GaN-based heterostructure field effect transistors and MMICs for high frequency applications

Gallium Nitride (GaN) based Heterostructure Field-Effect Transistors (HFETs) are a very promising candidate for high power and high frequency applications due to the high current and high breakdown voltage properties of GaN semiconductors and their related heterostructures. Two specific FET types, namely AlGaN/GaN High Electron Mobility Transistors (HEMTs) and AlN/GaN Metal Insulator Semiconductor FETs (MISFETs) were studied in this thesis. The work performed includes physical simulation, fabrication, characterization and small and large signal modeling of devices, as well as, their application to AlGaN/GaN HEMT Monolithic Microwave Integrated Circuit (MMIC) low noise amplifiers. Theoretical investigations and device simulations showed the potential of AlN/GaN heterostructure devices. These include higher carrier concentration, better control of the two Dimensional Electron Gas (2DEG) channel and smaller gate leakage than conventional AlGaN/GaN HEMTs. On the contrary, AlN/GaN MISFETs require a highly controlled growth technique and complex process approaches in order to ensure high quality ohmic contact formation. Approaches to overcome these difficulties are presented and the characteristics of successfully fabricated AlN/GaN MISFETs are reported using a KOH-based wet-etching technique for AlN. The large signal characteristics of AlN/GaN MISFETs were evaluated for the first time and showed promising power characteristics at microwave frequencies. For AlGaN/GaN HEMTs, various epitaxial layer designs were studied and device performance was optimized. AlGaN/GaN HEMTs and AlN/GaN MISFETs were modeled based on measured small and large signal characteristics and extracted physical parameters. The developed models showed good agreement with the device characteristics. A wideband balanced low noise amplifier with AlGaN/GaN HEMTs was designed and results are reported on its design methodology, circuit simulation, fabrication and experimental characteristics.