Second harmonic electroreflectance study of AlGaAs-GaAs asymmetric triangular and coupled double quantum wells

Electroreflectance (ER) spectroscopy is used to study AlGaAs-GaAs asymmetric triangular and coupled double quantum wells. The ER spectra are taken at both the fundamental (If) and second harmonic (2f ) modulation frequencies. A detailed ER lineshape analysis appropriate for a Lorentzian dielectric function is presented. The experimental If and 2f spectra are, respectively, shown to be related to the first and second order field induced changes in the dielectric function. A detail comparison of the line shapes of the If, 2f and energy derivative of the If spectra and their respective spectral forms enable a qualitative deduction of the dominant mechanism of the experimental ER spectra. In particular, for the asymmetric triangular well structure, the dominance of excitonic modulation mechanism can be inferred. Useful additional information on the sample signature such as the features associated with the red and blue shifts are obtained through such a comparative study. In addition, several weak features are observed to be significantly enhanced in the 2f spectra and the characteristics of these features are deduced.