Wide band-gap III-nitride semiconductors have great potential for the next generation of power electronics. GaN high-electron-mobility transistors (HEMTs) in particular have attracted great interest due to their high breakdown electric field and high electron mobility. With lower conduction loss and higher switching frequency, GaN-based transistors can improve the efficiency and reduce the size of many power electronics systems.

The standard AlGaN/GaN HEMTs are depletion-mode transistors. However, normally-off transistors are preferred in power electronics. Recently, our group has developed a new normally-off tri-gate GaN metal-insulator-semiconductor-field-effect-transistor (MISFET) ^[1] . By using a three-dimensional tri-gate structure and a sub-micron gate recess, we achieve high performance normally-off GaN transistors with a breakdown voltage as high as 565 V at a drain leakage current of 0.6 μA/mm. The new tri-gate normally-off GaN MISFET has a maximum current density of 530 mA/mm and an on/off current ratio of more than 8 orders of magnitude with a sub-threshold slope of 86±9 mV/decade, as Figure 1 shows. We have also demonstrated a new multi-finger technology with higher yield and lower device resistance for InAlN/GaN HEMTs. A multi-finger device with gate width of 39.6 mm has an on-resistance (R_on) of 0.244 Ω and a maximum current of 18.5 A, as in Figure 2(a).

Finally, ion-implantation isolation technology has also been developed. A state-of-the-art 1800 V breakdown voltage with 2.2 mΩcm² specific on-resistance has been achieved on AlGaN/GaN HEMTs on Si substrate (Figure 2(b)). Devices with ion-implantation isolation have higher breakdown voltage than devices using mesa-etching isolation, showing that ion-implantation isolation is a promising candidate for the next-generation high voltage GaN-based HEMT fabrication.

1. B. Lu, E. Matioli and T. Palacios, “Tri-gate normally-off GaN power MISFET,” IEEE Electron Device Letters, vol. 33, no. 3, pp. 360-362, 2012.