Design of near lattice-matched AlGaInN-barriers for highly-scalable GaN-based transistor structures

AlGaInN layers at compositions near lattice-matched to GaN have been grown by molecular beam epitaxy. X-ray diffraction and atomic force microscopy show singlephase quaternary layers with smooth morphology. Heterostructures with thin nearly strain-free AlGaInNbarriers exhibit high values for sheet electron density and mobility ranging up to 2.1×1013 cm-2 and 1240 cm2/Vs, respectively. The epitaxial design of the structures comprises a multi-layer spacer which enables a wider separation between channel and barrier compared to a single AlN interlayer and serves as a protection during growth. A series of wafers with varied composition in the barrier reveals that the electron mobility increases with Gacontent in AlGaInN as expected considering the miscibility of quaternary nitrides.