High linearity nanowire channel GaN HEMTs

Abstract

The performance of GaN-based high electron mobility transistors (HEMTs) has significantly improved over last decade through aggressive device scaling and the reduction of parasitic and short channel effects. However, in spite of the significant improvement in the DC/RF characteristics of short-channel devices, their performance is still below theoretical expectation and there have been several unexplained issues in the large-signal RF operation of these devices. One of these issues is the strong non-linear behavior of short-channel GaN HEMTs. The extrinsic transconductance (gm) of these devices quickly drops after reaching its peak value. There have been several theories to explain this behavior, including a non-linearity in the access resistance [1-3], optical phonon scattering [4], interface scattering [5], self-heating [6], and optical phonon bottleneck [7]. A second unexplained issue is that the maximum drain current in these devices is much lower than theoretical predictions. Recently, Shinohara et al. have demonstrated that self-aligned GaN devices with highly n+ doped regrowth contacts can solve both issues [8], but this approach limits the high voltage operation due to its low breakdown voltage. In this study, we have demonstrated sub-100 nm gate length GaN HEMTs with nanowire channel structure which can provide both high linearity and large breakdown voltage.