Growth and Characterization of Nitrogen‐Polar AlGaN/AlN Heterostructure for High‐Electron‐Mobility Transistor

A nitrogen‐polar (N‐polar) AlGaN/AlN high‐electron‐mobility transistor (HEMT) is proposed, and the generation of a 2D electron gas (2DEG) is simulated. The band diagram of N‐polar (Al)GaN/AlN shows the generation of the 2DEG, whereas that of the conventional metal‐polar (Al)GaN/AlN structure shows the generation of a 2D hole gas. Furthermore, the concentration of the 2DEG is considerably high even when the (Al)GaN layer is as thin as a few nanometers. N‐polar AlGaN/AlN is grown on sapphire substrates with a misorientation angle of 2°; furthermore, atomic force microscope measurements in a range of 5 × 5 μm 2 demonstrate that the root‐mean‐square value obtained from atomic force microscopy of N‐polar AlGaN is approximately 0.7 nm. N‐polar AlGaN layers with a thickness of approximately 40–60 nm with more than 50% Al content are almost coherently grown on the N‐polar AlN layer with a thickness of approximately 400 nm.