Cumulative Impacts of Proton Irradiation on the Self-heating of AlGaN/GaN HEMTs

The impact of proton irradiation on the self-heating of AlGaN/GaN high-electron-mobility transistors (HEMTs) was studied at an energy of 1 MeV and under a fluence level of 2 × 1015 cm-2. Severe degradation in electrical characteristics was observed under these conditions (5× reduction in drain saturation current at VGS = 0 V, positive shift in threshold voltage by 3.1 V). Concomitantly, an 80% increase in the device gate temperature was observed using a thermoreflectance thermal imaging technique, at a power dissipation level of 5 W/mm. One of the key contributing factors behind this exacerbated self-heating for the irradiated devices was found to be the increased electric field concentration at the drain side of the gate edge because of a higher drain-source voltage level required to operate the device at the same power density condition before irradiation. Additionally, reduction in thermal conductivity of the gallium nitride (GaN) layer and the silicon (Si) substrate led to increased thermal resistance and, hence, an increased device operating temperature. According to the stopping and range of ions in matter (SRIM) simulation, the penetration depth for the protons was ∼8.8 μm under the tested conditions. As the GaN/Si interface structure (including the AlGaN strain-relief layer) for the tested HEMTs was about 5 μm away from the surface, significant damage occurred near this heterointerface. This damage resulted in an ∼3× increase in the effective interfacial thermal boundary resistance that contributed to an additional 16% increase in device self-heating. Overall, the degradation of electrical parameters (24%), the GaN thermal conductivity (33%), the GaN/Si effective thermal boundary conductance (16%), and the Si substrate thermal conductivity (20%) contributed to the exacerbated self-heating in the irradiated AlGaN/GaN HEMT (∼90 °C) as compared to that of the reference (i.e., nonradiated) HEMT (∼50 °C), under a power density condition of 5 W/mm.