Three Subband Occupation of the Two-Dimensional Electron Gas in Ultrathin Barrier AlN/GaN Heterostructures

Ultrathin barrier AlN/GaN heterostructure with record low sheet resistance of 82 omega sq(-1)is achieved by molecular beam epitaxy, where Shubnikov-de Haas oscillations (SdHOs) and quantum Hall effect (QHE) of two-dimensional electron gas (2DEG) are observed. The fast Fourier transform analysis of the SdHOs demonstrates a three-subband occupation in the triangle quantum well for the first time, with the electron density ofn(1)=2.2x10(13) cm(-2),n(2)= 2.3x10(12)cm(-2), andn(3)=8.8x10(11)cm(-2), respectively, and the corresponding energy of 265, 28, and 11 meV below Fermi level. The three-subband QHE with a superposed feature is also demonstrated for the first time in AlN/GaN heterostructure, with large filling factors at high electron densities. By analyzing the first subband as the dominant part of the superposed QHE, the transport physics of a special magneto-intersubband scattering is revealed. These results contribute to a better understanding of the quantum physics for 2DEG, leading to a versatile functionality for AlN/GaN devices.