Optical studies of structural and magnetic anisotropies in epitaxial CdSe/ZnSe quantum dots

Abstract

We summarize experimental studies on the optical polarization properties of MBE-grown shape-asymmetric self-assembled CdSe/ZnSe quantum dots (QDs). The zero magnetic field fine structure splitting of excitonic transitions in structurally anisotropic QDs gives rise to an effective linear-to-circular and circular-to-linear optical polarization conversion upon resonant excitation of the QD ensemble. The effect is qualitatively modelled in terms of a pseudospin formalism. Furthermore, we show how an in-plane magnetic field leads to a complex rotation behavior of the axis of the optical polarization. Our analysis based on the exciton pseudospin Hamiltonian unambiguously displays that these effects are induced by isotropic and anisotropic contributions to the heavy hole Zeeman term. Likewise we show that the latter mechanism can be used to tune the optical respone of shape-anisotropic QDs such that the optical polarization properties are equal to QDs of perfect D 2d symmetry.

Angular harmonics of the excitonic polarization conversion effect

“…4,5 Reciprocal conversions of the linear and the circular polarizations were found to occur even without any magnetic field applied. 6,7 The 'swings of optical alignment' were observed. 8 Lately, very efficient polarization conversions by single quantum dots were reported.…”

“…8 Lately, very efficient polarization conversions by single quantum dots were reported. 9,10 Incidentally, the recent experimental studies [6][7][8][9][10] widely exploited the method of angular harmonics of polarization, where the sample was rotated about the growth axis while the polarization responses (various conversions) were studied in their dependency on the rotation angle ϕ . This fact motivated us to undertake an explicit analysis of possible ϕ -dependences of the polarization responses -in more general terms than it has been attempted in Ref.…”