Resonant subband Landau level coupling in GaAs-(Ga,Al)As quantum wells in tilted magnetic fields

Far-infrared transmission measurements are reported for GaAs-(Ga,Al)As quantum wells of widths 100.0 nm, 30.0 nm and 10.0 nm in magnetic fields of up to 20 T, tilted away from the normal to the quantum well plane by angles of up to theta =50 degrees . Deviations of the cyclotron resonance field from a cos theta law, valid for purely two-dimensional systems, are consistent with a coupling of Landau level and electric subband quantizations by a tiled magnetic field. The varied subband structure of the quantum wells allows access to regimes where the subband separation is less than, comparable to, or much greater than the cyclotron splitting. The shifts in resonant field position are compared with theoretical models, which are found to overestimate the strength of the coupling between the subband and Landau level quantizations. The technique of tilted-field cyclotron resonance is shown to be a method of probing the band bending of a quantum well using asymmetric doping, etc.