Download or read book Gallium Nitride Vertical Devices for High-power and High-frequency Applications written by Siwei Li and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gallium nitride (GaN) has gained considerable interest in the areas of power electronics and radio frequency (RF) devices in recent years due to its significantly higher material figure-of-merits (FOMs) than silicon (Si). The capability of operating faster as power switches also overwhelms another wide-bandgap contender, silicon carbide (SiC), especially for applications at ~600-1200 V level. GaN devices with a lateral topology such as high electron mobility transistors (HEMTs) have been extensively studied, while the development of vertical devices on high-quality free-standing GaN substrates is opening new opportunities towards improved power handling capability in high-power applications. There are still science and technology issues associated with GaN that limit its applications in high-power scenarios. One of the fundamental properties is its avalanche behavior, which is expected to be considered as a benchmark for the material but was rarely seen in GaN devices grown on foreign substrates, including sapphire, Si and SiC. Avalanche is observed and gaining increasing attention recently with the improvement of GaN-on-GaN substrate, especially in diodes. Several issues of GaN in high-power and high-speed applications are addressed in the present work. Edge terminations play a vital role in GaN devices targeting a high voltage range, and enable avalanche by optimizing the electric filed distribution, eliminating peak electric field at device edges. An ion-compensated moat etch structure is studied on GaN vertical p-n diodes. Parameters including moat etching depth and ion implantation dose are optimized. P-n diodes with a breakdown voltage (V[subscript BR]) of 1500 V and a specific on-state resistance (R[subscript ON,sp]) of 0.7 m[omega]·cm2 is demonstrated with the optimized structure, showing a device FOM of 3.2 GW·cm−2 and avalanche behavior. With avalanche performance as a prerequisite confirmed on vertical p-n diodes on bulk GaN substrates with dislocation density ranging from 1e4 cm−2 to 1e6 cm−2, the effect of dislocation density on device behavior, especially off-state leakage current is experimentally and studied in detail. The leakage mechanism is analyzed by considering its relationship to electric field and temperature. Lower leakage could be achieved on the substrate with 1e4 cm−2 dislocation density, with variable-range-hopping (VRH) procedure dominating low electric field range and Poole-Frenkel (PF) effect dominating the higher part, while VRH and other more trap-related processes may play more roles on the substrate with 1e6 cm−2 dislocation density. Large current capability is another factor for high-power applications. A DC current up to 50 A is successfully demonstrated on large-area p-n diodes by applying backside gold-to-gold thermal compression bonding. A successful scaling-up is achieved with essential factors studied. There have been few works on the RF performance of GaN vertical devices though the lateral RF devices have been widely explored. To study RF properties of GaN vertical devices, a Silvaco TCAD simulation model is established for nitride (N)-polar GaN current aperture vertical electron transistor (CAVET) based on a fitting of N-polar lateral HEMT experimental results. DC and RF properties of an N-polar CAVET are simulated, and a maximum output power of 15 W·mm−1 is expected. To experimentally demonstrate RF characteristics of a CAVET, the 1st-generation RF CAVET is then built on gallium (Ga)-polar substrate. Based on the DC characteristics, a current gain cutoff frequency (fT) at ~13 GHz is expected.