Electric-field-induced refractive index changes in three-step asymmetric coupled quantum wells

A scheme for enhancing the refractive index change Δn in the wavelength region longer than that for an n=1 heavy-hole exciton peak, where the absorption coefficient α is small, is proposed and three-step GaAs/AlGaAs quantum wells (QWs) are numerically analyzed as an example. The basis of this scheme is that an electric-field-dependent oscillator strength can be controlled by designing a QW structure which yields either positive or negative absorption change, Δα at all wavelengths, resulting in an increase in the Δn in the longer wavelength region and a reduction in the operating electric field. The numerical analysis predicts that the electric field for the three-step QW that yields a Δn of ∼10−2 is as small as 5–15 kV/cm which is about one order of magnitude smaller than that for a conventional square-potential QW. In addition, the Δn and the figure-of-merit, which is defined as Δn/α, are larger than those for the conventional QW in the longer wavelength region.