Polarization rotation in asymmetric semiconductor quantum dots

Abstract

Rotation of input polarization arising due to the recombination of electrons from the 1s-excitonic state to the hybrid valence band states have been theoretically examined in asymmetric semiconductor quantum dots. The Jones matrix calculations suggest that the polarization rotation directly depends on the asymmetry of the quantum dot and strength of hh-lh coupling. The results advocate the suitability of quantum dots as polarizing devices. IntroductionSemiconductor quantum dots (QDs) with sizes in the range of a few tens of nanometers have attracted much attention as possible candidate materials for quantum information processing [1,2]. The discrete and spin degenerate electronic energy levels of these QDs make them successful to manifest quantum coherence. Excitations corresponding to a specific spin state in a symmetric QD can be monitored by using suitable polarized light [3,4] and establish the QDs as useful hosts for the realization of quantum bits [5]. Symmetry plays an important role in determining the electronic spectra of QDs. According to the point symmetry C 2v in zinc blende based heterostructures, the interface induced hh-lh coupling is allowed and results in anisotropic exchange splitting of the excitonic levels. The in-plane symmetry is also lifted in a QD due to its shape and size anisotropy and adds to the exchange splitting [6][7][8]. The asymmetry in QDs is also responsible for (a) band mixing phenomenon [9,10], (b) spin splitting [4,11] and (c) modification in selection rules [12,13]. These phenomena are manifested in the experimental observations of the size and shape dependent polarization luminescence obtainable from the QDs. It is widely accepted that the electron-hole exchange interaction (EHEXI) causes coupling of jþ1i and jÀ1i optically active heavy hole exciton states and results in complex linear polarization of split fine structure components [14]. In zero magnetic field, the polarized luminescence appears as a result of optical spin orientation. The conservation of spin in photoabsorption allows spin orientation of excitons by polarized light beams and in effect exhibits