Principal Investigator Carl Thompson
High electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures have been studied in literature for a variety of high-frequency and high-power applications. To minimize lattice mismatch and suppress defects generation, HEMTs, under study, are mostly fabricated on sapphire or SiC substrates. Currently, there is strong interest to fabricate GaN HEMTs on silicon substrates due to its low cost and compatibility with complementary metal–oxide–semiconductor (CMOS) integration technology. However, market adoption of this technology is still limited by the HEMT device reliability.
We have investigated the effects of SixN1-x passivation density on the reliability of AlGaN/GaN- on-Si HEMTs. Upon stressing, devices degrade in two stages: fast-mode degradation, followed by slow-mode degradation. Both degradations can be explained by different stages of pit formation at the gate edge. Fast-mode degradation is caused by pre-existing oxygen at SixN1-x /AlGaN interface. It is not significantly affected by the SixN1-x density. On the other hand, slow-mode degradation is associated with SixN1-x degradation caused by electric-field-induced oxidation. By using high-density SixN1-x, the slow-mode degradation can be minimized.
Devices for research purposes are usually designed and fabricated in a way that certain failure can be magnified to study the failure mechanism better. However, commercial devices focus more on reliability and performance maximization. In ongoing research, we are also interested in characterizing the reliability of commercial GaN HEMTs produced by CREE Inc. A statistical reliability model will be developed, and comparison.