and also a decrease in breakdown field from ∼10 6 V cm - 1 in control devices to 0.76 X 10 6 V cm - 1 in devices irradiated with the gate metal in place. The capacitance of the device irradiated with the contacts in place recovers to the same value as the contact diodes. The D i t values are decreased by the H 2 anneal in both the unirradiated and irradiated devices.

Effects of proton irradiation on the magnetic properties of GaGdN and GaCrN

GaGdN and GaCrN films grown by gas source molecular beam epitaxy were irradiated with high energy (10 and 40?MeV) protons at a fluence of 5 ? 109?cm?2 to examine the effect on magnetization. This dose is equivalent to the exposure expected in 10 years in low-earth orbit space missions. Both photoluminescence intensity and magnetization of the films showed significant decreases with irradiation. The largest response was observed with GaGdN, which experienced a 50?60% loss in band edge luminescence and 11?83% loss in magnetic saturation. After annealing the irradiated samples at 500?? C under a nitrogen plasma ambient, both types of films experienced a complete recovery in magnetic properties. The fact that the introduction of point defects did not increase the magnetization is evidence against unpaired bonds from defects in the film being responsible for the magnetic properties in the films.