Electrical and structural characteristics of aged RF GaN HEMTs and irradiated high-power GaN HEMTs with protons and heavy ions

Leading GaN HEMT manufacturers have reported excellent RF power characteristics and encouraging reliability. However, long-term reliability in the space environment still remains a major concern due to a number of defects and traps as well as unknown degradation mechanisms. Thus, careful study of reliability and radiation effects of GaN HEMTs should be performed before GaN HEMT technology based solid state power amplifiers (SSPAs) are successfully deployed in space satellite systems. We studied both RF GaN HEMTs fabricated per our design and commercial high-power GaN HEMTs, both grown on SiC substrates. Our RF devices had a nominal Ni-Au Schottky gate length of 0.25 μm, a total gate width of 6 × 150 μm periphery, and a field plate, while high-power devices had a Ni-Au Schottky gate length of 0.4 μm, a total gate width of 10 × 350 μm periphery, and a field plate. First, DC and RF characteristics of RF devices were compared before and after they were aged under different conditions (DC and temperature). Focused-ion-beam was employed to prepare TEM cross sections from degraded devices for defect analysis using a high-resolution TEM. Also, we performed strain analysis on pristine and degraded devices using TEM-based techniques. Second, DC characteristics of high-power devices were compared before and after they were irradiated with protons and heavy ions. Some of devices were exposed while they were unbiased, DC biased, and DC and RF biased.