Continuum and discrete excitation spectrum of single quantum rings

Alén, Benito; Martínez‐Pastor, Juan P.; Granados, Daniel; García, J. M.

doi:10.1103/physrevb.72.155331

Cited by 49 publications

(46 citation statements)

References 42 publications

(59 reference statements)

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“…The approximately constant excited state splitting found indicates that the QD lateral confinement could be described by a smooth parabolic potential. 18 The average value of ⌬E ϳ 38 meV is smaller by 30%-50% than those reported in the literature for QDs emitting below 1.2 eV, 15,16 and it suggests, within this model, that type-A QDs exhibit a larger diameter than standing InAs/ GaAs self-assembled QDs with similar ground state energy. Finally, for the type-B QD ensemble, we have found only one excited state ͑B 1 ͒ splitted by 34.9 meV from its fundamental state in good correspondence with values reported in the literature for QDs emitting above 1.3 eV.…”

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confidence: 43%

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Formation and optical characterization of single InAs quantum dots grown on GaAs nanoholes

Alonso‐González¹,

Alén²,

Fuster³

et al. 2007

Applied Physics Letters

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We present a study of the structural and optical properties of InAs quantum dots formed in a low density template of nanoholes fabricated by droplet epitaxy on GaAs ͑001͒. The growth conditions used here promote the formation of isolated quantum dots only inside the templated nanoholes. Due to the good optical quality and low density of these nanostructures, their ensemble and individual emission properties could be investigated and related to the particular growth method employed and the quantum dot morphology. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2799736͔ New nanoelectronics and quantum information perspectives require the ability of growing nanostructures with control in size and spatial location. In particular, for the application of quantum devices based in single quantum dots 1,2 ͑QDs͒ as, for instance, single photon emitters, it is necessary to combine strategies that would permit precise location of a single nanostructure presenting at the same time high optical quality. [3][4][5][6] With this aim, a quite wide-spread strategy to overcome the randomly positioning of self-assembled nanostructures is based on the use of patterned substrates to create preferential nucleation sites that define the position and size of the nanostructures. In particular, highly ordered arrays of QDs have been already obtained using different lithographic approaches followed by an appropriate regrowth process. 5,7,8 In this situation, the droplet epitaxy has revealed itself as a potential technique to achieve templates for localization of nanostructures with high optical quality in latticemismatched heteroepitaxial systems. 9 This technique has been mainly developed in GaAs based systems and basically consists of the supply of a certain amount of Ga during growth to form metallic droplets on the surface, which are later transformed into crystalline GaAs under arsenic atmosphere. Under certain experimental conditions, the crystallization process leads to the formation of specific structures containing nanoholes that act as preferential sites for InAs QD nucleation upon further InAs deposition. 10 The density of nanoholes corresponds to that of the droplets, being possible to obtain QD densities as low as 10 7 cm −2 . 11 The size of these nanostructures is related to the amount of InAs filling the nanoholes, with independence of their density, as opposed to the QD formation by self-assembling processes. This fact is especially interesting for applications based on a single QD. Furthermore, in coincidence with other lithographic techniques, 12 a different number of QD per nanohole can also be obtained. 13 In this situation, one advantage of the droplet epitaxy technique is that it can provide nanotemplates for QD formation without the need of growing thick buffer layers to avoid the influence of residual contamination from the fabrication process on the optical properties of the nanostructures.This work deals with the structural and optical characterization of InAs QDs formed in a template of 2.4 ϫ 10 8 cm −2 nano...

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confidence: 43%

“…The relative splittings found among the different -PL lines are characteristic of negatively charged exciton recombination in QDs of this size. 18 Yet, this assignment can be further confirmed by measuring the polarization resolved spectrum for each line, as shown in Fig. 3͑b͒.…”

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confidence: 95%

Formation and optical characterization of single InAs quantum dots grown on GaAs nanoholes

Alonso‐González¹,

Alén²,

Fuster³

et al. 2007

Applied Physics Letters

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“…These values of K are of the same order than the inverse of the exciton localization length, 1=L X $ 0:2 nm À1 , with L X $ 5 nm typical for small QDs. 46 …”

Section: A Thermal Escapementioning

confidence: 99%

Size dependent carrier thermal escape and transfer in bimodally distributed self assembled InAs/GaAs quantum dots

Muñoz‐Matutano

Suárez²,

Canet‐Ferrer

et al. 2012

Journal of Applied Physics

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We have investigated the temperature dependent recombination dynamics in two bimodally distributed InAs self assembled quantum dots samples. A rate equations model has been implemented to investigate the thermally activated carrier escape mechanism which changes from exciton-like to uncorrelated electron and hole pairs as the quantum dot size varies. For the smaller dots, we find a hot exciton thermal escape process. We evaluated the thermal transfer process between quantum dots by the quantum dot density and carrier escape properties of both samples.

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“…The tunneling rates are determined by the carrier confinement energies and therefore depend on the QD size and the Coulomb interactions between electrons and holes. 22,26 This leads to µ-PL contour maps with characteristic staircase patterns and energy splittings which are different for single QDs and QD pairs.…”

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confidence: 99%

“…The latter causes the switching of spectral lines which we associate with the recombination of exciton complexes with a varying number of electrons. 22 If the crystallization of the Ga droplet is not complete, arsenic vacancies arise during growth, creating localized states in the gap. These localized states are close in energy to the electron confined levels and are occupied by one or more electrons depending on their state of valence.…”

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Charge control in laterally coupled double quantum dots

et al. 2011

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We investigate the electronic and optical properties of InAs double quantum dots grown on GaAs (001) and laterally aligned along the [110] crystal direction. The emission spectrum has been investigated as a function of a lateral electric field applied along the quantum dot pair mutual axis. The number of confined electrons can be controlled with the external bias, leading to sharp energy shifts which we use to identify the emission from neutral and charged exciton complexes. Quantum tunneling of these electrons is proposed to explain the reversed ordering of the trion emission lines as compared to that of excitons in our system. Optical spin initialization of individual electrons is a fundamental resource for quantum information science which relies on our ability to control the charge in a quantum dot (QD) molecule. [1][2][3] In the past, vertically aligned QDs have been fabricated with great success. In these systems, exciton coupling signatures including energy anticrossings of neutral and charged exciton complexes, have been demonstrated by applying an electric field in the growth direction.4-6 Lateral QD molecules would be a better candidate for scaling up the electronic coupling from two to several QDs by applying individual lateral gates. Previous demonstrations of electronic coupling in a lateral QD pair have been based on an analysis of the anomalous Stark shifts and photon correlation statistics of the neutral exciton under a lateral electric field.7 Yet, the observation of electrically tunable energy anticrossings in lateral QD molecules remains a difficult task due to the exponential decrease of the tunnel coupling energy with the center-to-center QD distance d. [7][8][9] In the following, we investigate the emission spectrum of electrically tunable lateral QD pairs with a varying number of electrons. For typical interdot distances d ∼ 30-40 nm, we find that electron tunneling phenomena affect the negative trion emission energy before clear exciton anticrossings may take place.For the present study, QD pairs aligned in the [110] crystal direction were fabricated on GaAs nanoholes using a modified droplet epitaxy growth procedure as described in detail elsewhere. 10 The nanostructures were grown on a 0.5-µm-thick undoped GaAs buffer layer and capped by 100 nm of undoped GaAs. Atomic force micrographs (AFMs) performed on a similar uncapped sample revealed that each QD in the pair has a slightly different height, with average values of 5.3 ± 0.9 and 6.6 ± 1.5 nm, respectively, and centerto-center separation equal to their average diameter 37 ± 4 nm [ Fig. 1(a)]. The morphological analysis also revealed that QD pair formation occurs in 95% of the cases with a small probability for single QDs or empty nanoholes. The low areal density of 2 × 10 8 cm −2 is adequate to study individual quantum nanostructures.To apply an electric field along the QD pair mutual axis, we defined metal-semiconductor-metal (MSM) diodes by evaporation of two metal contacts (15 nm Mo + 30 nm Au) on top of 100-µm-square mesas. The ...

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Continuum and discrete excitation spectrum of single quantum rings

Cited by 49 publications

References 42 publications

Formation and optical characterization of single InAs quantum dots grown on GaAs nanoholes

Formation and optical characterization of single InAs quantum dots grown on GaAs nanoholes

Size dependent carrier thermal escape and transfer in bimodally distributed self assembled InAs/GaAs quantum dots

Charge control in laterally coupled double quantum dots

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