Asymmetry of localised states in a single quantum ring: Polarization dependence of excitons and biexcitons

Abstract

We performed spectroscopic studies of a single GaAs quantum ring with an anisotropy in the rim height. The presence of an asymmetric localised state was suggested by the adiabatic potential. The asymmetry was investigated in terms of the polarization dependence of excitons and biexcitons, where a large energy difference (∼ 0.8 meV) in the exciton emission energy for perpendicular polarizations was observed and the oscillator strengths were also compared using the photoluminescence decay rate. For perpendicular polarizations the biexciton exhibits twice the energy difference seen for the exciton, a fact that may be attributed to a possible change in the selection rules for the lowered symmetry. * Electronic address: kskyhm@pusan.ac.kr † Electronic address: r.taylor1@physics.ox.ac.uk

Quasi-one-dimensional density of states in a single quantum ring

“…X n =2 becomes also suppressed as the temperature increases. We have already shown17 that the p  − orbital asymmetry of X n =2 gives rise to a large polarization asymmetry and a broad linewidth as a consequence of the strong coupling with phonon bath compared to X n =1 . Intermediate spectra between X n =1 and X n =2 , where the finely-spaced levels of a ring structure with sub-meV spacing might be seen, are extremely weak.…”

“…1(a)) is not significant, the spectral inhomogeneity of ensemble QRs is quite broad due to the anisotropic volcano-like morphology, where the energy ranges from the bandgap of bulk GaAs up to that of AlGaAs. In this case, it was known that the wavefunction is likely to be localized in a crescent-like shape, but the degree of localization depends on the QR morphology1720. The emission near the barrier originates from a strongly localized state in the QR.…”

“…When the substrate temperature reached 200 °C, arsenic tetramers were introduced to form GaAs rings. Finally, the rings were capped with 60 nm-thick Al 0.3 Ga 0.7 As and 3 nm-thick GaAs for optical measurements1718. During ring formation, the flux of Ga is equivalent to a GaAs growth rate of 0.5 monolayer/s, and the flux of arsenic is 1.2 × 10 −7 Torr.…”

“…When a volcano-like rim anisotropy is present1112131415, the wavefunction becomes localized with a crescent-like shape161718. Provided that the degree of localization is moderate, rotational motion of an exciton around the whole circumference can be possible through tunneling.…”

Polarization anisotropy of exciton in self-assembled elliptical InP/InGaP quantum dots

“…From a single QD spectroscopy, it was known that d XY can increase from 0.1 meV up to~0.4 meV as the anisotropy is enhanced by strain and shape control [22,5]. In this case, the linear polarization of jX〉 and jY〉 are perpendicular to each other.…”