Area Of Quantum Dots Research Articles

77‐2: Quantum‐Dot Color Conversion Achieved by A Novel Structure of Hollow Cylindrical Blue MicroLED

This study proposes a novel design for achieving color conversion in micro light‐emitting diodes (Micro‐LEDs) using a hollow cylindrical structure. Instead of printing quantum dots (QDs) on the upper surface of the Micro‐LEDs, QDs are printed in a hollow place created by designing hollows of varying sizes and applying a layer of highly reflective metal to the top and outer walls. The design of this structure confines the emission light to the hollows, reduces photon leakage, and increases the path length of the excitation light in the quantum dot area. The color conversion capabilities of 60, 70, 80, and 90 μm hollows were investigated, and a 3×3 array was demonstrated. Using this approach, the thickness of the quantum dots on the upper surface of the LED can be reduced, without the need for a thick black matrix for reducing the problem of light crosstalk. This hollow cylindrical design presents a promising new approach for achieving color conversion in Micro‐LEDs, with potential applications in displays and lighting technologies.

P‐10.9: Quantum Dot Color Conversion Achieved by A Novel Structure of Hollow Cylindrical Blue Micro‐LED

This paper proposes a novel approach to achieve color conversion in micro light-emitting diodes (Micro-LEDs) using a hollow cylindrical design, which allows the printing of quantum dots (QDs) in a hollow place. By varying the sizes of the hollows and applying a highly reflective metal layer to the top and outer walls, the emission light can be confined to the hollows, reducing the leakage of photons and increasing the path length of the excitation light in the quantum dot area. We investigated the color conversion capabilities of 60, 70, 80, and 90 um hollows, and demonstrated a 3x3 array. This approach reduces the thickness of the quantum dots on the LED surface and eliminates the need for a thick black matrix, thereby reducing the problem of light crosstalk. This hollow cylindrical design has potential applications in displays and lighting technologies.

Charging graphene nanoribbon quantum dots

We describe charging a quantum dot induced electrostatically within a semiconducting graphene nanoribbon by electrons or holes. The applied model is based on a tight-binding approach with the electron-electron interaction introduced by a mean field local spin density approximation. The numerical approach accounts for the charge of all the $p_z$ electrons and screening of external potentials by states near the charge neutrality point. Both a homogenous ribbon and a graphene flake embedded within the ribbon are discussed. The formation of transport gaps as functions of the external confinement potential (top gate potential) and the Fermi energy (back gate potential) are described in good qualitative agreement with the experimental data. For a fixed number of excess electrons we find that the excess charge added to the system is, - depending on the voltages defining the work point of the device: $(i)$ delocalized outside the quantum dot, - in the transport gap due to the top gate potential $(ii)$ localized inside the quantum dot, - in the transport gap due to the back gate potential or $(iii)$ extended over both the quantum dot area and the ribbon connections, - outside the transport gaps. The applicability of the frozen valence band approximation to describe charging the quantum dot by excess electrons is also discussed.

Magnetic polaron formation in graphene-based single-electron transistor

We theoretically study the magnetic polaron (MP) formation in a ferromagnetic graphene single-electron transistor (SET), which consists of a graphene quantum dot (QD) between two insulating layers, i.e., a ferromagnetic insulator EuO and a nonmagnetic substrate such as SiC. In the lateral direction, the QD is electrically coupled to source, drain and gate electrodes, so that the number of electrons can be controlled by the gate voltage. Due to a proximity effect at the EuO/graphene interface, i.e., the exchange interaction between the charge carriers in graphene and the localized magnetic electrons in EuO, there is a magnetic coupling between the graphene QD and EuO. Using Green's function technique an expression for the total free energy of the SET is derived, which is then minimized at the given temperature and gate voltage. This leads to the MP formation and a consequent local enhancement of the ferromagnetic properties of EuO at the EuO/graphene interface. The MP formation is enforced by the large Coulomb interaction between the carriers in graphene. The spin polarization at the graphene/EuO interface in the QD area can be controlled by the gate voltage of the SET.

Voltage–capacitance and admittance investigations of electron states in self-organizedInAs/GaAs quantum dots

Emission of electrons from localized electron states in InAs/GaAs self-organized quantumdots (QDs) grown by MOCVD has been studied by a combination of steady-statevoltage–capacitance and admittance techniques. We have found a fine structure of carrierconcentration profile in the area of QDs, which may be attributed to ground and excitedenergy states of electrons in the QDs. The total range of activation energies detected in theadmittance investigations extends from 20 meV up to 140 meV and testifies to thesignificant inhomogeneous broadening of the density of state function due to the QDscattering in geometric sizes.

A fast configuration space method for solving local Kohn–Sham equations

This paper describes algorithmic components of a program package for solving the Kohn–Sham equations in coordinate space. The primary application is envisioned to be in the area of quantum dots and metallic clusters, where basis function expansions are difficult to apply. A number of techniques are introduced for solving different aspects of the problem: the eigenvalue problem is solved by using a fourth order factorization of the evolution operator e − ϵH , which is significantly more efficient than the conventional second order factorization. The wave functions are orthogonalized using a subspace orthogonalization procedure generating a noticeably faster convergence than the conventional Gram–Schmidt orthogonalization method. The self-consistency problem arising from the non-linearity of the Kohn–Sham equations is solved with a Newton–Raphson procedure, which is shown to be equivalent to linear response theory. A collective approximation for the static density–density response function, rooted in Feynman’s theory of excitations in quantum fluids, leads to a version of the algorithm that maintains the convergence properties and only needs the computation of occupied states of the system. This approximation makes the implementation of the algorithm in three dimensions practical. Converged solutions are obtained from very rough guesses within a view iterations. The method is applied to two-dimensional quantum dots with random impurities and to metal clusters. We report statistical properties of ionization and excitation energies of spin-polarized quantum dots and optimized structural properties of small Na clusters.