UC San Diego

Transistors are the backbone of any electronic system. The Si complementary metal-oxide-semiconductor (CMOS) technology with extremely scaled process has governed the electronic world in the last few decades, but many other materials with novel design architectures are emerging to alternate it in some applications. Gallium nitride (GaN) is one of them and coming into view recently for high power and high frequency applications due to the surge of electric power usage and data transmission rate.

This dissertation provides a comprehensive study of two types of GaN transistors, lateral and vertical, for power electronics and wireless communications. The first half of the dissertation investigates vertical GaN transistors for high power switches. The epitaxial layers grown by a novel selective area growth (SAG) method on a Si substrate were utilized to pursue demonstration of cheap and high-performance GaN devices, and commercialized GaN wafers were used to identify and resolve existing problems, and to improve the key device metrics. An evolution of the vertical GaN transistor by optimizing the device design and the fabrication process is shown and discussed in detail with experiments and TCAD simulations.

In the second half of this dissertation, we propose a novel approach to address the intrinsic linearity of GaN transistors for radio frequency (RF) amplifiers. A new device design methodology was presented by simple lithographic modifications that can create a flat transconductance (gm) profile for AlGaN/GaN Fin field-effect transistors (FinFETs). Then, it is discussed how this flat gm impacts on the intermodulation distortion characteristics at microwave as well as millimeter wave frequencies with a record linearity figure-of-merit at 5 GHz. Finally, with a measured noise performance of the realized device, we present a record dynamic range figure-of-merit at 30 GHz for GaN transistors and much higher linearity performance than any existing semiconductor technologies, exhibiting a great potential for mm-wave low noise amplifiers (LNAs).