High mobility two-dimensional electron gases in nitride heterostructures with high Al composition AlGaN alloy barriers

We report high-electron mobility nitride heterostructures with $>70%$ Al composition AlGaN alloy barriers grown by molecular beam epitaxy. Direct growth of such AlGaN layers on GaN resulted in hexagonal trenches and a low mobility polarization-induced charge. By applying growth interruption at the heterojunction, the surface morphology improved dramatically and the room temperature two-dimensional electron gas (2DEG) mobility increased by an order of magnitude, exceeding $1300cm2/Vs$⁠. The 2DEG density was tunable at $0.4–3.7×1013/cm2$ by varying the total barrier thickness $(t)$⁠. Surface barrier heights of the heterostructures were extracted and exhibited dependence on $t$⁠.