ELECTRIC-FIELD-INDUCED REFRACTIVE-INDEX CHANGES IN 3-STEP ASYMMETRIC COUPLED QUANTUM-WELLS

A scheme for enhancing the refractive index change DELTAn in the wavelength region longer than that for an n = 1 heavy-hole exciton peak, where the absorption coefficient alpha 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, DELTAalpha at all wavelengths, resulting in an increase in the DELTAn 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 DELTAn of approximately 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 DELTAn and the figure-of-merit, which is defined as DELTAn/alpha, are larger than those for the conventional QW in the longer wavelength region.