Gallium nitride-based HEMTs for microwave power and noise: Physics and application

AlGaN/GaN high electron mobility transistors (HEMTs) have shown promising high speed performance, both high microwave power and low microwave noise. In this dissertation, the millimeter-wave and microwave power performance and small signal and low noise microwave characteristics are investigated. The CW power performance at 20 GHz and 30 GHz of 0.25 mum x 100 mum AlGaN/GaN HEMTs grown by metal-organic chemical vapor deposition (MOCVD) on semi-insulating SiC substrates is reported. Saturated output power at 20 GHz was 6.4 W/mm with 16% power added efficiency (PAE), and output power at 1-dB compression at 30 GHz was 4.0 W/mm with 20% PAE. This is the highest power reported for 0.25-mum gate-length devices at 20 GHz, and the 30 GHz results are among the highest power millimeter-wave power data published to date on GaN-based devices. This work also investigates the dependence of power performance on bias and temperature. The small signal performance on bias and temperature of GaN-based HEMTs are investigated via a systematic model extraction routine, and for the first time a fully monolithic AlGaN/GaN HEMT-based low noise amplifier (LNA) is reported. The monolithic microwave integrated circuit (MMIC) demonstrated a noise figure of 3.5 dB, gain of 7.5 dB, input return loss of -7.5 dB, and output return loss of -15 dB at 8.5 GHz. The MMIC was fabricated on layers grown by MOCVD on a silicon carbide substrate and employed a 0.25-mum x 150-mum AlGaN/GaN HEMT. These results demonstrate the potential for the integration of a robust low noise amplifier with an ultra-high performance power amplifier in a single GaN-based technology for next-generation military and communication systems.