A theory for the electroreflectance spectra of quantum well structures

A theory is presented to model the lineshape observed in electroreflectance spectra of quantum well structures reported recently by the authors and elsewhere. The existence of such spectra is shown to be a direct consequence of the sensitivity to a perpendicular electric field of the quantum well sub-band energies and the mechanism is thus qualitatively different from the Franz-Keldysh effect, which may explain the electroreflectance spectra of bulk materials. The importance of optical interference in determining the observed lineshape in multilayer samples is emphasised, and good agreement is obtained between the observed spectrum and the spectrum predicted by the model of a single 100 AA quantum well of Ga_0.8Al_0.2As/GaAs/Ga_0.8Al_0.2As. From a careful analysis of absorption, photoluminescence excitation and electroreflectance spectra for this sample the authors calculate binding energies for the heavy and light hole excitons of 11.6+or-1.3 meV and 10.1+or-1.1 meV respectively.