Emission Wavelength Of Quantum Dots Research Articles

Real-time monitoring of CdTe quantum dots growth in aqueous solution

Quantum dots (QDs) are remarkable semiconductor nanoparticles, whose optical properties are strongly size-dependent. Therefore, the real-time monitoring of crystal growth pathway during synthesis gives an excellent opportunity to a smart design of the QDs luminescence. In this work, we present a new approach for monitoring the formation of QDs in aqueous solution up to 90 °C, through in situ luminescence analysis, using CdTe as a model system. This technique allows a detailed examination of the evolution of their light emission. In contrast to in situ absorbance analysis, the in situ luminescence measurements in reflection geometry are particularly advantageous once they are not hindered by the concentration increase of the colloidal suspension. The synthesized particles were additionally characterized using X-ray diffraction analysis, transition electron microscopy, UV-Vis absorption and infrared spectroscopy. The infrared spectra showed that 3-mercaptopropionic acid (MPA)-based thiols are covalently bound on the surface of QDs and microscopy revealed the formation of CdS. Setting a total of 3 h of reaction time, for instance, the QDs synthesized at 70, 80 and 90 °C exhibit emission maxima centered at 550, 600 and 655 nm. The in situ monitoring approach opens doors for a more precise achievement of the desired emission wavelength of QDs.

High-directivity far-field radiation of quantum dot-based single-photon emitter coupled to polymeric circular waveguide resonant grating

Solid-state single-photon emitters (SPEs) commonly encounter the limitation of quasi-omnidirectional radiation patterns, which poses challenges in utilizing their emission with conventional optical instruments. In this study, we demonstrate the tailoring of the far-field radiation patterns of SPEs based on colloidal quantum dots (QDs), both theoretically and experimentally, by employing a polymer-based dielectric antenna. We introduce a simple and cost-effective technique, namely low one-photon absorption direct laser writing, to achieve precise coupling of a QD into an all-polymer circular waveguide resonance grating. By optimizing the geometry parameters of the structure using 3D finite-difference time-domain simulations, resonance at the emission wavelength of QDs is achieved in the direction perpendicular to the substrate, resulting in photon streams with remarkably high directivity on both sides of the grating. Theoretical calculations predict beam divergence values below 2°, while experimental measurements using back focal plane imaging yield divergence angles of approximately 8°. Our study contributes to the evaluation of concentric circular grating structures employing low refractive index polymer materials, thereby expanding the possibilities for their application.

Wafer-Scale Emission Energy Modulation of Indium Flushed Quantum Dots

Semiconductor self-assembled quantum dots (QDs) have garnered immense attention for their potential in various quantum technologies and photonics applications. Here, we explore a novel approach for fine-tuning the emission wavelength of QDs by building upon the indium flush growth method: Submonolayer variations in the capping thickness reveal a non-monotonic progression, where the emission energy can decrease even though the capping thickness decreases. indium flush, a well-known technique for inducing blue shifts in quantum dot emissions, involves the partial capping of QDs with GaAs followed by a temperature ramp-up. However, our findings reveal that the capping layer roughness, stemming from fractional monolayers during overgrowth, plays a pivotal role in modulating the emission energy of these QDs. We propose increased indium interdiffusion between the QDs and the surrounding GaAs capping layer for a rough surface surrounding the QD as the driving mechanism. This interdiffusion alters the indium content within the QDs, resulting in an additional emission energy shift, counterintuitive to the capping layer’s thickness increase. We utilize photoluminescence spectroscopy to generate wafer maps depicting the emission spectrum of the QDs. Using thickness gradients, we produce systematic variations in the capping layer thickness on 3″ wafers, resulting in modulations of the emission energy of up to 26 meV.

On-chip generation and dynamic piezo-optomechanical rotation of single photons

Integrated photonic circuits are key components for photonic quantum technologies and for the implementation of chip-based quantum devices. Future applications demand flexible architectures to overcome common limitations of many current devices, for instance the lack of tuneabilty or built-in quantum light sources. Here, we report on a dynamically reconfigurable integrated photonic circuit comprising integrated quantum dots (QDs), a Mach-Zehnder interferometer (MZI) and surface acoustic wave (SAW) transducers directly fabricated on a monolithic semiconductor platform. We demonstrate on-chip single photon generation by the QD and its sub-nanosecond dynamic on-chip control. Two independently applied SAWs piezo-optomechanically rotate the single photon in the MZI or spectrally modulate the QD emission wavelength. In the MZI, SAWs imprint a time-dependent optical phase and modulate the qubit rotation to the output superposition state. This enables dynamic single photon routing with frequencies exceeding one gigahertz. Finally, the combination of the dynamic single photon control and spectral tuning of the QD realizes wavelength multiplexing of the input photon state and demultiplexing it at the output. Our approach is scalable to multi-component integrated quantum photonic circuits and is compatible with hybrid photonic architectures and other key components for instance photonic resonators or on-chip detectors.

Metal–Organic Vapor‐Phase Epitaxy of Semipolar InGaN Quantum Dots Based on GaN V‐Shaped Pits

Semipolar {101} InGaN quantum dots (QDs) formed on GaN V‐shaped pits by metal–organic vapor‐phase epitaxy (MOVPE) with a growth interruption method are reported. The 3D GaN V‐pit structures are directly grown on a patterned sapphire substrate (PSS). By adjusting the pattern arrangement direction on the substrate, it is observed in the scanning electron microscopy (SEM) image that elliptical QDs are formed on the {101} semipolar sidewalls of the V‐pits with a density of about 5 × 1010 cm−2. The emission wavelength of semipolar InGaN QDs is confirmed by cathodoluminescence (CL). The gradient distribution of In composition and QD size are observed along the sidewall of the V‐pits. On this basis, a three‐period semipolar InGaN QD sample is prepared. For the temperature‐dependent photoluminescence (TDPL) test, the prominent peak of the sample shows a blueshift with the increase in temperature and reaches the green band (≈523 nm) at room temperature (RT). According to time‐resolved photoluminescence (TRPL) decay curves, a carrier lifetime of 329.3 ps fit by the stretched exponential model is obtained at RT. Compared with c‐plane QDs with the same growth method, the semipolar QDs have a shorter radiative recombination lifetime due to suppressed polarization electric field.

Thermodynamic properties in quantum dot nanocomposite for white light-emitted diodes

For a <span>colour conversion substance, we developed a new nanocomposite containing a CdSe/CdS/ZnS red-emitted quantum dot (QD), a green-emittedd <span>Sr<sub>2</sub>SiO<sub>4</sub>:Eu </span>phosphorus, and silicon resins. Regarding QD concentration and ingredients, the heat increase and optic features of the nanocomposite attributable to the QD inclusion were examined. According to the findings, a modest portion of QDs added to a photon converter at the emission wavelength of QD produced a considerable degree of heat. We used 0.2 wt% QDs over an InGaN blue-emitting light-emitted diodes (LED) chip to simulate a thermal increase in a nanocomposite. Consequently, we were able to produce a white-emitted LED module featuring a good 83.2 colour rendered index, an excellent 65.86 lm W-1 brightness, and a reasonable 94 °C thermal rise. The recently founded QD-phosphorus nanocomposite transformed white-emitted LED offers a lot of possibility of modern lighting.</span>

Self-assembled InAs/GaAs single quantum dots with suppressed InGaAs wetting layer states and low excitonic fine structure splitting for quantum memory

Abstract Epitaxial semiconductor quantum dots (QDs) have been demonstrated as on-demand entangled photon sources through biexciton–exciton (XX-X) cascaded radiative processes. However, perfect entangled photon emitters at the specific wavelengths of 880 nm or 980 nm, that are important for heralded entanglement distribution by absorptive quantum memories, remain a significant challenge. We successfully extend the QD emission wavelength to 880 nm via capping Stranski–Krastanow grown In(Ga)As/GaAs QDs with an ultra-thin Al x Ga1−x As layer. After carefully investigating the mechanisms governing the vanishing of wetting-layer (WL) states and the anisotropy of QDs, we optimize the growth conditions and achieve a strong suppression of the WL emission as well as a measured minor fine structure splitting of only ∼(3.2 ± 0.25) μeV for the exciton line. We further extend this method to fabricate In(Ga)As QDs emitted at 980 nm via introducing InGaAs capping layer, and demonstrate a two-photon resonant excitation of the biexciton without any additional optical or electrical stabilized source. These QDs with high symmetry and stability represent a highly promising platform for the generation of polarization entanglement and experiments on the interaction of photons from dissimilar sources, such as rare-earth-ion-doped crystals for solid quantum memory.

Improved Characteristics of CdSe/CdS/ZnS Core-Shell Quantum Dots Using an Oleylamine-Modified Process.

CdSe/CdS with ZnS/ZnO shell quantum dots (QDs) are synthesized by a one-pot method with various oleylamine (OLA) contents. The crystal structures of the QDs were analyzed by X-ray diffractometry, which showed ZnS diffraction peaks. It was represented that the ZnS shell was formed on the surface of the CdSe/CdS core. Interestingly, QDs with a high OLA concentration exhibit diffraction peaks of ZnS/ZnO. As a result, the thermal stability of QDs with ZnS/ZnO shells exhibits better performance than those with ZnS shells. In addition, the photoluminescence intensity of QDs with ZnS/ZnO shells shows a relatively slow decay of 7.1% compared with ZnS shells at 85 °C/85% relative humidity aging test for 500 h. These indicate that QDs with different OLA modifications can form ZnS/ZnO shells and have good stability in a harsh environment. The emission wavelength of QDs can be tuned from 505 to 610 nm, suitable for micro-LED display applications.

Broadband, efficient extraction of quantum light by a photonic device comprised of a metallic nano-ring and a gold back reflector

To implement quantum light sources based on quantum emitters in applications, it is desirable to improve the extraction efficiency of single photons. In particular, controlling the directionality and solid angle of the emission are key parameters, for instance, to couple single photons into optical fibers and send the information encoded in quantum light over long distances, for quantum communication applications. In addition, fundamental studies of the radiative behavior of quantum emitters, including studies of coherence and blinking, benefit from such improved photon collection. Quantum dots grown via Stranski–Krastanov technique have shown to be good candidates for bright, coherent, indistinguishable quantum light emission. However, one of the challenges associated with these quantum light sources arises from the fact that the emission wavelengths can vary from one emitter to the other. To this end, broadband light extractors that do not rely on high-quality factor optical cavities would be desirable, so that no tuning between the quantum dot emission wavelength and the resonator used to increase the light extraction is needed. Here, we show that metallic nano-rings combined with gold back reflectors increase the collection efficiency of single photons, and we study the statistics of this effect when quantum dots are spatially randomly distributed within the nano-rings. We show an average increase in the brightness of about a factor 7.5, when comparing emitters within and outside the nano-rings, in devices with a gold back reflector, and we measure count rates exceeding 7 × 106 photons per second and single photon purities as high as 85% ± 1%. These results are important steps toward the realization of scalable, broadband, easy to fabricate sources of quantum light for quantum communication applications.

Desorption induced formation of low-density GaN quantum dots: nanoscale correlation of structural and optical properties

We report on the formation process of GaN/AlN quantum dots (QDs) which arises after the deposition of 1–2 monolayers of GaN on an AlN/sapphire template followed by a distinct growth interruption (GRI). The influence of the duration of a GRI on the structural and optical properties of the GaN layer has been systematically investigated. QDs develop from initially bulky GaN islands, which nucleate in close vicinity to bundles of threading dislocations (TDs). For prolonged GRIs, a decreasing island size is observed which is consistent with a systematic blue shift of the emission wavelength. In addition, fragmentation of the bulky GaN islands into several smaller islands occurs, strongly dependent on local strain fields caused by TDs as well as on the different facet orientation of the islands. This morphological transition during GRI eventually leads to GaN QD formation, which assemble as clusters with a density of 108 cm−2. Desorption of GaN is identified as the major source for this morphological transition. The GRI time allows for tuning of the QD emission wavelength in the ultraviolet spectral range.

E‐Band InAs/GaAs Trilayer Quantum Dot Lasers

The introduction of a closely stacked quantum dot (QD) structure is considered as one of the most effective approaches to extend the emission wavelength of InAs/GaAs QDs beyond 1.3 μm (1300 nm). Herein, a trilayer QD structure (three closely stacked QD layers) is proposed to further extend the emission wavelength of QDs. Room‐temperature (RT) emission at 1418 nm from InAs/GaAs trilayer QDs is demonstrated. Moreover, based on these results, an E‐band InAs/GaAs trilayer QD laser is fabricated on a GaAs substrate, achieving RT oscillation at 1370 nm with a low threshold current density of 96 A cm−2 under continuous‐wave mode operation. The results indicate that the trilayer QD structure is promising for realizing high‐performance QD lasers on GaAs substrate over 1300 nm without incorporating metamorphic buffer layers.

Preparation and Research of Perovskite Quantum Dots Powder Based on RbCl Doped CsPbBr3

AbstractResearchers have achieved precise control of the size of quantum dots by using the quantum confinement effect. Rb+ and Cs+ with similar ionic radii have become a new mechanism for researchers to regulate the emission wavelength of quantum dots. However, there are few studies on the performance of codoped quantum dots with ion at present. By adding a saturated solution of RbCl into an organic solution of CsPbBr3, quantum dots doped with Rb+ and Cl− were prepared. The prepared quantum dots realized adjustable emission spectrum (457‐510 nm), stable lattice structure, and good stability under ultraviolet light irradiation. Therefore, double ion doping is a new method to prepare short‐wavelength of quantum dots.

Effect of Cap Thickness on InAs/InP Quantum Dots Grown by Droplet Epitaxy in Metal–Organic Vapor Phase Epitaxy

InAs quantum dots (QDs) are grown on bare InP(001) via droplet epitaxy (DE) in metal–organic vapor phase epitaxy (MOVPE). Capping layer engineering, used to control QD size and shape, is explored for DE QDs in MOVPE. The method allows for the tuning of the QD emission over a broad range of wavelengths, ranging from the O‐ to the L‐band. The effect of varying the InP capping layer is investigated optically by macro‐ and micro‐photoluminescence (PL, µPL) and morphologically by transmission electron microscopy (TEM). A strong 500 nm blueshift of the QD emission wavelength is observed when the capping layer is reduced from 20 to 8 nm, which is reflected by a clear size reduction of the buried QDs.

Spectral control of deterministically fabricated quantum dot waveguide systems using the quantum confined Stark effect

Quantum photonic circuits with integrated on-demand quantum emitters can act as building blocks for photonic gates and processors with enhanced quantum functionality. To scale up such quantum devices to larger and more powerful systems, eventually reaching the quantum advantage, the scalable integration of many emitters with identical emission wavelengths is of utmost importance. Here, we report on the deterministic integration of self-assembled quantum dots (QDs) in waveguide structures by means of in situ electron beam lithography (EBL). Applying external bias voltages to the p-i-n-doped and electrically contacted quantum circuits allows for spectral fine-tuning of the QDs via the quantum confined Stark effect. We achieve a tuning range of (0.40 ± 0.16) nm, which together with a spectral pre-selection accuracy of (0.2 ± 1.6) nm in the in situ EBL process is on average large enough to tune individual QDs into resonance. Thus, deterministic QD integration with spectral pre-selection in conjunction with Stark tuning of the QD emission wavelength is an attractive combination that has high potential to enable the scalable fabrication of integrated quantum photonic circuits in the future.

1.1 μm waveband tunable laser using emission-wavelength-controlled InAs quantum dots for swept-source optical coherence tomography applications

In this study, an optical gain chip using emission-wavelength-controlled self-assembled InAs quantum dots (QDs) was developed for swept-source optical coherence tomography (SS-OCT) applications. The optical characterizations indicated that the QDs emission wavelength and optical gain spectra were controlled in the 1.1μm waveband by optimizing the QDs growth conditions. This waveband is useful for obtaining a large imaging depth of OCT because of an optimal balance between absorption and scattering in biological samples. In addition, continuous tunable lasing in the waveband was achieved by introducing the QD-based gain chip into a grating-coupled external cavity. This tunable laser was introduced into an SS-OCT setup, and the point spread function (PSF) was evaluated. The PSF position was observed to vary according to the optical path length differences. These results demonstrate the feasibility of the application of emission-wavelength-controlled QDs for SS-OCT.

GaAsBi Quantum Dots for 1.55 μm Laser Diode

Bi incorporations can reduce the bandgap of GaAs1-xBix. With a Bi content of 10.5%, GaAsBi is predicted to emit light at 1.55 μm. However, high Bi incorporation is difficult for material growth and deteriorates the optical property of GaAsBi. In this work, a GaAsBi quantum dot (QD)/InAlAs structure on InP platform is proposed to fabricate 1.55 μm laser diodes. Strain distributions and band structures are calculated with different Bi contents and QD sizes using finite element method. High Bi contents and large QD sizes are beneficial for achieving long wavelengths. GaAsBi QD/InAlAs structures with a low Bi content of 5.6% and proper QD sizes, such as a diameter of 30 nm and a height of 6 nm, can emit light at 1.55 μm. The proposed structure can be realized by migration enhanced epitaxy and droplet epitaxy and provides a feasible way for fabricating GaAsBi based 1.55 μm laser diodes applied in fiber-optic communications. The emission wavelength of GaAsBi QDs with different sizes and Bi contents

Room-temperature ionic-liquid-assisted hydrothermal synthesis of Ag-In-Zn-S quantum dots for WLEDs

Synthesis of water-soluble I-III-VI type quantum dots (QDs) with high luminescence performance in efficient pathways still remains a tremendous challenge. In this study, water-soluble Ag-In-Zn-S (AIZS) QDs were prepared via the room temperature ionic liquids (RTILs) assisted hydrothermal method. The experimental results showed that the RTIL 1-methylimidazolium tetrafluoroborate ([Mim]BF4) played an important role in the phase structure, morphology, and optical properties of the AIZS QDs due to its high polarity and low surface tension, which was beneficial to the nucleation, growth, and surface modulation of QDs, resulting in the improvement of quantum yield (QY) from 23.2% to 28.9%. Moreover, the AIZS QDs exhibited long fluorescence lifetimes of 472.3 ns, further demonstrating the successful passivation of the trap states of QDs. Furthermore, the emission wavelength of AIZS QDs could be adjusted from 608 to 525 nm by tuning Ag/Zn ratios. Finally, a white light-emitting diode (WLED) based on AIZS QDs and green Lu3Al5O12:Ce3+ phosphor was successfully fabricated, which showed high luminous efficiency of 85.2 lm/W, color rendering index (CRI) of 62.2, and the correlated color temperature (CCT) of 6153 K, indicating the promising prospects of AIZS QDs’ application in photoelectric devices.

Effect of the Al content in the substrate on the In nanodroplets growth by droplet epitaxy

The paper presents the results of an experimental study of the effect of Al content in the epitaxial surface layer on the growth of In nanostructures formed by droplet epitaxy. We have shown that an increase in the Al content leads to a decrease in the droplet density and an increase in their size. We also showed that the influence of the Al content on the droplet characteristics is much less significant than that in case of the Stranski-Krastanov growth. The increase in the critical thickness of droplet formation on Al-containing surfaces when the temperature decreases is not significant. It allows us to control quantum dot emission wavelength almost independently of their geometric characteristics.

Self-assembled epitaxial metal–semiconductor nanostructures with enhanced GeSi quantum dot luminescence

Hybrid structures containing Ag nanoparticles and GeSi quantum dots were developed using the self-organization of metal nanoislands on the surface of a strained semiconductor structure. The enhanced photoluminescence from GeSi quantum dots (QDs) coupled with Ag nanoislands was obtained. Ag nanoislands epitaxially grown on top of the multilayered structures with GeSi QDs support a surface plasmon resonance that can be tuned to the QD emission wavelength by changing Ag nanoparticle parameters. The numerical modeling of surface plasmon resonance allows attributing this effect to the increase of the recombination rate due to the coupling of QD emitters with Ag nanoislands.

InAs/InP quantum dot VECSEL emitting at 1.5 μm

A high-power InAs quantum dot (QD) vertical-external-cavity surface-emitting laser emitting at 1.5 μm is reported. The active region employs 20 layers of high-density Stranski–Krastanow InAs quantum dots on an InP substrate. The QD density and emission wavelength were independently adjusted by employing a double-cap growth sequence. Optimization of the spacer layer thickness and strain compensation rendered possible nucleation of a relatively high number of QD layers per antinode of the electromagnetic standing wave, which in turn enabled a high output power continuous wave operation of about 2.2 W. The operation wavelength could be tuned over 60 nm, taking advantage of the broadband gain characteristic of QD media.