Cyclotron Resonance in ZnO Heterostructures at High Magnetic Fields

The carrier-density dependence of the cyclotron resonance was studied in ZnMgO/ZnO heterostructures between n=5.4×10¹² cm^?2 and n=7.5×10¹² cm^?2. The effective mass was obtained as m ^?=0.32m ₀, and the significant carrier-density dependence of the effective mass was not observed in the present samples. This is partially due to the suppression of the resonant polaron effect in the dense carrier system. Oscillatory behavior appears in the cyclotron resonance spectra at the higher magnetic field side of the resonant field. The oscillatory period is perfectly coincident with the one of the Shubnikov-de Hass oscillation.