Inhibited carrier transfer in ensembles of isolated quantum dots

We report significant differences in the temperature-dependent and time-resolved photoluminescence (PL) from low and high surface density InxGa1-xAs/GaAs quantum dots (QDs). QD's in high densities are found to exhibit an Arrhenius dependence of the PL intensity, while low-density (isolated) QD's display more complex temperature-dependent behavior. The PL temperature dependence of high density QD samples is attributed to carrier thermal emission and recapture into neighboring QD's. Conversely, in low density QD samples, thermal transfer of carriers between neighboring QD's plays no significant role in the PL temperature dependence. The efficiency of carrier transfer into isolated dots is found to be limited by the rate of carrier transport in the InxGa1-xAs wetting layer. These interpretations are consistent with time-resolved PL measurements of carrier transfer times in low and high density QD's. [S0163-1829(99)04748-7]

The dark exciton ground state promotes photon-pair emission in individual perovskite nanocrystals

Cesium lead halide perovskites exhibit outstanding optical and electronic properties for a wide range of applications in optoelectronics and for light-emitting devices. Yet, the physics of the band-edge exciton, whose recombination is at the origin of the photoluminescence, is not elucidated. Here, we unveil the exciton fine structure of individual cesium lead iodide perovskite nanocrystals and demonstrate that it is governed by the electron-hole exchange interaction and nanocrystal shape anisotropy. The lowest-energy exciton state is a long-lived dark singlet state, which promotes the creation of biexcitons at low temperatures and thus correlated photon pairs. These bright quantum emitters in the near-infrared have a photon statistics that can readily be tuned from bunching to antibunching, using magnetic or thermal coupling between dark and bright exciton sublevels

Self-organized quantum rings:physical characterization and theoretical modeling

\u3cp\u3eAn adequate modeling of self-organized quantum rings is possible only on the basis of the modern characterization of those nanostructures. We discuss an atomic-scale analysis of the indium distribution in self-organized InGaAs quantum rings (QRs). The analysis of the shape, size and composition of self-organized InGaAs QRs at the atomic scale reveals that AFM only shows the material coming out of the QDs during the QR formation. The remaining QD material, as observed by Cross-Sectional Scanning Tunneling Microscopy (X-STM), shows an asymmetric indium-rich crater-like shape with a depression rather than an opening at the center and determines the observed ring-like electronic properties of QR structures. A theoretical model of the geometry and materials properties of the self-organized QRs is developed on that basis and the magnetization is calculated as a function of the applied magnetic field. Although the real QR shape differs strongly from an idealized circular-symmetric open-ring structure, Aharonov-Bohm-type oscillations in the magnetization have been predicted to survive. They have been observed using the torsion magnetometry on InGaAs QRs. Large magnetic moments of QRs are shown to originate from dissipationless circulating currents in the ground state of an electron or hole in the QR. Examples of prospective applications of QRs are presented that do and do not utilize the topological properties of QRs.\u3c/p\u3