Magnetointersubband Oscillations of the Two-Dimensional Electron Gas in Al_xGa_1-xN/GaN Heterostructures

Shubnikov-de Haas (SdH) measurements are performed over a temperature range of 1.5-20 K in Al_0.22Ga_0.78N/GaN heterostructures with two subbands occupied. In addition to an intermodulation between two sets of SdH oscillations from the first and second subbands, a beating in oscillatory magnetoresistance at 12 K is observed, due to the mixing of the first subband SdH oscillations and `magnetointersubband' (MIS) oscillations. A phase shift of π between the SdH and MIS oscillations is also clearly identified. Our experimental results, i.e. that the SdH oscillations dominate at low temperature and MIS oscillations dominate at high temperature, fully comply with the expected behaviour of MIS oscillations.