Top-down AlN/GaN enhancement- & depletion-mode nanoribbon HEMTs

III-V nitride HEMTs are currently being intensively investigated for both depletion and enhancement mode operation at high powers and high frequencies. Among the various methods that can render the polarization-doped HEMTs enhancement-mode, the least investigated are those that exploit 3-D nanoscale geometrical electrostatic effects. Recently, bottom-up grown GaN nanowire MISFETs have shown respectable depletion-mode device performance. However, the handling of isolated nanowires is technologically challenging. This paper demonstrates that by combining conventional epitaxially grown AIN/GaN HEMT structures with top-down nanoribbon fabrication, both E-mode and D-mode HEMTs with high performance can be realized in a facile manner, and allow integration on the same substrates. In addition to the ease of realizing E-mode and D-mode devices, these top-down nanoribbon HEMTs also take advantage of the superior electrostatics of wrap-gates and quasi-1D charge transport for high performance.