I. Introduction
Gallium nitride (GaN) devices experience an explosive and rapid development with new device providers and new devices entering the market at an impressive speed. However, the devices are HEMT (High Electron Mobility Transistor) type lateral devices utilizing the two-dimensional electron gas (2DEG) properties of the GaN/AlGaN interface. The required GaN layers in the devices are grown epitaxially on hetero substrates like Si, SiC, sapphire and poly-AlN using buffer layers to control the strain caused by lattice mismatch which prevents the vertical current flow. For power applications the lateral current flow close to the surface leads to thermal limitations and complicates thermal management in packaging. Furthermore, it leads to large footprint of the devices for large currents. The devices also lack the robust avalanche breakdown characteristics. At present the HEMT power devices are limited to operational voltages of less than 650 V with some first devices from VisIC and iGaNPower demonstrating 1200 V capability. For these reasons there is an interest in the development of vertical GaN devices opening the possibilities of small footprint and thus lower cost due to smaller chip sizes, high power densities and robust avalanche breakdown characteristics with large avalanche energy capability [1]. The development of vertical devices has been hindered by the lack of large area freestanding GaN substrates facilitating homoepitaxial growth of drift layers. An alternative are semi-vertical structures grown on Si which are the subject of this study along with true vertical structures on GaN. In addition to the material issues there are technological issues that require further attention like dopant compensation and activation and Mg implantation technology for junction termination. This paper focuses on prospective benchmarking of semi-vertical and vertical GaN MOSFETs against SiC devices. A beyond the state-of-the-art benchmarking, in wide voltage range, is missing in the literature. Most of the benchmarking publications report results of experimental structures based on state-of-the-art technology and simple junction termination [2]–[4].