UC Santa Barbara

There is a strong need for a large band gap pFET device with good performance for an efficient high voltage CMOS platform for power conversion applications. GaN is a leading choice of material for high power applications. GaN HEMTs are already commercially used in high power conversion systems. However, the performance of the GaN pFETs have not been attractive enough for a GaN based CMOS power conversion technology.Work in this dissertation focuses on improving the on-current of hole channel GaN transistors while maintaining normally off operation. Lower hole mobility requires a much higher hole channel charge to achieve an on-resistance of the same order as GaN HEMTs. One approach is to distribute the total carriers in multiple parallel channels and modulate these parallel channels independently. A Mg-doped GaN/AlGaN superlattice (SL) is one way to get multiple parallel hole channels. The effects of different superlattice parameters were studied using self-consistent Poisson-Schrodinger solver. Using MOCVD grown GaN/AlGaN superlattice, FinFET devices were designed, fabricated, and characterized. The first generation of devices employing MIS gate structure showed normally-on operation with >100 mA/mm. Next, Schottky gate structures were used to achieve normally-off operation. These devices used a dry etch induced sidewall tunnel junction contacts, which led to turn-on voltage in the device output characteristics. MOCVD regrown p+ GaN contact layer process was developed to remove this turn-on voltage. Both blanket and selective area regrown contact process were optimized. Finally, the regrown contact process was integrated with the FinFET process. MOCVD regrown contacts around the fins led to FinFET devices with normally-off operation, >60 mA/mm on-current and 42 V breakdown voltage.