Wide band-gap III-nitride semiconductors have excellent potential for next-generation power electronics systems.\u00a0 AlGaN\/GaN high-electron-mobility transistors (HEMTs) have attracted great interest due to their high breakdown electric field and high electron mobility.\u00a0 InAlN\/GaN HEMTs also show great promise for high-performance power electronic switches, due to the very high sheet charge density induced by the polarization difference between InAlN and GaN. Transistors built from GaN could theoretically have 3 orders of magnitude reduction in on-resistance compared to Si power devices.\u00a0 With lower conduction loss and higher switching frequency, they can improve the efficiency and reduce the size of many power electronics systems.<\/p>\n
Wide-periphery AlGaN\/GaN transistors with Wg<\/sub>=80 mm have been designed and successfully fabricated, as Figure 1 shows.\u00a0 These devices were flip-chip solder-bumped and placed in a power converter circuit (designed by Professor Perreault\u2019s group) resulting in 92.72% efficiency at 25 W.\u00a0 To ensure that the device did not suffer from breakdown or dramatic dynamic on-resistance during the converter operation, passivation and field-plate structures were optimized.\u00a0 Work is ongoing to integrate the enhancement mode tri-gate technology[1<\/a>]<\/sup> with these wide-periphery devices.<\/p>\n InAlN\/GaN devices with an off-state breakdown voltage of 3000V and a low specific on-resistance of 4.25 m\u03a9\u2219cm2<\/sup> were also fabricated[2<\/a>]<\/sup>.\u00a0 In order to suppress sub-threshold current leakage, an AlGaN back-barrier was used to better confine the channel electrons in these devices, as shown in Figure 2.<\/p>\n Finally, the thermal characteristics of lateral AlGaN\/GaN HEMTs and vertical MOSFET power transistors were analyzed using a self-consistent electro-thermal simulation.\u00a0 It was found that although the lateral device structure offers better performance for breakdown voltage below 200 V, the vertical transistors have the potential (although at a substantially higher cost) for higher power density at or above 600 V[3<\/a>]<\/sup>.<\/p>\n\n\t\t