High-voltage GaN-on-Si hetero-junction FETs with reduced leakage and current collapse effects using SiNx surface passivation layer deposited by low pressure CVD

Abstract

We have investigated the effects of surface passivation on off-state leakage current and current collapse effects of high-voltage GaN-on-Si hetero-junction field effect transistors (HFETs) by using low pressure chemical vapor deposition (LPCVD) of silicon nitride (SiNx). In this work, the metal–oxide–semiconductor (MOS) structure-based HFETs are realized on AlGaN/GaN epitaxy grown silicon substrates by metal–organic chemical vapor deposition (MOCVD). For a comparative study, we have fabricated two types of HFETs, standard and modified MOS-HFETs. In the modified MOS-HFETs process, the surface passivation layer of SiNx is deposited by LPCVD after the mesa isolation step, while the gate is deposited and self-aligned in the trench etched in LPCVD-SiNx layer using inductively coupled plasma reactive ion etching (ICP-RIE). The high temperature deposition of LPCVD-SiNx prevents the degradation caused by the ohmic annealing and other process-induced surface damage. Compared to the standard MOS structure, the modified MOS-HFET devices exhibit 10 times lower off-state leakage currents within high voltage range (0–800 V) and significantly alleviated current collapse effects simultaneously.