Spin-flip Raman scattering of theΓ−Xmixed exciton in indirect band gap (In,Al)As/AlAs quantum dots

Abstract

The band structure of type-I (In,Al)As/AlAs quantum dots with band gap energy exceeding 1.63 eV is indirect in momentum space, leading to long-lived exciton states with potential applications in quantum information. Optical access to these excitons is provided by mixing of the -and X-conduction-band valleys, for which their spins may be oriented by resonant spin-flip Raman scattering. This access is used to study the exciton spin-level structure by accurately measuring the anisotropic hole and isotropic electron g factors. The spin-flip mechanisms for the indirect exciton and its constituents as well as the underlying optical selection rules are determined. The spin-flip intensity is a reliable measure of the strength of -X-valley mixing, as evidenced by both experiment and theory.

Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment

“…Note that for small values of ∆E ΓX an admixing of Γ and X-electron states takes place [8]. However, the effect of this admixing on the exciton fine structure is not in the focus of this paper.…”

“…We will specify these QDs as the indirect QDs. It was shown that due to inhomogeneous broadening an ensemble of (In,Al)As/AlAs QDs is composed of direct and indirect dots, whose emissions are partly overlapping [6][7][8]10]. As we will show below, the direct and indirect QDs can be well distinguished from each other by different optical techniques.…”

“…Finally we note that the magnitude of the anisotropic exchange interaction in indirect QDs is at least smaller than δ max = 1 /2B N µ B g ex , otherwise, the optical orientation in these QDs will be destroyed by the mixing of exciton states. Taking into account that B 1/2 of the Hanle curve should be equal to B N and g ex for indirect exciton in (In,Al)As/AlAs QDs equals to 0.43 [8] we can estimate the upper limit of the exchange splitting for an exciton Calculation of δ1 for the direct exciton in (In,Al)GaAs/AlAs QD as a function of QD height for lens, pyramid, and truncated cone shaped QDs with an In content either of 0.7 set constant in the whole QD volume or linearly increasing along the dot vertical symmetry axis from 0.65 at QD base to 0.85 at QD apex. In all cases the QD base diameter was fixed to 15 nm.…”

Single and Double Electron Spin-Flip Raman Scattering in CdSe Colloidal Nanoplatelets

“…In low-dimensional structures the SFRS intensity is drastically increased by the presence of resident quantum-confined electrons that interact with photogenerated excitons. [21][22][23] In this paper we use the spin-flip Raman scattering technique to study the spin properties of CdSe colloidal nanoplatelets. By measuring ensembles of NPLs having various orientations in the Faraday and Voigt geometries of the external magnetic field and analyzing the polarization properties of the Raman spectra we determine the electron g-factor and its anisotropy.…”

Spin dynamics and magnetic field induced polarization of excitons in ultrathin GaAs/AlAs quantum wells with indirect band gap and type-II band alignment

“…Due to the large band gap at the X point, the spin-orbit contribution to the electron g factor is vanishingly small [16,22]. As a result, the electron g factor, g e , is isotropic and its value almost coincides with the free-electron Landé factor of +2.0 [23]. The recombination times of the bright and dark excitons were unambiguously determined in Ref.…”