SiC and GaN from the viewpoint of vertical power devices

Abstract

Summary form only given. Wide-bandgap (WBG) semiconductors have attracted great attention as materials for the next-generation power devices since they have superior material properties compared to silicon (Si). The most advanced WBG semiconductor for power devices is silicon carbide (SiC). In 1987, the growth technology called “step-controlled epitaxy”, which enables single-phase (polytype) growth, was developed. In 1993-1994, SiC Schottky-barrier diodes (SBDs) which exceeds the Si material limit was demonstrated. In 2001, SiC SBDs were commercialized. Key technologies for SiC SBDs were edge termination to obtain an ideal breakdown voltage and a junction barrier Schottky (JBS) structure to suppress reverse leakage current. For power MOSFETs, it took longer time due to low channel mobility at SiO2/SiC and oxide reliability issues. Channel mobility was much improved by post-oxidation nitridation in NO or N2O ambient. Now, channel mobility and reliability are well controlled (balanced). SiC power MOSFETs as well as power modules with SiC MOSFETs and SiC SBDs, are commercially available. Last 5 years, the implementation of SiC devices into electronic vehicles and railway trains were extensively investigated, demonstrating a significant improvement of power efficiency. Gallium nitride (GaN) is another candidate for power devices. AlGaN/GaN HEMTs were originally developed for high-power high-frequency amplifiers, however in the last decade extensive development efforts were carried out on AlGaN/GaN HEMTs grown on Si substrates producing cost-effective high-efficiency power switching devices, which commercial companies have started into production. They have a great impact on consumer electronics due to their excellent performance of low on-resistance with high switching speed, which can never be realized by Si power devices. Recently, GaN vertical power devices have attracted great attention for power devices with large breakdown voltage and large current handling capability. Some of technologies of GaN HEMTs can be used for GaN vertical power devices. However, many new technologies should be developed to realize high-performance GaN vertical power devices. Here, we can learn many things from the history of SiC power devices. In this talk, the author would like to discuss challenges for GaN vertical power devices by referring SiC technologies. It is interesting that some of challenges are easy for SiC but very tough for GaN, and vice versa.