The effects of an LPCVD SiN (x) stack on the threshold voltage and its stability in AlGaN/GaN MIS-HEMTs

In this work, we systematically studied the stoichiometry and thickness effects of low-pressure chemical vapor deposited SiN (x) bilayer stacks on the electrical properties of AlGaN/GaN heterojunction-based metal-insulator-semiconductor high electron mobility transistors. A Si-rich SiN (x) single layer reduces threshold voltage shift and hysteresis under gate stress but gives rise to high gate leakage. A near-stoichiometric SiN (x) single layer suppresses gate leakage but causes poor gate stability. A bilayer SiN (x) stack with an optimized thickness ratio improves both the gate stability and on-resistance while maintaining a low current leakage. The bilayer SiN (x) stack consisting of a 5 nm Si-rich SiN (x) interfacial layer and a 15 nm SiN (x) capping layer resulted in the lowest sheet resistance and the highest gate stability. Such enhanced gate stability is explained by the low density of trap states and the weakened electric field at the Si-rich SiN (x) /GaN interface and an extra positive charge at the bilayer interface.