Investigation of Isolation Approaches and the Stoichiometry of SiNx Passivation Layers in "Buffer-Free" AlGaN/GaN Metal-Insulator-Semiconductor High-Electron-Mobility Transistors

Critical process modules for the fabrication of metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) based on a novel 'buffer-free' AlGaN/GaN heterostructure grown with metal-organic chemical vapor deposition (MOCVD) are presented. The methods of isolation and passivation for this type of heterostructure are investigated. Utilizing nitrogen implantation, it is possible to achieve off-state destructive breakdown voltages (BVs) of 2496 V for gate-drain distances up to 25 mu m, whereas mesa isolation techniques limit the BV below 1284 V. The stoichiometry of the SiNx passivation layer displays a small impact on the static and dynamic on-resistance. However, MISHEMTs with Si-rich passivation show off-state gate currents in the range of 1-100 mu A mm(-1) at voltages above 1000 V, which is reduced below 10 nA mm(-1) using a stoichiometric SiNx passivation layer. Destructive BVs of 1532 and 1742 V can be achieved using gate-integrated and source-connected field plates for MIHEMTs with stoichiometric and Si-rich passivation layers, respectively. By decreasing the field plate lengths, it is possible to achieve BVs of 2200 V. This demonstrates the implementation of MISHEMTs with high-voltage operation and low leakage currents on a novel "buffer-free" heterostructure by optimizing the SiNx stoichiometry.