Temperature-dependent magnetotransport measurements have been carried out on high-quality two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures with different Al content grown on sapphire substrates. The GaN electron effective mass and the quantum scattering time are determined by well-resolved Shunbikov-de Hass oscillations. The electron effective mass is determined to be 19m0. The ratio of the classic scattering time to the quantum scattering time increases with increasing 2DEG sheet carrier density, which agrees very well with the previous calculation based on an ideal 2DEG in conventional semiconductor systems. Our result indicates that a low density of deep centers results in the much higher mobility of our structure compared with other reports, which is of critical importance in fabricating a high-quality 2DEG structure in AlGaN/GaN systems.
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