Collective cyclotron resonance in a quasi-three-dimensional electron gas

Far-infrared magnetotransmission measurements are carried out on modulation-doped wide parabolic Alₓ{Ga}_{1{{-}}x}$As quantum wells. We report the first observation of plasma-shifted cyclotron resonance in a semiconductor space-charge layer. The bulk carrier density deduced from the plasma frequency is found to be independent of the areal electron density. The homogeneity of the three-dimensional electron density is probed using this new resonant mode.