GaN-based high-electron-mobility transistor structures with homogeneous lattice-matched InAlN barriers grown by plasma-assisted molecular beam epitaxy

Metal-polar In_0.17Al_0.83N barriers, lattice-matched to GaN, were grown under N-rich conditions by plasma-assisted molecular beam epitaxy. The compositional homogeneity of these barriers was confirmed by plan-view high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. Metal-polar In_0.17Al _0.83N/(GaN)/(AlN)/GaN structures were grown with a range of AlN and GaN interlayer (IL) thicknesses to determine the optimal structure for achieving a low two-dimensional electron gas (2DEG) sheet resistance. It was determined that the presence of a GaN IL was necessary to yield a 2DEG sheet density above 2 × 10¹³ cm^-2. By including AlN and GaN ILs with thicknesses of 3 nm and 2 nm, respectively, a metal-polar In _0.17Al_0.83N/GaN/AlN/GaN structure regrown on a GaN-on-sapphire template yielded a room temperature (RT) 2DEG sheet resistance of 163 Ω/□. This structure had a threading dislocation density (TDD) of ∼5 × 10⁸ cm^-2. Through regrowth on a free-standing GaN template with low TDD (∼5 × 10⁷ cm ^-2), an optimized metal-polar In_0.17Al_0.83N/ GaN/AlN/GaN structure achieved a RT 2DEG sheet resistance of 145 Ω/□ and mobility of 1822 cm² V^-1 s^-1. High-electron-mobility transistors with output current densities above 1 A mm^-1 were also demonstrated on the low-TDD structure.