Exciton Fine Structure in Axially Symmetric Quantum Dots and Rods of III-V and II-VI Semiconductors.

Both absorption and emission of light in semiconductor quantum dots occur through excitation or recombination of confined electron-hole pairs, or excitons, with tunable size-dependent resonant frequencies that are ideal for applications in various fields. Some of these applications require control over quantum dot shape uniformity, while for others, control over energy splittings among exciton states emitting light in different polarizations and/or between bright and dark exciton states is of key importance. These splittings, known as exciton fine structure, are very sensitive to the nanocrystal shape.

Effect of shape anisotropy in nanocrystals of semiconductors with small spin-orbit splitting.

We derive an effective spin-Hamiltonian accounting for the shape anisotropy of the zinc blende semiconductor nanocrystals within the k · p formalism explicitly taking into account the spin-orbit split-off valence band. It is shown that, for small InP nanocrystals, neglect of the spin-orbit split-off band can lead to significant underestimation of one of the two parameters determining the exciton fine-structure splittings. This parameter is only important for nanocrystals with shape anisotropy.

Revealing the Band-Edge Exciton Fine Structure of Single InP Nanocrystals.

We investigate the fundamental optical properties of single zinc-blende InP/ZnSe/ZnS nanocrystals (NCs) using frequency- and time-resolved magneto-photoluminescence spectroscopy. At liquid helium temperature, highly resolved spectral fingerprints are obtained and identified as the recombination lines of the three lowest states of the band-edge exciton fine structure. The evolutions of the photoluminescence spectra and decays under magnetic fields show evidence for a ground dark exciton level 0 with zero angular momentum projection along the NC main elongation axis.

Carrier confinement and interband optical transitions in lead chalcogenide quantum wells, nanosheets, and nanoplatelets.

Analytic equation for energy dispersion of electronic states in lead chalcogenide nanosheets is derived within an effective mass model. Selection rules for interband optical transitions are analyzed and expressions for interband optical matrix elements are obtained. It is shown that the main effect of the lateral confinement in nanoplatelets can be accounted for in terms of the quantized in-plane wave vector.