Optically detected cyclotron resonance of GaAs quantum wells: Effective-mass measurements and offset effects

We have detected cyclotron resonance in a series of undoped GaAs quantum wells by modulating the photoluminescence intensity with far-infrared radiation. The conduction-band mass was measured for different quantum-well widths, and good agreement with a simple formula based on k⋅p theory is achieved. An offset was observed in the cyclotron-resonance energy, strongly dependent on well width. The interpretation is that monolayer-width fluctuations localize the carriers, giving an additional binding energy to the cyclotron-resonance transition.