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9 pages, 3991 KiB

Open AccessArticle

Investigation on the Optical Properties of Micro-LEDs Based on InGaN Quantum Dots Grown by Molecular Beam Epitaxy

by Ying Gu, Yi Gong, Peng Zhang, Haowen Hua, Shan Jin, Wenxian Yang, Jianjun Zhu and Shulong Lu

Nanomaterials 2023, 13(8), 1346; https://0-doi-org.brum.beds.ac.uk/10.3390/nano13081346 - 12 Apr 2023

Cited by 1 | Viewed by 1508

Abstract

InGaN quantum dots (QDs) have attracted significant attention as a promising material for high-efficiency micro-LEDs. In this study, plasma-assisted molecular beam epitaxy (PA-MBE) was used to grow self-assembled InGaN QDs for the fabrication of green micro-LEDs. The InGaN QDs exhibited a high density [...] Read more.

InGaN quantum dots (QDs) have attracted significant attention as a promising material for high-efficiency micro-LEDs. In this study, plasma-assisted molecular beam epitaxy (PA-MBE) was used to grow self-assembled InGaN QDs for the fabrication of green micro-LEDs. The InGaN QDs exhibited a high density of over 3.0 × 10¹⁰ cm⁻², along with good dispersion and uniform size distribution. Micro-LEDs based on QDs with side lengths of the square mesa of 4, 8, 10, and 20 μm were prepared. Attributed to the shielding effect of QDs on the polarized field, luminescence tests indicated that InGaN QDs micro-LEDs exhibited excellent wavelength stability with increasing injection current density. The micro-LEDs with a side length of 8 μm showed a shift of 16.9 nm in the peak of emission wavelength as the injection current increased from 1 A/cm² to 1000 A/cm². Furthermore, InGaN QDs micro-LEDs maintained good performance stability with decreasing platform size at low current density. The EQE peak of the 8 μm micro-LEDs is 0.42%, which is 91% of the EQE peak of the 20 µm devices. This phenomenon can be attributed to the confinement effect of QDs on carriers, which is significant for the development of full-color micro-LED displays. Full article

(This article belongs to the Special Issue Quantum Dots)

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14 pages, 1703 KiB

Open AccessArticle

A Comparative Study of the Band-Edge Exciton Fine Structure in Zinc Blende and Wurtzite CdSe Nanocrystals

by Aleksandr A. Golovatenko, Ina V. Kalitukha, Grigorii S. Dimitriev, Victor F. Sapega, Maxim V. Rakhlin, Aidar I. Galimov, Tatiana V. Shubina, Elena V. Shornikova, Gang Qiang, Dmitri R. Yakovlev, Manfred Bayer, Amelie Biermann, Axel Hoffmann, Tangi Aubert, Zeger Hens and Anna V. Rodina

Nanomaterials 2022, 12(23), 4269; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12234269 - 01 Dec 2022

Cited by 2 | Viewed by 1831

Abstract

In this paper, we studied the role of the crystal structure in spheroidal CdSe nanocrystals on the band-edge exciton fine structure. Ensembles of zinc blende and wurtzite CdSe nanocrystals are investigated experimentally by two optical techniques: fluorescence line narrowing (FLN) and time-resolved photoluminescence. [...] Read more.

In this paper, we studied the role of the crystal structure in spheroidal CdSe nanocrystals on the band-edge exciton fine structure. Ensembles of zinc blende and wurtzite CdSe nanocrystals are investigated experimentally by two optical techniques: fluorescence line narrowing (FLN) and time-resolved photoluminescence. We argue that the zero-phonon line evaluated by the FLN technique gives the ensemble-averaged energy splitting between the lowest bright and dark exciton states, while the activation energy from the temperature-dependent photoluminescence decay is smaller and corresponds to the energy of an acoustic phonon. The energy splittings between the bright and dark exciton states determined using the FLN technique are found to be the same for zinc blende and wurtzite CdSe nanocrystals. Within the effective mass approximation, we develop a theoretical model considering the following factors: (i) influence of the nanocrystal shape on the bright–dark exciton splitting and the oscillator strength of the bright exciton, and (ii) shape dispersion in the ensemble of the nanocrystals. We show that these two factors result in similar calculated zero-phonon lines in zinc blende and wurtzite CdSe nanocrystals. The account of the nanocrystals shape dispersion allows us to evaluate the linewidth of the zero-phonon line. Full article

(This article belongs to the Special Issue Quantum Dots)

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11 pages, 700 KiB

Open AccessArticle

Effects of Applied Magnetic Field on the Optical Properties and Binding Energies Spherical GaAs Quantum Dot with Donor Impurity

by Collins Okon Edet, Emre Bahadir Al, Fatih Ungan, Norshamsuri Ali, Nursalasawati Rusli, Syed Alwee Aljunid, Rosdisham Endut and Muhammad Asjad

Nanomaterials 2022, 12(16), 2741; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12162741 - 10 Aug 2022

Cited by 11 | Viewed by 1456

Abstract

The screened modified Kratzer potential (SMKP) model is utilized to scrutinize the impacts of an applied magnetic field (MF) on the binding energies and linear and nonlinear optical properties spherical GaAs quantum dot with donor impurity (DI). To accomplish this goal, we have [...] Read more.

The screened modified Kratzer potential (SMKP) model is utilized to scrutinize the impacts of an applied magnetic field (MF) on the binding energies and linear and nonlinear optical properties spherical GaAs quantum dot with donor impurity (DI). To accomplish this goal, we have used the diagonalization method to numerically solve the Schrödinger equation under the effective mass approximation for obtaining the electron energy levels and related electronic wave functions. The expressions used for evaluating linear, third-order nonlinear, and total optical absorption coefficients and relative refractive index changes were previously derived within the compact density matrix method. It has been shown here that the MF and DI impacts the characteristics of the absorption coefficients and the refractive index changes. This study’s results will find application in optoelectronics and related areas. Full article

(This article belongs to the Special Issue Quantum Dots)

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11 pages, 2841 KiB

Open AccessFeature PaperArticle

Experimentally-Verified Modeling of InGaAs Quantum Dots

by Alexander N. Kosarev, Vladimir V. Chaldyshev and Nikolay Cherkashin

Nanomaterials 2022, 12(12), 1967; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12121967 - 08 Jun 2022

Cited by 4 | Viewed by 1561

Abstract

We develop a model of an epitaxial self-organized InGaAs quantum dot buried in GaAs, which takes into account experimentally determined indium distribution inside the QD, its geometry and crystallography. The problem of solid mechanics was solved to determine the stress-strain field. Then, the [...] Read more.

We develop a model of an epitaxial self-organized InGaAs quantum dot buried in GaAs, which takes into account experimentally determined indium distribution inside the QD, its geometry and crystallography. The problem of solid mechanics was solved to determine the stress-strain field. Then, the parameters of the electron and hole ground states were evaluated by solving the problem of the quantum mechanics on the same mesh. The results of calculations appeared to be reasonably well consistent with experimentally recorded optical emission spectra for the QDs in the same sample. The experimentally-verified modeling reveals a bagel-like shape of the hole wave function at the ground state, which should considerably impact the optical and magnetic properties of the QDs. Such shape of the wave function is beyond the predictions of simplified models with uniform indium distribution. Full article

(This article belongs to the Special Issue Quantum Dots)

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8 pages, 554 KiB

Open AccessArticle

Bright Single-Photon Sources for the Telecommunication O-Band Based on an InAs Quantum Dot with (In)GaAs Asymmetric Barriers in a Photonic Nanoantenna

by Maxim Rakhlin, Grigorii Klimko, Sergey Sorokin, Marina Kulagina, Yurii Zadiranov, Dmitrii Kazanov, Tatiana Shubina, Sergey Ivanov and Alexey Toropov

Nanomaterials 2022, 12(9), 1562; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12091562 - 05 May 2022

Cited by 2 | Viewed by 1869

Abstract

We report on single-photon emitters for the telecommunication O-band (1260–1360 nm), which comprise an InAs/(In)GaAs quantum dot with asymmetric barriers, placed inside a semiconductor tapered nanocolumn acting as a photonic nanoantenna. The implemented design of the barriers provides a shift in the quantum [...] Read more.

We report on single-photon emitters for the telecommunication O-band (1260–1360 nm), which comprise an InAs/(In)GaAs quantum dot with asymmetric barriers, placed inside a semiconductor tapered nanocolumn acting as a photonic nanoantenna. The implemented design of the barriers provides a shift in the quantum dot radiation wavelength towards the O-band, while the nanoantenna collects the radiation and ensures its effective output. With non-resonant optical pumping, the average count rate of emitted single photons exceeds 10 MHz with the second-order correlation function

g^{(2)}

(0) = 0.18 at 8 K. Full article

(This article belongs to the Special Issue Quantum Dots)

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22 pages, 4921 KiB

Open AccessEditor’s ChoiceArticle

Majorana Anyon Composites in Magneto-Photoluminescence Spectra of Natural Quantum Hall Puddles

by Alexander M. Mintairov, Dmitrii V. Lebedev, Alexey S. Vlasov and Steven A. Blundell

Nanomaterials 2022, 12(6), 1016; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12061016 - 20 Mar 2022

Cited by 2 | Viewed by 1899

Abstract

In magneto-photoluminescence (magneto-PL) spectra of quasi two-dimensional islands (quantum dots) having seven electrons and Wigner–Seitz radius r_s~1.5, we revealed a suppression of magnetic field (B) dispersion, paramagnetic shifts, and jumps of the energy of the emission components for filling [...] Read more.

In magneto-photoluminescence (magneto-PL) spectra of quasi two-dimensional islands (quantum dots) having seven electrons and Wigner–Seitz radius r_s~1.5, we revealed a suppression of magnetic field (B) dispersion, paramagnetic shifts, and jumps of the energy of the emission components for filling factors ν > 1 (B < 10 T). Additionally, we observed B-hysteresis of the jumps and a dependence of all these anomalous features on r_s. Using a theoretical description of the magneto-PL spectra and an analysis of the electronic structure of these dots based on the single-particle Fock–Darwin spectrum and many-particle configuration-interaction calculations, we show that these observations can be described by the r_s-dependent formation of the anyon (magneto-electron) composites (ACs) involving single-particle states having non-zero angular momentum and that the anyon states observed involve Majorana modes (MMs), including zero-B modes having an equal number of vortexes and anti-vortexes, which can be considered as Majorana anyons. We show that the paramagnetic shift corresponds to a destruction of the equilibrium self-formed ν~5/2 AC by the external magnetic field and that the jumps and their hysteresis can be described in terms of Majorana qubit states controlled by B and r_s. Our results show a critical role of quantum confinement in the formation of magneto-electrons and implies the liquid-crystal nature of fractional quantum Hall effect states, the Majorana anyon origin of the states having even ν, i.e., composite fermions, which provide new opportunities for topological quantum computing. Full article

(This article belongs to the Special Issue Quantum Dots)

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13 pages, 4532 KiB

Open AccessFeature PaperArticle

Optical and Physicochemical Characterizations of a Cellulosic/CdSe-QDs@S-DAB₅ Film

by Manuel Algarra, Ana L. Cuevas, Ma Valle Martínez de Yuso, Rocío Romero, Beatriz Alonso, Carmen M. Casado and Juana Benavente

Nanomaterials 2022, 12(3), 484; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12030484 - 29 Jan 2022

Cited by 4 | Viewed by 1947

Abstract

CdSe quantum dots nanoparticles were coated with the thiolated (DiAminoButane based dendrimer) DAB dendrimer of fifth generation (S-DAB₅) and embedded in a highly hydrophilic regenerated cellulose (RC) film by simple dip-coating method (immersion in QD-dendrimer aqueous solution) as a way to [...] Read more.

CdSe quantum dots nanoparticles were coated with the thiolated (DiAminoButane based dendrimer) DAB dendrimer of fifth generation (S-DAB₅) and embedded in a highly hydrophilic regenerated cellulose (RC) film by simple dip-coating method (immersion in QD-dendrimer aqueous solution) as a way to get a flexible nano-engineered film (RC-4/CdSe-QDs@S-DAB₅) with high transparency and photoluminescence properties for different applications. Optical changes in the RC film associated with QDs inclusion were determined by spectroscopic ellipsometry (SE) measurements, which provide information on changes caused in the refraction index and the extinction coefficients of the film, as well as by light transmittance/reflectance curves and photoluminescence (PL) spectra. Impedance spectroscopy (IS) and other typical physicochemical techniques for material characterization (TEM, SEM and XPS) have also been used in order to have more complete information on film characteristics. A comparison of RC-4/CdSe-QDs@S-DAB₅ film optical characteristics with those exhibited by other RC-modified films depending on the type of dendrimer was also carried out. Full article

(This article belongs to the Special Issue Quantum Dots)

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Review

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23 pages, 5501 KiB

Open AccessReview

Exfoliation of MoS₂ Quantum Dots: Recent Progress and Challenges

by Luqman Ali, Fazle Subhan, Muhammad Ayaz, Syed Shams ul Hassan, Clare Chisu Byeon, Jong Su Kim and Simona Bungau

Nanomaterials 2022, 12(19), 3465; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12193465 - 04 Oct 2022

Cited by 12 | Viewed by 2564

Abstract

Although, quantum dots (QDs) of two-dimensional (2D) molybdenum disulfide (MoS₂) have shown great potential for various applications, such as sensing, catalysis, energy storage, and electronics. However, the lack of a simple, scalable, and inexpensive fabrication method for QDs is still a [...] Read more.

Although, quantum dots (QDs) of two-dimensional (2D) molybdenum disulfide (MoS₂) have shown great potential for various applications, such as sensing, catalysis, energy storage, and electronics. However, the lack of a simple, scalable, and inexpensive fabrication method for QDs is still a challenge. To overcome this challenge, a lot of attention has been given to the fabrication of QDs, and several fabrication strategies have been established. These exfoliation processes are mainly divided into two categories, the ‘top-down’ and ‘bottom-up’ methods. In this review, we have discussed different top-down exfoliation methods used for the fabrication of MoS₂ QDs and the advantages and limitations of these methods. A detailed description of the various properties of QDs is also presented. Full article

(This article belongs to the Special Issue Quantum Dots)

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