Strain-induced polarization of AlN/GaN heterointerfaces enabling ultra-high 2DEG densities

Abstract

The strong polarization fields present at the AlN/GaN heterointerface make them an attractive candidate for the development of high electron mobility transistors (HEMTs) with high current densities. In this work, we report exceptionally high two-dimensional electron gas (2DEG) density in AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy. The sample with a 9 nm AlN barrier, near the onset of relaxation, yields a maximum 2DEG density of ∼1.3 × 1014 cm−2, more than 2× larger than previously reported values, while the fully strained 6 nm barrier exhibits ∼7.8 × 1013 cm−2 with superior crystalline quality. Additionally, the sheet resistance values reported in this work are below 200 Ω/□ at 2DEG densities approaching 1014 cm−2. These results highlight the critical role of strain–polarization coupling in achieving extreme carrier confinement, establishing benchmarks for III-nitride HEMTs and future wide-bandgap electronics.