Enhanced 2DEG confinement in GaN-based HEMTs: Exploring the role of AlGaN back barriers through Schro<spacing diaeresis>dinger - Poisson simulations and experimental validation

A systematic investigation, combining simulations and experimental evaluations, for the design of double heterostructures AlxGa1-xN/GaN/AlyGa1-yN and AlN/GaN/AlyGa1-yN high electron mobility transistor (DH-HEMT) structures on a Ga-face GaN (0001) buffer layer on Si (111) substrate, is presented. Self-Consistent Schro<spacing diaeresis>dingerPoisson (SCSP) calculations were implemented for a wide range of composition and thickness values of the AlyGa1-yN back barrier, for the case of an 150 nm GaN channel layer and a top-barrier consisting of either a conventional 30 nm AlGaN (24% AlN) or a 3 nm AlN layer. The SCSP calculations demonstrated the formation of a high energy barrier (2.5-3.0eV) for the transfer of electrons between the channel and the GaN buffer layer/ substrate and negligible electron accumulation in the GaN buffer layer, at the bottom AlGaN/GaN interface, when the thickness of the AlGaN back barrier was approximately one-third of the thickness of the GaN channel layer, and the AlN content in the AlGaN alloy of the back barrier was relatively low, not exceeding 10%. The results are explored for the implementation of very thin body AlN/GaN HEMTs on Si (111) by plasma-assisted molecular beam epitaxy. Structures with AlGaN back barriers containing 8% and 30% AlN exhibited similar open channel currents but threshold voltages of -1.2V and -14V, respectively.