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

Abstract

The spin structure and spin dynamics of excitons in an ensemble of (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment, containing both direct and indirect band gap dots, are studied. Time-resolved and spectral selective techniques are used to distinguish between the direct and indirect QDs. The exciton fine structure is studied by means of optical alignment and optical orientation techniques in magnetic fields applied in the Faraday or Voigt geometries. A drastic difference in emission polarization is found for the excitons in the direct QDs involving a Γ-valley electron and the excitons in the indirect QDs contributed by an X-valley electron. We show that in the direct QDs the exciton spin dynamics is controlled by the anisotropic exchange splitting, while in the indirect QDs it is determined by the hyperfine interaction with nuclear field fluctuations. The anisotropic exchange splitting is determined for the direct QD excitons and compared with model calculations.c is the maximal circular polarization degree achieved in strong fields, µ B is the Bohr magneton, and g ex is the longitudinal exciton g-factor. The latter is composed of the Γ-electron (g e ) and heavy hole (g hh ) gfactors: g ex = g hh − g e . Both dependencies of ρ l (B) and

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“…A suitable method to observe transitions between k = 0-electrons and Γ-holes, is a resonant PL technique similar, e. g., to that used in Ref. [74] for study of (In,Al)As/AlAs QDs. Fig.…”

Modeling electronic and optical properties of III–V quantum dots—selected recent developments

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On the importance of antimony for temporal evolution of emission from self-assembled (InGa)(AsSb)/GaAs quantum dots on GaP(001)

“…The previous analysis showed an increase of QD recombination times with decreasing energy from 6 ns to 9 ns for S with , of 1.83 eV and 1.80 eV, respectively, and from 2 ns to 6 ns for S cap of energies close to 1.79 eV and 1.73 eV. The slower recombination times might be assigned to indirect momentum transitions, even though, without detailed single dot spectroscopic study [65], this is rather speculative because it could be as well caused by ensemble averaging [66].…”