Quantum Dot Energy Research Articles

Josephson current across a Double Quantum Dot Josephson junction in T-Shape Configuration

By implementing the Keldysh non-equilibrium Green's function equation of motion approach, Josephson current has been examined across a T-shaped uncorrelated double quantum dot Josephson junction. The behavior of the Josephson current as a function of the main quantum dot energy level for varied interdot tunneling and different dot-lead coupling strengths is examined. With this configuration, we illustrate that the side-attached quantum dot offers an alternative route for electron transmission, which modifies the Josephson current by varying interdot tunneling. Further, we also investigate how the dot-lead coupling strengths affect the Josephson current.

Magnetic field effect on transport properties of double quantum dot — Majorana wire system in cross-shaped configuration

We theoretically study the influence of an external magnetic field on the transport properties of a double quantum dot (DQD)-Majorana nanowire system in a cross-shaped configuration with central dot coupled to a superconductor and normal metallic leads. In such a system, we can observe a subtle interplay between generation of Andreev bound states, Majorana mode leaking into quantum dots and interdots Fano-like interference processes. We show that properly selected side-coupled quantum dot energy can slow down/activate the process of Majorana mode leaking into DQD and additionally can strongly affect the differential and linear conductance in the considered system. We also study the influence of spin polarization of quantum dot–Majorana mode coupling on the transport properties of the considered system, especially on its linear conductance.

Single PbS colloidal quantum dot transistors

Colloidal quantum dots are sub-10 nm semiconductors treated with liquid processes, rendering them attractive candidates for single-electron transistors operating at high temperatures. However, there have been few reports on single-electron transistors using colloidal quantum dots due to the difficulty in fabrication. In this work, we fabricated single-electron transistors using single oleic acid-capped PbS quantum dot coupled to nanogap metal electrodes and measured single-electron tunneling. We observed dot size-dependent carrier transport, orbital-dependent electron charging energy and conductance, electric field modulation of the electron confinement potential, and the Kondo effect, which provide nanoscopic insights into carrier transport through single colloidal quantum dots. Moreover, the large charging energy in small quantum dots enables single-electron transistor operation even at room temperature. These findings, as well as the commercial availability and high stability, make PbS quantum dots promising for the development of quantum information and optoelectronic devices, particularly room-temperature single-electron transistors with excellent optical properties.

Simulation study on quantum dot formation of double-qubit-Si-MOS device

Silicon quantum dots (QDs) are essential physical carriers of quantum bits (qubits) in quantum computing. However, their extremely small size renders them highly sensitive to both the fabrication process and surrounding environment. Accuracy and stability must be carefully considered. In this study, we propose a double gate QD device model based on silicon metal-oxide-semiconductor (Si-MOS) for the generation of spin qubits. Using a Technology Computer Aided Design (TCAD) simulation, we investigated the impact of device dimensions, including oxide layer thickness, channel length, and spacer length, on the QD structure. Additionally, we examined the effects of the temperature and interface trap concentration on QD formation. An equivalent circuit model was employed to assess the charging energy (Ec) of QDs. Our results demonstrate that by appropriately adjusting these parameters, it is possible to achieve a QD structure with a wide level spacing and small size capable of accommodating as few as four electrons. Furthermore, we calculated an Ec of 33 meV for the QDs.

Post‐Passivation of Perovskite Quantum Dots by Conjugated Molecules for Spectrally Stable and Efficient Deep Blue Light‐Emitting Diodes

AbstractPerovskite light‐emitting diodes (PeLEDs) are promising candidates for displays and solid‐state lighting due to their tunable colors, high conversion efficiency, and low cost. However, the performance of deep blue PeLEDs lags far behind that of near‐infrared, red, and green ones. Here, the ligand concentration on the perovskite surface is regulated by introducing a small organic molecule 3‐(5,9‐dioxa‐13b‐boranaphtho [3,2,1‐d,e] anthracene‐7‐yl)‐9‐phenyl‐9H‐carbazole (BOCzPh) to reduce the defects in the mixed‐halogen perovskite lattice and improve the exciton binding energy of perovskite quantum dots (QDs). Finally, deep blue PeLEDs with an emission peak at 469 nm, a peak external quantum efficiency of 2.8%, and a maximum brightness of 851 cd m−2 are obtained. Owing to the post‐passivation of QDs by BOCzPh molecules, the emission spectra of the mixed‐halide perovskites are stabilized and the luminous efficiency of the devices is improved simultaneously. This work provides a new approach to realize spectrally stable and efficient deep blue PeLEDs.

Hydrogenic donor-related binding energy and diamagnetic susceptibility in multilayer cylindrical quantum dots under hydrostatic pressure

Hydrogenic donor-related binding energy and diamagnetic susceptibility in multilayer cylindrical quantum dots under hydrostatic pressure

Binding energy, electronic states, and optical absorption in a staircase-like spherical quantum dot with hydrogenic impurity

Binding energy, electronic states, and optical absorption in a staircase-like spherical quantum dot with hydrogenic impurity

Effect of number of well and core radius on the binding energy and optical properties of multishell spherical quantum dot with parabolic potential

In the current study, the probability densities and binding energy of the ground state and first excited sate in multishell quantum dot with parabolic confinement potential have been examined. Also, the effects of core radius, the number of well in structure and the presence of impurity on the total optical absorption coefficient have been investigated. The finite difference method has been used to obtain the energy levels and related wave functions of the system within framework effective mass approximation. The results obtained reveal that the number of well, especially the first five values, have a considerable impact on the critical core values of binding energy. It is found that the presence of impurity and the number of wells cause a blue shift in the peak positions of total absorption coefficients. Moreover, our results show that these factors have an important effect on the magnitude of optical properties.

Calculation of Intradonor Normalized Transition Energy in Spherical Quantum Dots Made of Different Materials

Under the effective mass approximation, the binding energies, transition energies between 1s and 1p states, and normalized transition energies of spherical quantum dots made of different materials are calculated using the variational method. In particular, binding, transition, and normalized transition energies are examined depending on the radius of the quantum dot and the position of the hydrogenic impurity. It is observed that the binding energy and transition energy decrease as the radius of the quantum dot increases, whereas the normalized transition energy increases. In all four different structures, it is seen that the binding energy first reaches a maximum and then starts to decrease according to the position of the hydrogenic impurity. In contrast, the transition energy behaves almost the opposite. Additionally, when the change of the normalized transition energy is examined according to the impurity position, it is determined that it decreases up to the value of ri/R = 0.6 and then remains almost constant. According to our literature review, the normalized transition energy for the four different quantum dots is calculated for the first time in this study.

Inserting self-assembled InAs quantum dots into quantum cascade lasers to achieve a broadband free-running frequency comb and effective radio-frequency injection.

We present what we belive to be a new band design in which self-assembled InAs quantum dots (QD) are embedded in InGaAs quantum wells (QW) to fabricate broadband single-core quantum dot cascade lasers (QDCLs) operating as frequency combs. The hybrid active region scheme was exploited to form upper hybrid QW/QD energy states and lower pure QD energy states, which expanded the total laser bandwidth by up to 55 cm-1 due to a broad gain medium provided by the inherent spectral inhomogeneity of self-assembled QDs. The continuous-wave (CW) output power of these devices was as high as 470 mW with optical spectra centered at ∼7 µm, which allowed CW operation at temperatures up to 45 °C . Remarkably, measurement of the intermode beatnote map revealed a clear frequency comb regime extending over a continuous 200 mA current range. Moreover, the modes were self-stabilized with intermode beatnote linewidths of approximately 1.6 kHz. Furthermore, what we believe to be a novel π-shaped electrode design and coplanar waveguide transition way were used for RF signal injection. We found that RF injection modified the laser spectral bandwidth by up to 62 cm-1. The developing characteristics indicate the potential for comb operation based on QDCLs as well as the realization of ultrafast mid-infrared pulse.

Phase and Thermal-Driven Transport Across T-Shaped Double Quantum Dot Josephson Junction

The phase and thermal driven transport properties of the T-shaped uncorrelated double quantum dot Josephson junction are analyzed by using Keldysh non-equilibrium Green's function equation of motion technique. In this setup, we have shown that the side-attached quantum dot provides an additional route for electron transmission which is affecting the transport properties by adjusting the interdot hopping between the main dot and the side dot. We began with investigating the impact of interdot hopping on Andreev bound states and Josephson supercurrent. When a small thermal bias is applied across the superconducting leads, the system exhibits a finite thermal response which is primarily due to the, thermally induced, quasi-particle current. The behavior of the Josephson supercurrent and the quasi-particle current flowing through the quantum dots is examined for various interdot hopping and thermal biasing. Finally, the system is considered in an open circuit configuration where the thermally driven quasi-particle current is compensated by the phase-driven Josephson supercurrent and the thermophase effect is observed. The effect of interdot hopping and the position of quantum dot energy level on the thermophase Seebeck coefficient is investigated

The impact of the electric field on the photoionization cross section, polarizability, and donor impurity binding energy in multilayered spherical quantum dot

The impact of the electric field on the photoionization cross section, polarizability, and donor impurity binding energy in multilayered spherical quantum dot

Cobalt-doped CsPbBr3 perovskite quantum dots for photoelectrocatalytic hydrogen production via efficient charge transport

Photoelectrochemical cells (PECs) based on all-inorganic perovskite quantum dots (QDs) have great potential for the catalytic splitting of water using sunlight due to their good photovoltaic properties and inexpensive manufacturing process. However, their development is severely constrained by their own large carrier transport barriers and poor water stability. Herein, we report the synthesis of cobalt doped CsPbBr3 perovskite quantum dots (Co-doped CsPbBr3 QDs) by hot-injection method and their preparation into FTO/c-TiO2/m-TiO2/Co-CsPbBr3 QDs photoanode devices, and further encapsulation of the devices using low-temperature conductive carbon paste (LTCC). The partial replacement of Pb2+ sites by Co2+ in Co-doped CsPbBr3 QDs with appropriate concentrations enhances the binding energy of QDs, forms impurity energy levels, reduces carrier transport barriers, improves carrier lifetime and carrier separation and transport rate, so as to improve optoelectronics purpose of catalytic activity. Ultimately, the Co-CsPbBr3 QDs photoanode produced 1.944 mA cm−2 at 1.23 VRHE under simulated sunlight (AM 1.5, 100 mW cm−2) and achieved a stable photocurrent density of more than 1 mA cm−2 for up to 5500 s in aqueous KOH solution. The development of effective all-inorganic perovskite quantum dots sheds light on the realization of catalysts for PEC water splitting.

Interference effects in coupled triple quantum dot systems

Electronic transport through a coupled triple quantum dot (TQD) system is theoretically studied using Equilibrium Green’s function approach. The TQD system is systematically investigated for T-shape configuration and triangular shape configuration. T-shape (triangular shape) configuration corresponds to the TQD structure in which two quantum dots (QD)s are connected to the left and right leads in series and third one is side coupled to the right one (both) the QDs. In the electronic transmission spectrum of T-shape configuration, it is found that an antiresonance peak occurs at the QDs energy level and width of the peak increases with the increase in the tunnel coupling of the side coupled QD. Further, an asymmetric Fano lineshape is also observed while investigating transition from the T-shape to the triangular shape configuration. Interestingly, this Fano peak is found to occur when side coupled QD is weakly coupled to both the serially coupled QDs and its appearance becomes more prominent when the side coupled QD is symmetrically coupled to both the QDs. Both these effects reveal quantum interference effects that take place between discrete states and the continuum in electron transport through multiple channels in T-shape and triangular shape geometries.

Revealing Atomic‐Level Surface Passivation of PbI2‐Reconditioned Red Perovskite Quantum Dots

AbstractCsPbI3 perovskite quantum dots (QDs) are promising materials for high‐efficiency and low‐cost red fluorophores in advanced display and light‐sensing applications. However, structural and spectral stabilities of CsPbI3 QDs by traditional preparation are seriously broken in water or light environment. Here, a compositional engineering strategy with an additional PbI2‐recondition process to synthesize highly‐stable CsPbBr1.2I1.8 @ SiO2 QDs is demonstrated. Time‐ and temperature‐dependent photoluminescence and Raman measurements prove that spectral stability and exciton binding energy of QDs are greatly improved within this strategy. Notably, high‐resolution structure characterizations, point‐to‐point diffraction patterns and line‐scanning of element distributions provide strong and direct evidence at atomic‐level to reveal that PbI2‐recondition can repair defects well, which helps to construct perfect lattices and homogeneous SiO2 passivation layers to prevent the surface bonding of molecules. Moreover, our red perovskite QDs are further designed to prepare various anti‐counterfeiting labels as multi‐scale complex patterns to store and protect information. The proposed recondition strategy explores a new avenue to prepare stable and high‐quality red perovskite QDs for new‐generation lighting and light‐sensing devices.

Effect of energy level configuration on storage of optical solitons in InAs/GaAs quantum dot electromagnetically induced transparency medium

Based on the current growth technology of quantum dot in the experiment, considering that the probe fields and control fields at different frequencies are coupled between different energy levels of the InAs/GaAs quantum dot, the ladder-type, Λ-type and V-type energy level configurations can be formed. The linear and nonlinear properties of these energy level configurations of InAs/GaAs quantum dots are studied by using semiclassical theory combined with multiple scale method. It is shown that in the linear case, electromagnetic induction transparency windows can be formed among ladder-type, Λ-type and V-type energy level configurations. And the width of the transparent window increases with the strength of the control pulse increasing. For the nonlinear case, under the current experimental condition, optical solitons can be formed and stored in ladder-type configuration and <inline-formula><tex-math id="M6">\begin{document}$ {{\Lambda }} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20221965_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20221965_M6.png"/></alternatives></inline-formula>-type energy level configuration. However, optical solitons cannot be formed in the V-type energy level configurations, which is because the nonlinear effect of the system is very weak. Furthermore, it is demonstrated that the fidelity of the storage and retrieval of the optical solitons is higher than that of linear optical pulse and strongly nonlinear optical pulse. Interestingly, it is also found that the amplitude of stored optical solitons in <inline-formula><tex-math id="M8">\begin{document}$ {{\Lambda }} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20221965_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20221965_M8.png"/></alternatives></inline-formula>-type energy level configuration is higher than that in ladder-type energy level configuration. This study provides a theoretical basis for semiconductor quantum dot devices to modulate the amplitude of the stored optical solitons.

Nano‐Confined Growth of Perovskite Quantum Dots in Transparent Nanoporous Glass for Luminescent Chemical Sensing

AbstractPrior nano‐confined matrices for perovskite quantum dots (QDs) dealt only with powders or thin films, which usually suffer from poor handling properties and high transparency limitations for integrating into optical devices. Here, the nano‐confined growth of perovskite QDs in an optically transparent, robust, and monolithic matrix by using nanoporous glass (NG) as a nano‐reactor is demonstrated. Owing to quantum confinement effects in the inherent nanoporous network, rapid nanoconfined low‐temperature solution‐processed perovskite QDs could synthesize spontaneously. The binding energy of CsPbBr3 QDs in NG has been enhanced to ≈177.2 meV due to the confinement effect. The nano‐channels enable the tunable mono/multi‐color emission in full visible range via pore size tailoring or post‐halide exchange. Considering the fast diffusion of nanoporous channels and enhanced stability in this processable monolithic composite, a rapid‐response and reusable red‐green switching light‐emitting diode (LED) sensor for halomethanes is demonstrated. The rational design of perovskite NG via this efficient nano‐confined route results in a new optoelectronic device‐relevant material platform.

Construction of efficient electrochemiluminescence resonance energy transfer sensor based on SnO2/SnS2QDs-Ru@IRMOF-3 composite for sensitive detection of procalcitonin.

An efficient electrochemiluminescence resonance energy transfer (ECL-RET) method is proposed which combines the luminescent materials of tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) (energy donor) and tin dioxide and tin disulfide quantum dots (SnO2/SnS2QDs) (energy acceptor) into the isoreticular metal - organic framework-3 (IRMOF-3) material to form a composite. In this mode, the distance between the energy donor and the acceptor was greatly shortened, reducing the energy loss, and thereby effectively improving RET efficiency and further significantly improving the ECL signal. The obtained composite (SnO2/SnS2QDs-Ru@IRMOF-3) was combined with sandwich immunoreaction to construct an ECL immunosensor for the sensitive detection of procalcitonin (PCT). Under the optimized experimental conditions with a working potential of - 1.48V (vs Ag/AgCl), the proposed PCT biosensor exhibited a linear concentration range of 1 × 10-4-200ngmL-1, with a detection limit of 0.029pgmL-1 (S/N = 3). The biosensor was used to detect PCT in actual samples. The biosensor has broad application prospects in biological analysis and clinical diagnosis due to its high sensitivity, good selectivity, and good stability.

Quantum Mechanical Analysis Based on Perturbation Theory of CdSe/ZnS Quantum-Dot Light-Emission Properties.

A simulation of quantum dot (QD) energy levels was designed to reproduce a quantum mechanical analytic method based on perturbation theory. A Schrödinger equation describing an electron–hole pair in a QD was solved, in consideration of the heterogeneity of the material parameters of the core and shell. The equation was solved numerically using single-particle basis sets to obtain the eigenstates and energies. This approach reproduced an analytic solution based on perturbation theory, while the calculation was performed using a numerical method. Owing to the effectiveness of the method, QD behavior according to the core diameter and external electric field intensity could be investigated reliably and easily. A 9.2 nm diameter CdSe/ZnS QD with a 4.2 nm diameter core and 2.5 nm thick shell emitted a 530 nm green light, according to an analysis of the effects of core diameter on energy levels. A 4 nm redshift at V/cm electric field intensity was found while investigating the effects of external electric field on energy levels. These values agree well with previously reported experimental results. In addition to the energy levels and light emission wavelengths, the spatial distributions of wavefunctions were obtained. This analysis method is widely applicable for studying QD characteristics with varying structure and material compositions and should aid the development of high-performance QD technologies.

Study of photoionization cross section and binding energy of shallow donor impurity in multilayered spherical quantum dot

In the framework of the effective mass approximation and by using the finite element method , we have studied the simultaneous effects of position dependent effective mass (PDEM) and dielectric function on the shallow donor impurity binding energy and photoionization cross section in a multilayered spherical quantum dot . We have also investigated the influence of conduction band nonparabolicity and polaronic mass on the both binding energy and photoionization cross section (PCS). The obtained results have shown that the nonparabolicity and polaronic mass effects enhance the binding energy and photoionization cross section. Furthermore, it can be concluded from this research that the binding energy and the PCS are strongly dependent on the geometrical parameters, and PDEM. Changes in binding energy and photoionization cross section have physical reasons, which are discussed in details. • The photoionization cross section (PCS) and the binding energy are strongly dependent on the width of the structure layers. • The conduction band nonparabolicity and the polaronic mass effects enhance the binding energy and reduce the PCS peak magnitude. • The dependence of the dielectric function ε ( r ) on the electron coordinates makes the amplitude peak of the PCS take high values.