This work initially compares GaN high electron mobility transistors (HEMTs) based on the established Ga-face technology and the emerging N-face technology. An investigation is then carried out on the short channel effects in ultra-scaled GaN and InP HEMTs. The dielectric effects of the passivation layer in millimeter-wave, high-power GaN HEMTs are also investigated by focusing on the effective gate length, the gate fringing capacitance, and the drain-to-gate feedback capacitance. Lastly, efficient Full Band Monte Carlo particle-based device simulations of the large-signal performance of millimeter-wave transistor power amplifiers with high-Q matching networks are reported for the first time. In particular, a Cellular Monte Carlo code is self-consistently coupled with a Harmonic Balance frequency domain circuit solver. This book provides device engineers with an insight about the link between the nano-scale carrier dynamics and the device performance. It also introduces an efficient tool for the device early-stage design for RF power amplifiers.

This work has arisen out of the strong demand for a superior power-added efficiency (PAE) of AlGaN/GaN high electron mobility transistor (HEMT) high-power amplifiers (HPAs) that are part of any advanced wireless multifunctional RF-system with limited prime energy. Different concepts and approaches on device and design level for PAE improvements are analyzed, e.g. structural and layout changes of the GaN transistor and advanced circuit design techniques for PAE improvements of GaN HEMT HPAs.

This thesis presents the theory, design, and implementation of two high power (>10 W) RF power amplifiers operating in the S-band (2 to 4 GHz) and employing the Class F mode of efficiency enhancement. The amplifiers are based around gallium nitride (GaN) high electron mobility transistors (HEMTs) which provide the high power capability. A complex wideband design using synthesized low-pass transforming filters as large-bandwidth matching networks is presented, followed by a more elegant narrowband design employing simple stub matching networks for impedance matching and harmonic control. Also presented in this thesis is a detailed study into the computer modeling of the GaN HEMT devices in order to accurately predict their behavior when integrated into a system. A complete small-signal circuit model is developed which is capable of predicting the scattering parameters of the devices with a high degree of accuracy to the measured behavior. Large-signal device models of increasing complexity are studied to investigate fundamental behaviors of field-effect transistors for which HEMTs are a subset. Finally, the manufacturer design kit’s computer model is investigated and verified for accuracy with the measured results.An overview of power amplifier design and classes of operation is given, and specifically Class F theory and implementation are analyzed. The efficiency enhancement by waveform shaping is studied, as well as the mechanism of waveform shaping via harmonic manipulation. Once fabricated and tested, the wideband design is shown to achieve at least 38.8 dBm output power between 2.2 to 3.3 GHz centered around 2.75 GHz, giving a fractional bandwidth of 40%. Over that range, the PA is able to sustain PAE > 40%, with a peak efficiency of 61%. The narrowband design achieves an output power at its center frequency of 3 GHz of 41.48 dBm, or ~14 W, with the PAE achieving a maximum of approximately 66%.