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Low-temperature magnetotransport measurements were performed on an Al0.25Ga0.75N/GaN two-dimensional electron system. In this system, we observe Shubnikov-de Haas (SdH) oscillations in a perpendicular magnetic field B. By measuring the positions of a pair of spin-split SdH maxima, we are able to estimate the g-factors at different Landau level (LL) indices. We find the g-factor is enhanced over its bulk value in GaN (≅2) due to many-body exchange interactions. Moreover, the measured g-factor increases with decreasing LL index, indicating that many-body electron–electron interactions become stronger as the number of occupied LLs decreases. Our results suggest that the exchange energy Eex shows an approximately linear B dependence. [ABSTRACT FROM AUTHOR]

We report the drastic enhancement pattern of Shubnikov-de Haas (SdH) oscillations observed in an AlGaN/GaN heterostructure by microwave modulation. The dependence of the SdH pattern on microwave power and temperature is investigated. The underlying mechanism is attributed to the effect of carrier heating. This technique helps study the transport properties of two-dimensional electrons in many wide-band-gap heterostructures, in which moderate mobilities and heavier electron effective mass (rapidly damping SdH amplitudes) are frequently encountered. In addition, this method has the advantage of keeping the carrier concentration fixed and not requiring expensive high-energy laser facilities compared with carrier-modulated SdH measurements. [ABSTRACT FROM AUTHOR]