A. Sa'ar

Intersubband electro-absorption and retardation in coupled quantum wells: the role of interface scattering

Abstract In this work we present a systematic experimental study aimed at resolving the various contributions to electro-optical modulation in a multiple coupled quantum wells structure. Using a set of eight-cross/parallel polarizer–analyzer measurements we were able to resolve the spectral dependence of the DC electric-field-induced absorption and phase-retardation due to intersubband transitions. The results of our experiment were fitted to a model that allows all quantum properties of the structure to vary with the external DC electric field and estimate the contribution of each term to the overall modulation. The experimental results suggest that, apart from the Stark shift of the energy levels, a major contribution to electro-optical modulation comes from line width modulation. We propose a model that correlates this effect with alloy disorder and interface roughness scattering that gives rise to electron dephasing. The larger degree of electron localization near the interfaces in the presence of a DC electric field is responsible for this effect.

Modulated resonant Raman and photoluminescence spectroscopy of Bragg confined asymmetric coupled quantum wells

Abstract Electronic Bragg mirrors were used to confine carriers at energy levels above the barrier height in asymmetric coupled quantum wells. Two classes of above barrier states were resolved by using photoluminescence, photoluminescence excitation and modulated resonant Raman spectroscopy. The first class is Bragg confined levels that are highly localized in the asymmetric quantum wells region and are red shifted when locally excited electric field is generated in the asymmetric coupled quantum well region. The second class of levels that extend mainly above the reflectors is not shifted when the locally excited field is generated. This phenomenon is due to the smaller confinement of the extended states in the asymmetric quantum well region.