Kei May Lau is a Research Professor at the Hong Kong University of Science & Technology (HKUST). She received her degrees from the University of Minnesota and Rice University and served as a faculty member at the University of Massachusetts/Amherst before joining HKUST in 2000. Lau is a member of the US National Academy of Engineering, a Fellow of IEEE, Optica (formerly OSA), and the Hong Kong Academy of Engineering. She was also a recipient of the IPRM award, IET J J Thomson medal for Electronics, Optica Nick Holonyak Jr. Award, IEEE Photonics Society Aron Kressel Award, US National Science Foundation (NSF) Faculty Awards for Women (FAW) Scientists and Engineers, and Hong Kong Croucher Senior Research Fellowship. She was an Editor of the IEEE Transactions on Electron Devices and Electron Device Letters, an Associate Editor for the Journal of Crystal Growth and Applied Physics Letters.
Lau’s research focuses on the development of monolithic integration of semiconductor devices and systems on industry-standard silicon substrates by MOCVD. Her patented LED-on-Silicon (LEDoS) monolithic micro-LED arrays driven by a CMOS backplane have been commercialized for smart glass applications with full-color micro-displays. Her group has also been investigating the growth of GaN vertical trench MOSs on foreign and native substrates for high-performance power devices.
Vertical GaN-based power devices have tremendous potential in achieving high power handling capabilities and power delivery density compared with lateral GaN HEMTs [1]. Two terminal PIN diodes and trench MOSFETs stand out as simple choices that can offer switching and intrinsic normally-off operation with a p-GaN inversion channel, providing a high positive threshold voltage to prevent false turn-on. The p-n junction for OFF-state blocking can provide avalanche capability, which is vital for high power applications. Furthermore, a relatively simple fabrication process requiring no regrowth has been demonstrated.
Quasi-vertical GaN trench MOSFETs can be grown on cost-effective foreign substrates, such as sapphire and silicon[2]. For fully-vertical devices with drain contact at the substrate backside, GaN-on-silicon trench MOSFETs have been materialized using a complicated substrate removal process.
Alternatively, trench MOSFETs on a conductive buffer grown on doped substrates would greatly simplify the fabrication process. SiC has been shown to be the most sensible choice to realize high-performance fully-vertical GaN-on-SiC diodes with a conductive AlGaN buffer. In addition to the advantage of smaller mismatch between GaN and SiC, the high thermal conductivity of SiC substrates is highly desirable for power applications. It’s also possible to integrate GaN and SiC devices to combine their advantages if a GaN-on-SiC platform is used [3]. Recently, quasi-vertical GaN-on-SiC FinFETs are demonstrated. The challenge of growing trench VMOS on SiC is optimization of the conductive buffer to grow a thick drift layer. The other option is using highly doped native GaN substrates.
We will discuss the growth of GaN-based diodes and trench MOS on all the different substrates to balance all the trade-offs of the on- and off-state characteristics of the devices. For the OFF-state, electric field crowding at trench corners can lead to premature breakdown. We also developed a trench etching process and application of a thick bottom dielectric (TBD) in fully-vertical GaN-on-GaN trench MOSFETs, which mitigates this electric field crowding and successfully increases the breakdown voltage (VBR)T.
REFERENCES
[1] Andrew T. Binder et al., Appl. Phys. Express, 17, 101003, 2024.
[2] R. Zhu et al., IEEE Electron Device Lett., 43, 346-349, 2022.
[3] J. Li et al., IEEE Electron Device Lett., 46, 282-285, 2025.