Subcritical barrier AlN/GaN E/D‐mode HFETs and inverters

Enhancement‐ and depletion‐mode AlN/GaN HFETs have been fabricated with a subcritical barrier design: a two‐dimensional electron gas (2DEG) is induced in the highly resistive as‐grown heterostructure when a suitable capping material is deposited over the ultrathin AlN barrier. In this bottom‐up approach 2DEGs can be locally induced by patterned cap layers on subcritical barrier AlN/GaN heterostructures, which can enable the monolithic integration of enhancement‐ and depletion‐mode HFETs. An inverter circuit with 1.5 nm ultrathin AlN barrier E‐ and D‐mode HFETs was successfully demonstrated with reasonable voltage transfer characteristics, noise margin, and gain. To our best knowledge this is the first reported inverter based on subcritical barrier III–V nitride heterostructures. magnified image Integration of E‐ and D‐mode HFETs in a subcritical barrier AlN/GaN heterostructure, where n2DEG ∼ 0 in the as‐grown structure. A patterned cap locally enhances 2DEG at the AlN/GaN hetero‐interface due to barrier lowering. It is an additive approach in contrast to the conventional gate recessing technique.