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We study the transition from type-I to type-II AlInAs/AlGaAs self-assembled quantum dots (QDs) which is induced by changing the Al composition of an AlGaAs matrix. We found theoretical evidence for type-II band alignment above the crossover Al concentration . For this purpose, we obtained the phase diagram for different QD radii, and we can identify the region where the electron states derived from the X-valley are lower than those derived from the Γ-point. The spatial distribution of electrons and holes is very sensitive to QD size variations. Furthermore, the effect of the QD type on the exciton binding energy is investigated. The ground-state exciton binding energy is always significantly smaller for type-II than for corresponding type-I systems, which originates from the redistribution of the electron and hole wave function. [ABSTRACT FROM AUTHOR]

We investigate the theoretical band structure of organic-inorganic perovskites APbX 3 with tetragonal crystal structure. Using D 4 h point group symmetry properties, we derive a general 16-band Hamiltonian describing the electronic band diagram in the vicinity of the wave-vector point corresponding to the direct band gap. For bulk crystals, a very good agreement between our predictions and experimental physical parameters, as band gap energies and effective carrier masses, is obtained. Extending this description to three-dimensional confined hybrid halide perovskite, we calculate the size dependence of the excitonic radiative lifetime and fine structure. We describe the exciton fine structure of cube-shaped nanocrystals by an interplay of crystal-field and electron-hole exchange interaction (short- and long-range parts) enhanced by confinement. Using very recent experimental results on FAPbBr 3 nanocrystals, we extract the bulk short-range exchange interaction in this material and predict its value in other hybrid compounds. Finally, we also predict the bright-bright and bright-dark splittings as a function of nanocrystal size.