Correlation between threading dislocation density and sheet resistance of AlGaN/AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy

AlGaN/AlN/GaN heterostructures were grown on 6H-SiC, GaN-on-sapphire, and free-standing GaN, resulting in heterostructures with threading dislocation densities of ∼2 × 1010, ∼5 × 108, and ∼5 × 107 cm−2, respectively. Growths were carried out under Ga-rich conditions by plasma-assisted molecular beam epitaxy to determine the influence of threading dislocation density on the sheet resistance of AlGaN/AlN/GaN heterostructures. High threading dislocation density was observed to significantly degrade Hall mobility. An AlGaN/AlN/GaN heterostructure with a ∼2 nm AlN interlayer and a threading dislocation density of ∼5 × 107 cm−2 achieved the very low room temperature sheet resistance of 175 Ω/□.