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We report thermal and mechanical responses accompanying electrical characteristics of depletion mode GaN high electron mobility transistors exposed to gamma radiation up to 107rads. Changes in the lattice strain and temperature were simultaneously characterized by changes in the phonon frequency of E2(high) and A1(LO) from the on-state and unpowered/pinched off reference states. Lower doses of radiation improved electrical properties; however, degradation initiated at about 106rads. We observed about 16% decrease in the saturation current and 6% decrease in the transconductance at the highest dose. However, a leakage current increase by three orders of magnitude was the most notable radiation effect. We observed temperature increase by 40% and mechanical stress increase by a factor of three at a dose of 107rads compared to the pristine devices. Spatial mapping of mechanical stress along the channel identifies the gate region as a mechanically affected area, whereas the thermal degradation was mostly uniform. Transmission electron microscopy showed contrast changes reflecting a high vacancy concentration in the gate region. These findings suggest that localized stress (mechanical hotspots) may increase vulnerability to radiation damage by accommodating higher concentration of defects that promote the leakage current.
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Non-Thermal Annealing of Gamma Irradiated GaN HEMTs with Electron Wind Force
Radiation damage mitigation in electronics remains a challenge because the only established technique, thermal annealing, does not guarantee a favorable outcome. In this study, a non-thermal annealing technique is presented, where electron momentum from very short duration and high current density pulses is used to target and mobilize the defects. The technique is demonstrated on 60 Co gamma irradiated (5 × 10 6 rad dose and 180 × 10 3 rad h −1 dose rate) GaN high electron mobility transistors. The saturation current and maximum transconductance were fully and the threshold voltage was partially recovered at 30 °C or less. In comparison, thermal annealing at 300 °C mostly worsened the post-irradiation characteristics. Raman spectroscopy showed an increase in defects that reduce the 2-dimensional electron gas (2DEG) concentration and increase the carrier scattering. Since the electron momentum force is not applicable to the polymeric surface passivation, the proposed technique could not recover the gate leakage current, but performed better than thermal annealing. The findings of this study may benefit the mitigation of some forms of radiation damage in electronics that are difficult to achieve with thermal annealing.
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- Award ID(s):
- 2015795
- PAR ID:
- 10399316
- Date Published:
- Journal Name:
- ECS Journal of Solid State Science and Technology
- Volume:
- 11
- Issue:
- 7
- ISSN:
- 2162-8769
- Page Range / eLocation ID:
- 075002
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1149/2162-8777/ac7f5a
