Investigation of the interface between LPCVD-SiNx gate dielectric and III-nitride for AlGaN/GaN MIS-HEMTs

The interface between silicon nitride (SiNx) gate dielectric grown by low pressure chemical vapor deposition (LPCVD) and III-nitride heterostructure is investigated by a systematical comparison of AlGaN/GaN high-electron-mobility transistors (HEMTs) and metal-insulator-semiconductor HEMTs (MIS-HEMTs). A 20-nm LPCVD-SiNx grown at 650 °C features a high breakdown E-field of 13 MV/cm and a large conduction-band offset of 2.75 eV to GaN. High ON/OFF current ratio (∼1010) as well as breakdown voltage (∼878 V) is realized by employing the LPCVD-SiNx layer as both the gate and passivation dielectrics. Most important of all, about 2.6 × 1013 cm−2 positive fixed charges are confirmed to be present at the LPCVD-SiNx/III-nitride interface, as revealed by pulsed transfer characterizations and energy-band simulations. The trap density at LPCVD-SiNx/III-nitride interface is also experimentally determined.