AlGaN/GaN/AlN ‘Buffer-Free’ High Voltage MISHEMTs with Si-rich and Stoichiometric SiNx First Passivation

‘Buffer-free’ AlGaN/GaN/AlN high electron mobility transistors (HEMTs) with a thin GaN channel layer and a thin AlN nucleation layer grown on a semi-insulating SiC substrate are presented. Si-rich and a stoichiometric low-pressure chemical vapor deposition (LPCVD) SiNx first passivation were employed to study the impact of stoichiometry on off-state leakage currents in GaN-based metal-insulator-semiconductor (MIS)HEMTs. Nitrogen implantation isolation, SiOx second passivation, gate and source field plates were utilized. Off-state drain leakage current was reduced 2–3 orders of magnitude by depositing a stoichiometric instead of a Si-rich SiNx passivation. The gate leakage current was suppressed below 10nA/mm until breakdown. A destructive breakdown voltage of 1742V and 1532V was measured for the MISHEMTs with Si-rich and stoichiometric SiNx passivation, respectively. This demonstrates how high voltage, low leakage MISHEMTs can be achieved using a ‘buffer-free’ heterostructure by optimizing the first passivation stoichiometry.