Ultra-thin Body GaN-on-insulator nFETs and pFETs: Towards III-nitride complementary logic

Ultra-thin body (UTB) devices with tight electrostatic and quantum confinement of charge carriers have been well developed in highly scaled silicon CMOS technology. For adopting such advanced methods, III-nitrides can benefit immensely from epitaxial AlN as the substrate platform, in contrast to conventional GaN-based substrate platform. With its large polarization charge, wide bandgap and large band offsets, AlN induces the maximal carrier densities while providing the best confinement for nitride channels of all compositions. Such devices stand also to benefit from the symmetry of electronic polarization: high density hole gases can be generated in much the same way as the high density 2DEG in GaN HEMTs, thus enabling p-channel FETs on the same material platform in a logical manner. The AlN/GaN heterojunctions where mobile carriers are located are epitaxial, and excellent transport properties are expected as opposed to the rougher oxide-semiconductor interfaces. Furthermore, AlN is an excellent electrical insulator but simultaneously an excellent thermal conductor, which makes it highly attractive to act as back-barrier and to lower junction temperatures in high power devices by efficient heat dissipation. There have been reports on relaxed GaN n-channel FETs (nFETs) on AlN [1, 2] and III-nitride based p-channel field effect transistors (pFETs) [3, 4]. All the prior work uses relaxed GaN as the channel, and strained GaN channels on AlN have not been explored before. In this work we demonstrate UTB GaN nFETs [5] and pFETs on AlN grown by molecular beam epitaxy (MBE) as the first step towards complementary logic and high power applications.