Modified five-layer asymmetric coupled quantum well (M-FACQW) for giant negative refractive index change

We have analyzed the electrorefractive properties of a GaAs/AlGaAs modified five-layer asymmetric coupled quantum well (M-FACQW). The theoretical analyses show that the M-FACQW is expected to exhibit a giant negative electrorefractive index change Δn in the transparent-wavelength region away from the absorption edge. The influence of fluctuations in layer thickness on the electrorefractive properties of the M-FACQW was also investigated. Although the fluctuation in layer thickness deteriorates the characteristics of Δn in the M-FACQW, the M-FACQW still maintains a very giant Δn compared with that of a conventional rectangular quantum well without thickness fluctuation. In addition, we have fabricated the M-FACQW with monolayer accuracy by solid-source molecular beam epitaxy, and measured its photoabsorption current. The experimental results are in good agreement with the calculated properties. This indicates that the M-FACQW has great potential for use in ultra-wideband and low-voltage optical modulators and switches.