E. Marega

Exciton localization and temperature stability in self‐organized InAs quantum dots

We investigated the temperature effect on exciton localization in self‐organized InAs quantum dots. Quenching energy for excitons in reference quantum well and quantum dots was found to be 2 and 7 meV, respectively. Thermoactivation energy of electron‐hole emission through a GaAs barrier in the quantum dots was measured as 46 meV. We observed an unusual decrease of photoluminescence peak full width at half maximum with temperature, suggesting suppression of nonpredominant size quantum dot emissions due to carrier tunneling between nearby dots.

High index orientation effects of strained self‐assembled InGaAs quantum dots

Optical characterization of strained InGaAs/GaAs quantum dots grown by molecular beam epitaxy on (001) and (n11)B, where n=1, 2, 3, 5, and 7 orientations is reported in this work. Quantum dot photoluminescence emission shows remarkable orientation effects, presented in peak shape, full width at half‐maximum, and integrated intensity. Quantum dots grown on the (711)B plane demonstrate high quantum efficiency: integrated photoluminescence ratio between quantum dots and quantum well is about 10. Our results indicate an enhancement of the quantum dots onset thermal quenching energy by a factor of 2.5 for all orientations. Activation energy for thermal stimulated electron–hole emission in quantum dots is 2–5 times higher than in quantum wells. Photoluminescence polarization measurements show strong in‐plane dependence caused by the quantum dots’ structural anisotropy.

Localized surface plasmon resonance interaction with Er3+-doped tellurite glass

We show the annealing effect on silver and Erbium-doped tellurite glasses in the formation of nanoparticles (NPs) of silver, produced by the reduction of silver (Ag+ → Ag0), aiming to an fluorescence enhancement. The absorption spectra show typical Localized Surface Plasmon Resonance (LSPR) band of Ag0 NP in addition to the distinctive absorption peaks of Er3+ ions. Both observations demonstrate that the photoluminescence enhancement is due to the coupling of dipoles formed by NPs with the Er3+ 4I(13/2) → 4I(15/2) transition. This plasmon energy transfer to the Er3+ ions was observed in the fluorescence spectrum with a blue-shift of the peaks.

Aharonov-Bohm interference in neutral excitons: effects of built-in electric fields

We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.

Directed self-assembly of quantum structures by nanomechanical stamping using probe tips

We demonstrate that nanomechanically stamped substrates can be used as templates to pattern and direct the self-assembly of epitaxial quantum structures such as quantum dots. Diamond probe tips are used to indent or stamp the surface of GaAs(100) to create nanoscale volumes of dislocation-mediated deformation, which alter the growth surface strain. These strained sites act to bias nucleation, hence allowing for selective growth of InAs quantum dots. Patterns of quantum dots are observed to form above the underlying nanostamped template. The strain state of the patterned structures is characterized by micro-Raman spectroscopy. The potential of using nanoprobe tips as a quantum dot nanofabrication technology are discussed.

Spin splitting of the electron ground states of InAs quantum dots

Here, we present results on the spin splitting of electrons in the ground state of InAs self-assembled quantum dots (QDs). The spin splitting is assessed by capacitance spectroscopy, which allows direct measurement of the electronic g-factor modulus. By applying the magnetic field parallel to the [001], [110], and [110] crystallographic directions, we found that for magnetic fields below 5 T the g factor depends on the orientation, reflecting the QD anisotropy. For higher fields, the g factor does not exhibit the same degree of anisotropy, indicating a compression of the wave function inside the QD along the [001] direction, and consequently, a dependence on the magnitude of the applied field.

Laterally aligned quantum rings: From one-dimensional chains to two-dimensional arrays

We present the fabrication of ordered quantum rings by the conversion of partially capped quantum dots. Morphological transformation of quantum dots to quantum rings is demonstrated by partially capping self-assembled quantum dots. Quantum rings have been fabricated on high index surfaces by this growth technique. The lateral ordering of quantum rings is introduced by engineering the strain field of a multi-layer InGaAs superlattice template. By using high index surfaces, the one-dimensional ordering of quantum rings on GaAs (100) surface was observed to evolve into two-dimensional aligned quantum ring arrays.

Study of Er3+ fluorescence on tellurite glasses containing Ag nanoparticles

Optical characteristics of tellurite glasses containing silver nanoparticles (NPs) and the influence on the emission spectrum of Er3+ ions were studied. The transitions 4f 4f from erbium ions, mainly the 4I13/2 → 4I15/2 transition that involve upconversion energy process, have a strongly dependence with the chemical structure of the rare earth ion. In the present work, silver nanparticles (NPs) embedded in the host vitreous material, show a significant enhance (or quenching) on the erbium fluorescence due the long-range electromagnetic interaction between the plasmon surface energy of the Ag NPs (Localized Surface Plasmon Resonance -LSPR) and the Er3+ ions.

Tunneling-barrier controlled excitation transfer in hybrid quantum dot-quantum well nanostructures

A systematic spectroscopic study of the carrier transfer between quantum dot (QD) and quantum well (QW) layers is carried out in a hybrid dot-well system based on InAs QDs and InGaAs QWs. We observe a strong dependence of the QD and QW photoluminescence (PL) both on the dot-well barrier thickness and height. For thick (or high) barriers QD and QW systems accumulate independently sufficient photogenerated carrier densities to be seen in PL even at low nonresonant excitation power. For thin (or low) barriers it is impossible to detect the PL signal from QW at low excitation densities due to effective carrier transfer from QW to QDs. Strong state-filling effects of the excited QD states influence the carrier transfer efficiencies. By investigating the carrier dynamics using time-resolved spectroscopy and the state-filling effects in the continuous wave excitation regime the basic characteristics of interlevel, intersublevel, and dot-well relaxation are determined. The mechanisms of the dot-well coupling are ...

Self-organized InGaAs quantum dots grown by molecular beam epitaxy on (100), (711)AB, (511)AB, (311)AB, (211)AB, and (111)AB oriented GaAs

In this paper, we report optical properties of InGaAs quantum dots grown by molecular beam epitaxy on GaAs (n11)AB, where n is 1, 2, 3, 5 and 7, and reference (100) substrates. A higher crystal quality of quantum dots has been detected on (n11)B surfaces due to the strong integrated photoluminescence (PL) intensity, its value on (711)B orientation being 10 times larger than the QW one. Quantum dots grown on a (311)B surface showed a higher homogeneity in size. The quantum well PL peak position reveals a non-monotonical red-shift when the surface direction changes from (100) to (111).