In this presentation, we will review the development status of III-N bipolar transistor switches and vertical GaN rectifiers. Early development of heterojunction bipolar transistors (HBTs) using AlGaN/GaN heterojunctions was unsuccessful because of the limited current drive and current gain. The GaN/InGaN HBTs, on the other hand, showed promising device performance. We studied optimized epitaxial growth in a metalorganic chemical vapor deposition (MOCVD) reactor, developed a direct-growth (or non-regrowth) mesa-type III-N HBT fabrication processing technology, and achieved state-of-the-art of GaN/InGaN NPN HBT performance.,,, These devices exhibited high-current gain of >100, high current drive density of >100 kA/cm2, and high d.c. power handling capability of > 3 MW/cm2. Small-signal microwave amplification with a cut-off frequency (fT) of 8GHz was also demonstrated experimentally. Similarly, GaN-based rectifiers have been studied in recent years and these devices have reportedly demonstrated switching performance approaching theoretical values. At Georgia Tech, our preliminary study demonstrated that 800-V homojunction GaN PIN rectifiers can achieve a specific on-state resistance of RON = 2.8 mOhm-cm2. The large turn-on voltage of GaN PIN diodes, however, could be problematic in circuit applications. To address this problem, GaN junction-barrier Schottky (JBS) rectifiers are also under study. Using a nickel as the Schottky contact material and an additional MOCVD regrowth step, our preliminary results demonstrated a GaN JBS diode with a turn-on voltage of ~0.8V, a value similar to typical silicon PN diodes. These results demonstrated the feasibility of using bipolar carrier transport mechanisms and PN junctions in III-N devices for power amplifications and switching circuits. Further device design and processing techniques that help achieve these performance characteristics will be discussed in the conference.
 Z. Lochner, et. al. , Appl. Phys. Lett. 99 (19), 193501-1–3 (2011).
 Y. Zhang, et. al. Phys. Stat. Sol. (c) 8 (7–8), 2451–2453 (2011).
 S. Shen et. al., IEEE Electron Device Lett., 32 (8), 1065–1067 (2011).
 Y. Lee, et. al. , Physica Status Solidi(a), 209(3), 497-500 (2012).
 T. Kao, et. al., IEEE Trans. Electron Devices, 62(8) 2679-2683 (2015).