Exchange enhancement of spin-splitting in Al_xGa _1-xN/GaN heterostructures in tilted magnetic fields

Al_xGa_1-xN/GaN heterostructures are investigated by magnetotransport experiments in tilted magnetic fields at low temperatures. The spin-split peaks of the Shubnikov-de Haas (SdH) oscillations are observed at high magnetic fields, which are attributed to the Zeeman spin-splitting of the two-dimensional electron gas at the heterointerface. The exchange enhanced g* of the spin-splitting is investigated by measuring the positions of the pairs of spin-split SdH maxima. Moreover, it is found that g* becomes smaller with the increasing tilt angle, which suggests the anisotropy of g* is due to the strong polarization-induced electric field at the Al _xGa_1-xN/GaN heterointerface.