Excited exciton and biexciton localised states in a single quantum ring

Abstract

We observe excited exciton and biexciton states of localised excitons in an anisotropic quantum ring, where large polarisation asymmetry supports the presence of a crescent-like localised structure. We also find that saturation of the localised ground state exciton with increasing excitation can be attributed to relatively fast dissociation of biexcitons (? 430 ps) compared to slow relaxation from the excited state to the ground state (? 1000 ps). As no significant excitonic Aharonov-Bohm oscillations occur up to 14 T, we conclude that phase coherence around the rim is inhibited as a consequence of height anisotropy in the quantum ring.Comment: 4 pages, 4 figure

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

“…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.…”

Optically Induced Long‐Range Coupling Studies in a Single GaAs Laterally Coupled Quantum Dot

“…Our magneto‐PL spectra show both Zeeman splitting by spin directions to magnetic field ( B ) (direction parallel to B , direction opposite of B ), and diamagnetic shifts when the magnitude of magnetic fields increased. In particular, we can obtain the diamagnetic coefficients ( γ ) by the definition γ , where the γ value of coupled bi‐exciton state is extremely large in Figure b, after comparison with those of localized bi‐exciton states. It is known that these diamagnetic coefficients are proportional to the wave function area; therefore, a larger γ from a coupled bi‐exciton state means that the wave function is extended across both QD 1 and QD 2 by the optical coupling procedure.…”

Decoherence Dynamics of Localized States in a Single GaAs/AlGaAs Quantum Ring

“…Results and Discussion : As shown schematically in Figure (a), excitons in a QR are likely localized in a crescent‐shape due to the height anisotropy although ring structures are clearly seen in AFM image of Figure (b). As the vertical height (≈4 nm) is far smaller than the ring diameter (≈40 nm), the fast varying vertical wavefunction can be separated from the slowly varying lateral part by the adiabatic approximation.…”

“…However, an internal decoherence mechanism in a GaAs QR also needs to be considered. Although the terminology of ring reminds an ideal isotropic structure, the morphology of droplet QRs shows a volcano‐like structure, where height anisotropy and lateral ellipticity are seen. In this case, anisotropic potential valleys are given in a single QR.…”