Thermo-mechanical aspects of gamma irradiation effects on GaN HEMTs

Abstract

We report thermal and mechanical responses accompanying electrical characteristics of depletion mode GaN high electron mobility transistors exposed to gamma radiation up to 107 rads. 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 106 rads. 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 107 rads 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.

Heavy ion irradiation induced failure of gallium nitride high electron mobility transistors: effects of in-situ biasing

“…The ON mode device shows further degradation (figure 6(a)) near the gate edge, where the highest electric field is generated when the gate voltage is applied. This implies that the highly stressed region is more vulnerable to incoming radiation [6]. The degradation observed in figures 6(b) and (c) for the interface in the ON-mode device is also similar to that observed in the OFF-mode device.…”

“…After 0.01 dpa, V th shifted further positive to −2.6 V, but transconductance increased by 17% compared to 0.001 dpa. The increase in the transconductance can be attributed to the irradiation-induced strain relaxation AlGaN/GaN HEMTs, which occur at lower fluence [6,28,40]. During ion irradiation, both donor and acceptor trap creation had been reported [24,28,41].…”

“…A large electric field appears under the gate edge across the barrier in the AlGaN/GaN HEMTs, adding to the existing substantial intrinsic tensile strain at the interface due to lattice mismatch [5]. To make matters worse, ionizing and non-ionizing radiation may significantly impact the device's performance as well [2,6]. The most common trend is to study radiation effects on devices at the OFF state, ignoring the stressors originating from the operational conditions and the combined effect of irradiation.…”

Nanoscale Stress Localization Effects on the Radiation Susceptibility of GaN High‐Mobility Transistors

“…Such displacement damage resulted in a ≈16% decrease in saturation current in the device and a ≈6% decrease in transconductance. [ 17 ] Leakage current was most adversely affected, with an increase of ≈3 orders of magnitude. The details on the degradation of electrical characteristics are given in Figure .…”

“…Compressive stress increases the electron's effective mass and decreases atomic binding energy (more rapidly than a tensile stress), making the GaN layer vulnerable to compression. [ 17 ] The stress measurement technique, therefore, plays a critical role. For example, Raman spectroscopy captures the GaN layer stress as the laser penetrates the surface passivation and ultra‐thin AlGaN layer.…”