Excitons in Asymmetric Nanostructures: Confinement Regime

Abstract

Quantum confinement of electrons and holes in semiconductor nanostructures results in quantization of their energy levels with level spacing generally decreasing with the confinement length. The relation between these splittings and the energy of the electron-hole Coulomb interaction may serve as a measure of exciton confinement regime. We consider theoretically strongly in-plane asymmetric nanostructures, like InAs/AlGaInAs elongated quantum dots. Based on optical properties, we find a possible indication of coexistence of different confinement regimes for the two bright exciton states that couple to light polarized along the two nonequivalent axes distinguished by the structural asymmetry. Exciton lifetimes and their distinct dependences on energy derived here for the two confinement regimes are in good agreement with those of recently measured double exponential photoluminescence decays. Additionally, for highly elongated dots, one of the states exhibits properties typical for the weak confinement regime, which may have a significant impact on spin relaxation processes.

Optical and electronic properties of low-density InAs/InP quantum-dot-like structures designed for single-photon emitters at telecom wavelengths

“…Recent studies have provided explanation of some of their properties, such as partially polarized emission [14], exciton recombination characterized by two distinct lifetimes in the case of asymmetric dots [15] or the structure of excited states [16]. They have also raised a question regarding the exciton confinement regime [17,18]. These results were, however, obtained mostly for very dense ensembles of elongated QDs [19], and thus characterization of carrier confinement and the resulting optical properties of low-density QDs, growing in a different geometry such as those considered here, is needed.…”

Atypical dependence of excited exciton energy levels and electron-hole correlation on emission energy in pyramidal InP-based quantum dots

“…For generic nanostructures it is adequate to use another definition formulated in terms of relationship between the Coulomb interaction energy and electron/hole energy splittings, and : However, it is still rather natural to identify the gradation of confinement strength with the increasing size, i.e., the volume, of the quantum dot even if its shape is far from spherical. Here, we would like to emphasize the importance of the formulation in terms of energy, as the geometric intuition fails in the presence of anomalous dependence of splittings on QD height, as discussed above, or for large QD asymmetry when a mixed confinement regime is found 36 .…”

Dark-bright excitons mixing in alloyed InGaAs self-assembled quantum dots

“…However, this applicability strongly depends on ability to understand and control the details of excitonic spectra, so-called "excitonic fine structure". [8] On the one hand, the bright exciton spectrum is strongly determined by quantumdot symmetry properties [18][19][20][21][22][23][24][25][26][27][28][29] with extensive efforts [30][31][32][33][34][35][36][37][38][39][40][41][42][43] aimed at reduction of the bright exciton splitting (BES). On the other, the dark exciton fine structure has been studied to a far lesser degree.…”