Wigner molecules and charged excitons in near-field magnetophotoluminescence spectra of self-organized InP/GaInP quantum dots

摘要

We used high-spatial-resolution, low-temperature near-field scanning optical microscopy (NSOM) operatingat magnetic fields B = 0–10 T to study the effects of Wigner localization (WL) on emission spectra ofsingle self-organized InP/GaInP quantum dots (QDs) and investigate the stability of singly (trion) and doubly(tetron) charged exciton complexes in the weak quantum confinement regime. Using NSOM measurementstogether with configuration interaction calculations, we identify the dots having different electron populationN(N = 1–12), quantum confinement (h_(ω0) = 0.6–8 meV) and size D(D = 70–170 nm). For N = 2, we observeda magnetic-field-induced molecular-droplet transition, accompanied by the decomposition of the tetron into aWigner molecule complex (WMC), and the activation of rotovibronic structure. For N = 1, unusually strongvibronic structure resulting from a trion-type WMC was observed. We have shown that magnetic-field-inducedshifts of this structure allowmeasurement of single particle Fock-Darwin levels and angular momentum transitionsof the WMC. In addition, we demonstrated the use of NSOM imaging to probe the charge density distributionand observed anomalous dependence of the image size on the quantum confinement, implying a pairing ofelectrons or formation of whispering gallery modes in the QD. We demonstrated that InP/GaInP QDs, providea Wigner-Seitz radius (r_s ) up to 13, and that the measurements of NSOM magneto-optical spectroscopy usingthese dots makes it possible to study effects arising from strong Coulomb interaction of a few confined electrons(holes).