Topic
Exciton
About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.
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TL;DR: The surace structure gives rise to lateral quantum-size effects which result in increased exciton continuum energies, in strong exciton-phonon interaction, and in pronounced optical anisotropy.
Abstract: We report on the direct synthesis of superlattices with lateral corrugation of the interfaces on (211), (311), and (111) GaAs substrates by moelcular-beam epitaxy. Reflection electron diffraction directly shows the formation of arrays of macrosteps during epitaxial growth. High-resolution transmission electron microscopy confirms the transfer of the surface structure to the GaAs/AlAs interface which results in distinct energy shifts in the luminescence of GaAs/AlAs multilayer structures. The surace structure gives rise to lateral quantum-size effects which result in increased exciton continuum energies, in strong exciton-phonon interaction, and in pronounced optical anisotropy.
216 citations
TL;DR: In this paper, the authors present a theory of optical absorption by interlayer excitons in a heterobilayer formed from transition metal dichalcogenides, which accounts for the presence of small relative rotations that produce a momentum shift between electron and hole bands located in different layers and a moir\'e pattern in real space.
Abstract: We present a theory of optical absorption by interlayer excitons in a heterobilayer formed from transition metal dichalcogenides. The theory accounts for the presence of small relative rotations that produce a momentum shift between electron and hole bands located in different layers, and a moir\'e pattern in real space. Because of the momentum shift, the optically active interlayer excitons are located at the moir\'e Brillouin zone's corners, instead of at its center, and would have elliptical optical selection rules if the individual layers were translationally invariant. We show that the exciton moir\'e potential energy restores circular optical selection rules by coupling excitons with different center of mass momenta. A variety of interlayer excitons with both senses of circular optical activity, and energies that are tunable by twist angle, are present at each valley. The lowest energy exciton states are generally localized near the exciton potential energy minima. We discuss the possibility of using the moir\'e pattern to achieve scalable two-dimensional arrays of nearly identical quantum dots.
215 citations
TL;DR: Two single-dot spectroscopic studies of Auger recombination in thick-shell ("giant") CdSe/CdS QDs with and without an interfacial alloy layer using time-tagged, time-correlated single-photon counting suggest that the positive trion is much shorter lived than the negative trion, which can be explained by a high density of valence band states and a small hole localization radius.
Abstract: Charged exciton states commonly occur both in spectroscopic studies of quantum dots (QDs) and during operation of QD-based devices. The extra charge added to the neutral exciton modifies its radiative decay rate and also opens an additional nonradiative pathway associated with an Auger process whereby the recombination energy of an exciton is transferred to the excess charge. Here we conduct single-dot spectroscopic studies of Auger recombination in thick-shell (“giant”) CdSe/CdS QDs with and without an interfacial alloy layer using time-tagged, time-correlated single-photon counting. In photoluminescence (PL) intensity trajectories of some of the dots, we resolve three distinct states of different emissivities (“bright”, “gray”, and “dark”) attributed, respectively, to the neutral exciton and negative and positive trions. Simultaneously acquired PL lifetime trajectories indicate that the positive trion is much shorter lived than the negative trion, which can be explained by a high density of valence band...
215 citations
TL;DR: In this article, the authors show that the photoluminescence (PL) quantum yield of as-processed MoS2 and WS2 monolayers reaches near-unity when they are made intrinsic through electrostatic doping, without any chemical passivation.
Abstract: Defects in conventional semiconductors substantially lower the photoluminescence (PL) quantum yield (QY), a key metric of optoelectronic performance that directly dictates the maximum device efficiency. Two-dimensional transition-metal dichalcogenides (TMDCs), such as monolayer MoS2, often exhibit low PL QY for as-processed samples, which has typically been attributed to a large native defect density. We show that the PL QY of as-processed MoS2 and WS2 monolayers reaches near-unity when they are made intrinsic through electrostatic doping, without any chemical passivation. Surprisingly, neutral exciton recombination is entirely radiative even in the presence of a high native defect density. This finding enables TMDC monolayers for optoelectronic device applications as the stringent requirement of low defect density is eased.
215 citations
TL;DR: For the first time, the nonresonant nonlinear susceptibility of semiconductors is derived from first principles including exciton correlations including excitation correlations.
Abstract: We consider a semiconductor of arbitrary dimension subject to a strong monochromatic laser beam in the transparency region below the exciton resonance. We calculate the spectrum of collective excitations and explain the recently observed dynamical Stark effect of the exciton. For the first time, we derive from first principles the nonresonant nonlinear susceptibility ${\ensuremath{\chi}}^{(3)}$ including exciton correlations.
215 citations