Excitonic spectra of asymmetric, coupled double quantum wells in electric fields

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Abstract
The excitonic spectra of asymmetric, coupled double quantum wells in external electric fields were analyzed by a two-band model in the effective-mass envelope-function approximation. Only bound states exist because we assumed that the potential profile has an infinite potential energy at both ends of the double-quantum-well structure. The absorption spectra were calculated in the dipole approximation for the excitonic and the continuum contributions. The variations of the envelope functions, the eigenenergies, the oscillator strengths, and the absorption spectra with electric fields for symmetric and asymmetric wells are presented. We found that, without fields, the asymmetry of the double-quantum-well structures can yield nonzero oscillator strengths for forbidden transitions, but these are too weak to be important in the absorption spectra. With increasing fields, asymmetries of the well structures can yield entirely different spectra depending on the shifts of the central barrier towards the right side or the left side of the well. Theoretical and experimental results were compared and good agreement was reached.