Spyros Pavlidis - Next-Generation Vertical GaN Power Devices Using Selective-Area Doping Techniques
From Katie Gentilello
In recent years, there has been a surge of research and commercial interest in gallium nitride (GaN)-based devices for power conversion applications. This is largely motivated by the wide bandgap of GaN, which offers a unipolar limit of performance that is larger than that of silicon and silicon carbide. While lateral transistors have already been commercially adopted, high power applications require vertical devices to control chip size. Recent improvements in native GaN substrate quality and epitaxy have unlocked the potential of vertical GaN power devices, but effective strategies for selective area doping, in particular p-type doping, remain a major challenge.
In this talk, two vertical devices that rely on selective area doping will be discussed. Firstly, the use of magnesium (Mg) implantation and ultra-high pressure annealing (UHPA) will be explored for the development of GaN junction barrier Schottky (JBS) diodes. Effective crystal repair and carrier activation post implantation via UHPA, which is a capless technique, will be demonstrated. The impact of UHPA on the formation of rectifying contacts will then be investigated, followed by the key demonstration of a 900 V GaN JBS diode with state-of-the-art specific on resistance (RON,sp). The second device that will be studied is the GaN superjunction (SJ) diode. Here, lateral polar junctions (LPJs) are adopted. This approach exploits the natural doping asymmetry between the N-polar and Ga-polar crystal orientations to simultaneously grow N-polar GaN for the n-type pillars and Ga-polar GaN for the p-type pillars, which represents a uniquely different strategy compared to conventional semiconductor technologies. It will be shown that the N-polar GaN camel diode can be used to tune the barrier height and reduce leakage. In this way, the first charge-balanced GaN superjunction device will be demonstrated. All in all, these innovations represent key experimental building blocks for future high-power GaN power devices.