The Study of Normally-on Power GaN HEMTs in QST Substrate with High Breakdown Voltage

This research investigated the normally-on GaN HEMTs with a particular emphasis on their impact on breakdown voltage. Through extensive experimentation involving GaN-on-QST and GaN-on-silicon (Si), and substrates, we highlighted the advantages of QST, particularly its poly-AlN composition, which enhances compatibility with the coefficient of thermal expansion (CTE). QST facilitates the growth of thicker buffer layers on larger substrates while preserving mechanical strength [1], contributing significantly to achieving a favorable breakdown voltage. We measured direct current (DC) performance on GaN-on-two different substrate HEMTs. These two samples maintained adequate electrical characteristics, including gate leakage, drain current, on/off ratio, and on-resistance. Notably, the breakdown voltage of GaN-on-QST sample exhibited the most outstanding performance which achieved 1500 V. These results emphasized the critical role of substrate material selection in optimizing GaN HEMT performance.