N-polar GaN/AlGaN/AlN high electron mobility transistors on single-crystal bulk AlN substrates

Recent observation of high density polarization-induced two-dimensional electron gases in ultra-thin N-polar GaN layers grown on single-crystal AlN has enabled the development of N-polar high electron mobility transistors (HEMTs) on AlN. Such devices will take advantage of thermal and power handling capabilities of AlN, while simultaneously benefitting from the merits of N-polar structures, such as a strong back barrier. We report the experimental demonstration of N-polar GaN/AlGaN/AlN HEMTs on single-crystal AlN substrates, showing an on-current of 2.6 A/mm with a peak transconductance of 0.31 S/mm. Small-signal RF measurements revealed speeds exceeding f(t)/f(max) = 68/100 GHz. These results pave the way for developing RF electronics with excellent thermal management based on N-polar single-crystal AlN.