ABSTRACT
This chapter describes a few key process steps to fabricate GaN high-electron-mobility transistors (HEMTs) for power electronics applications. The whole process flow to fabricate a HEMT mainly includes five steps, namely mesa isolation, ohmic contact formation, gate formation, pad and interconnection metallization, and surface passivation. Sometimes, to reduce the gate leakage current, an additional step of gate dielectric deposition is included before the gate metal deposition in order to form a structure called metal-insulator-semiconductor HEMT (MIS-HEMT) or metal-oxide-semiconductor HEMT (MOS-HEMT). Usually a field plate is also required to improve the breakdown voltage and suppress the surface trapping effect. The wet-etching rates of GaN by chemicals highly depend on the quality of the material. Dry etching by plasma is widely used in the fabrication of various GaN devices, including PN diodes and Schottky barrier diodes (SBDs), HEMTs, light-emitting diodes (LEDs), and lasers.
