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.
This content will become publicly available on December 5, 2023
Strain localization in microelectronic devices commonly arises from device geometry, materials, and fabrication processing. In this study, we controllably relieve the local strain field of AlGaN/GaN HEMTs by milling micro-trenches underneath the channel and compare the device performance as a function of the relieved strain as well as radiation dosage. Micro-Raman results suggest that the trenches locally relax the strain in device layers, decreasing the 2DEG density and mobility. Intriguingly, such strain relaxation is shown to minimize the radiation damage, measured after 10 Mrads of60Co-gamma exposure. For example, a 6-trench device showed only ∼8% and ∼6% decrease in saturation drain current and maximum transconductance, respectively, compared to corresponding values of ∼15% and ∼30% in a no-trench device. Negative and positive threshold voltage shifts are observed in 6-trench and no-trench devices, respectively, after gamma radiation. We hypothesize that the extent of gamma radiation damage depends on the strain level in the devices. Thus, even though milling a trench decreases 2DEG mobility, such decrease under gamma radiation is far less in a 6-trench device (∼1.5%) compared to a no-trench device (∼20%) with higher built-in strain.
- Publication Date:
- NSF-PAR ID:
- 10408324
- Journal Name:
- Applied Physics Letters
- Volume:
- 121
- Issue:
- 23
- Page Range or eLocation-ID:
- Article No. 233502
- ISSN:
- 0003-6951
- Publisher:
- American Institute of Physics
- Sponsoring Org:
- National Science Foundation
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