Turn-on voltage engineering and enhancement mode operation of AlGaN/GaN high electron mobility transistor using multiple heterointerfaces

A novel device design for enhancement mode operation of III-nitride high electron mobility transistor (HEMT) structure has been proposed and demonstrated. The proposed HEMT device structure consists of a multi-heterojunction (SiO2/AlxGa1−xN/GaN/AlyGa1−yN) design in contrast to a single AlGaN/GaN heterojunction commonly used in conventional III-nitride HEMT designs. Normally OFF operation of the proposed HEMT design is expected to take place for thicker GaN and the top AlxGa1−xN layers than previously allowed. The effects of design parameters on the value of the device turn ON voltage have been studied extensively using simulations. Various device structures have been developed based on the simulations results and epitaxially grown by MOCVD. I–V measurements support the effects of design parameters on the turn ON voltage predicted by the simulations and have confirmed the enhancement mode operation.