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Regardless of the fact that the confirmed Power Conversion Efficiency (PCE) of kesterite materials for photovoltaic cells is lower than that of other chalcogenide materials, there is still sign of improvement due to their high absorption rate, flexibility to have a tunable bandgap, abundance in nature, and so on.The primary objectives of this study was to assess the combined utilisation of quantum dots and quantum wells in kesterite material. This was achieved through three key approaches: firstly, by altering the quantity of quantum dots and wells present in the nanostructure; secondly, by modifying the composition of the dots and well material through adjustments in the Sulphur and Selenium ratio of CZTSSe. The third aspect to consider is the analysis of the effect of changes in operating temperature on high-performing nanostructures, building upon the information gathered from the previous two processes. Electrical properties such as PCE, $ V_{oc}$ , $ J_{sc}$ , and IV curve have been analyzed so that the performance of the hybrid structure can be examined. A quantum well and a quantum dot layer are both present in the p-i-n structure. The quantum dot layer is composed of ten quantum dots placed in an array. The effects of quantum dot thickness (5 and 10 nm) were also investigated. According to the findings, as few as three quantum dot layers and three quantum wells resulted in a 21% PCE. By varying the operating temperature between 250 K to 500 K, the temperature dependency of high-PCE structures was examined. [ABSTRACT FROM AUTHOR]

This work presents the impact of barrier spacer on the structural and optical properties of strain-coupled Stranski-Krastanov (SK) on Sub Monolayer (SML) quantum dot (QD) heterostructures. Various ternary and quaternary materials have been employed as the barrier layer of SK-SML QD heterostructures. In the coupled SK-SML QDs, the residual strain propagates from the SML seed layer towards the top SK dots, introducing defects and dislocations. After employing the ternary (GaAs1-ySby) and quaternary (InxAl0.21Ga1-.0.21-xAs and In0.18Ga0.82As1-ySby) materials, the residual strain reduces, reducing the defects which thereby helps in increasing the crystalline quality of the heterostructure. Nextnano software has been used to compute the structures' strain, energy band profile, probability density functions, and emission wavelength. Two strain components, viz. hydrostatic as well as biaxial strain, have been computed and compared for all the heterostructures to understand the distribution of the strain profile. The emission wavelength is red-shifted for the SK-SML QD heterostructures with ternary and quaternary materials as a barrier layer as compared to that of the GaAs barrier. Moreover, type-I and II energy band profiles are observed for Sb-based barrier material, appropriate for various optoelectronic applications. This is a comparative study of SK-SML QDs with various barrier materials helps minimize the strain and defects and improve the device performance. [ABSTRACT FROM AUTHOR]

We propose a new method for fabricating arrays of colloidal quantum dots for color conversion layers (CCLs) with atomic layer deposited (ALD) encapsulation. Semiconductor processes were used to transfer the CCL onto a transparent glass substrate. This method enables pixels as small as 5 μm, and the pixel's size and pitch can be controlled through the semiconductor process and mask layout. A dual-color array with a red-and-green CCL was also demonstrated to be suitable for microdisplay applications in experiments. The best color conversion efficiency of a single color CCL reached as high as 20.7%. A set of distributed Bragg reflector mirrors was used to increase photon recycling, and these mirrors yielded an increase in peak intensity of 35.7%. We formulated a model of incoherent reflection and transmission to calculate the changes in CCL properties when mirrors are added; this model had close fit with results from experiments in which mirrors of different reflection coefficients were used. Through the use of ALD, the CCL can be stored at a normal room-temperature environment for more than 9000 hours, and the projected lifetime is linearly extrapolated to be 44,041 hours.

We numerically analysed the single mode stability of of multi quantum well and quantum dot DFB laser diodes in the presence of external optical feedback. Laser diodes which operate in a stable single mode in the absence of feedback were found to sometimes become multimode for external feedback levels below −30 dB. This is even the case for lasers with zero linewidth enhancement factor, even though such lasers are sometimes touted as feedback insensitive. The behavior depends strongly on the phase of the external reflection, as well as on the specific DFB laser structure.

This paper investigates the effects of high magnetic field on electrical treeing of silicone rubber (SiR). Experimental results show that electrical trees are more easily to be initiated and spread further along the direction of electric field under the effects of high magnetic field. When the direction of high magnetic field is perpendicular to that of electric field, magnetic field with higher magnetic flux density also results in larger accumulated damage area. Splitting of energy band structure and changes in polarization characteristics result in a lower interface barrier and more serious partial discharge, thus causing the weakened resistance to electrical treeing in high magnetic field. Based on the insulation degradation mechanism, SiR was modified by adding ferroferric oxide (Fe3O4) nanoparticles to improve its insulation performance in high magnetic field. Moderate addition amount of Fe3O4 nanoparticles is proved to be able to suppress electrical treeing in high magnetic field by forming quantum dots, modifying polarization properties and partial discharge behavior. Excessive addition of Fe3O4 nanoparticles has negative effects on suppressing electrical treeing due to the magnetization of the nanocomposites.

We report the fabrication and electrical characterization of single-hole transistors (SHTs), in which a Ge spherical quantum dot (QD) weakly couples to self-aligned electrodes via self-organized tunnel barriers of Si3N4. A combination of lithographic patterning, sidewall spacers, and self-assembled growth was used for fabrication. The core experimental approach is based on the selective oxidation of poly-SiGe spacer islands located at the specially designed included-angle locations of Si3N4/Si-trenches. By adjusting processing times for conformal deposition, etch back and thermal oxidation, good tunability in the Ge QD size and its tunnel-barrier widths were controllably achieved. Each Ge QD is electrically addressable via self-aligned Si gate and reservoirs, thus offering an effective building block for implementing single-charge devices.

A Sn-ball was integrated with a colloidal quantum dot light-emitting diode package to achieve effective heat and reliability management. The electric, optical intensity, and heat distributions of the package were evaluated under various radiant fluxes; data were collected at the 90th hour of aging. Under 1 W/cm2, the areal temperature decreased from 38.5 °C (without Sn-ball) to 32.3 °C (with Sn-ball), which helped extend the lifetime of the colloidal quantum dots in the package. Specifically, the introduction of the metal ball structure engendered a two- to three-fold increase in lifetime. The study findings could contribute toward integrating quantum dots into photonic devices.

We observe rich phenomena of two-level random telegraph noise (RTN) from a commercial bulk 28-nm p-MOSFET (PMOS) near threshold at 14 K, where a Coulomb blockade (CB) hump arises from a quantum dot (QD) formed in the channel. Minimum RTN is observed at the CB hump where the high-current RTN level dramatically switches to the low-current level. The gate-voltage dependence of the RTN amplitude and power spectral density match well with the transconductance from the DC transfer curve in the CB hump region. Our work unequivocally captures these QD transport signatures in both current and noise, revealing quantum confinement effects in commercial short-channel PMOS even at 14 K, over 100 times higher than the typical dilution refrigerator temperatures of QD experiments (< 100 mK). We envision that our reported RTN characteristics rooted from the QD and a defect trap would be more prominent for smaller technology nodes, where the quantum effect should be carefully examined in cryogenic CMOS circuit designs. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) are ideal color-conversion materials for display fields. Preparation of micro-nanostructures is a mainstream method for obtaining a high photoluminescence (PL) intensity. Electrical induction, a method of preparing micro-nanostructures, was introduced to obtain QD films with high PL performance by preparing a sandwich column array structure (SCAS). By changing the spacer thickness, a series of SCAS-QD films were fabricated, after optimizing the voltage. The SCAS-QD layers with a 25- $\mu \text{m}$ spacer obtained the maximum PL enhancement of green light intensity: up to 42.8%. The enhancement was caused by the microcavity trapping and light extraction effects. The former could increase the utilization factor of blue light and the latter could increase the emission probability of green light. This is a simple, high-efficient, and low-cost method for preparing QD films with high PL performance without increasing the QD concentration. [ABSTRACT FROM AUTHOR]

In this study, we propose a centrifugation packaging (CP) structure to enhance the optical and thermal dissipation performance of LEDs, using SBA-15 particles to facilitate the sedimentation and dispersion of QDs. The results indicate that the EL spectra of the LEDs remains almost unchanged after the centrifugation time of 60 min and a CP structure can be obtained. The radiation power and luminous flux of LEDs with a CP structure improve by 9.1% and 10.4%, respectively, compared with the uniform distribution (UD) structure. The surface temperature of LED devices with the CP structure is reduced to 34.4 °C from 41.8 °C at a current of 100 mA. Furthermore, the simulation results show that the maximum temperature in the CP structure is 22.4% lower than that in the UD structure at a current of 500 mA. Thus, this study can provide a new perspective for designing settlement structures of QD–LEDs to enhance their optical and thermal performance. [ABSTRACT FROM AUTHOR]

This paper is a report on the mathematical analysis and working principle of a wide color gamut autostereoscopic 2D-3D switchable display based on the dynamic subpixel arrangement method. The display prototype discussed in the paper has three major distinctions. First, the use of dynamic subpixel arrangement method and eye-tracking system has improved its performances in the resolution, crosstalk and 2D/3D switching statistics. Second, a design of Quantum-Dot-Polymer (QDP) film and optical layer combined backlight has enhanced its viewing angle and color gamut. Third, the application of parallel computing to the dynamic subpixel arrangement method has improved its real-time performance. Base on observation from finished fabrication and experiment, this prototype has already demonstrated noticeable enhancement in terms of color gamut expansion-reaching 77.98% according to ITU-R Recommendation BT.2020 (Rec.2020), and crosstalk reduction-with the minimum crosstalk rate at nearly 6%. Close comparison with two other commercial 3D displays (BENQ XL2707-B and View Sonic VX2268WM) are also presented in the paper for sufficiency.

In this letter we report a method for numerically determining the spontaneous polarization (PSP) of, non-periodic, 3-dimensional wurtzite structures, for the case of nanoparticles (NPs). Using this numerical model, we solve for the PSP of GaN, ZnO, and 2H-SiC NPs with radii ranging from 1 nm to 100 nm. This leads us to the result that wurtzite NPs theoretically display very large and difficult to control PSP. In which even a tenth of a nm added or subtracted to the NP radius can have a such a large impact on the PSP of the NP that it can switch the usually negative wurtzite PSP to positive or vise versa. [ABSTRACT FROM AUTHOR]

As a scintillating material, colloidal quantum dots (cQDs) are proving to be a promising alternative to traditional organic fluorophores used for radiation detection. By varying the size and composition of the cQDs, their physical and optical properties can be controlled. Furthermore, through appropriate functionalization of the cQD surface, they can be easily integrated within a variety of matrices, making them an appealing choice for the development of a new generation of scintillation dosimeters. In this article, three types of cQDs are incorporated in polystyrene to produce nanocomposite optical fibers, and their response to 6-MV X-rays is investigated. All fibers show a linear response with delivered dose, minimal dependence on the linac dose rate, and for the case of the CdSe/CdS cQD-doped fiber, a reasonable resistance to radiation-induced signal degradation. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots are currently emerging as one of the most promising sources of non-classical light on which to base future quantum networks. They can generate single photons as well as pairs of entangled photons with unprecedented brightness, indistinguishability, and degree of entanglement. These features have very recently opened up the possibility to perform advanced quantum optics protocols that were previously inaccessible to single quantum emitters. In this work, we report on two experiments that use the non-local properties of entanglement to teleport quantum states: three-photon state teleportation and four-photon entanglement teleportation. We discuss all the experimental results in light of a theoretical model that we develop to account for the non-idealities of the quantum source. The excellent agreement between theory and experiment enables a deep understanding of how each parameter of the source affects the teleportation fidelities and it pinpoints the requirements needed to overcome the classical limits. Finally, our model suggests how to further improve quantum-dot entangled-photon sources for practical quantum networks. [ABSTRACT FROM AUTHOR]

The size effect on the electronic structure and optical properties of cubic CsPbBr3 perovskite quantum dots is investigated by using an 8-band ${k}\cdot{p} $ model based on effective-mass envelope function theory with exciton binding energy consideration. Quantum dots with smaller size have larger bandgaps due to quantum confinement. The transition matrix element (TME) is also influenced by the size. The optical gain of such material is calculated by considering TME, Fermi factor, injected carrier density, quantum dot size, and dephasing rate. Higher density of injected carrier is needed for smaller quantum dot to get a positive optical gain. The peak of optical gain has a blue shift as the size of quantum dot decreases. When the carrier density increases for a quantum dot with certain size, a blue shift in emission peak position can be observed due to band filling effect. Smaller quantum dots have higher differential optical gain at carrier densities within certain range. [ABSTRACT FROM AUTHOR]

A new electrochemical sensor based on CdSe quantum dots-multiwalled carbon nanotube composite film (CdSeQDs-cMWCNTs) was developed for highly selective simultaneous determination of 1,4-dihydroxybenzene (hydroquinone, HQ) and 1,2-dihydroxybenzene (catechol, CC) in 0.1 M phosphate buffer solution (pH 7.4). CdSeQDs-cMWCNTs/GCE exhibited two well-distinguished anodic peaks with large currents for simultaneous detection of HQ and CC in comparison with bare GCE and cMWCNTs/GCE. Furthermore, CdSeQDs-cMWCNTs/GCE has an excellent anti-interference ability for the detection of HQ and CC in the presence of some inorganic compounds and phenol derivatives. Under the optimized condition, CdSeQDs-cMWCNTs/GCE showed wide linear responses from $0.5~\mu \text{M}$ to $110~\mu \text{M}$ for HQ, and from $0.5~\mu \text{M}$ to $110~\mu \text{M}$ for CC, with the detection limits of $0.35~\mu \text{M}$ and $0.25~\mu \text{M}$ , respectively. CdSeQDs-cMWCNTs/GCE was successfully applied to the simultaneous determination of HQ and CC in tap water with satisfactory recovery. [ABSTRACT FROM AUTHOR]

We demonstrated automatic cross carrier-envelope phase locking between two synchronized pulse trains at different wavelengths generated within a single InAs/InP quantum-dot diode laser cavity. The resulting waveforms, verified by optical auto-/cross-correlation and explained by a theoretical model, show multipeaks or quasi-periodic subpulses with a central-subpulse pulse duration of about 183 fs. [ABSTRACT FROM AUTHOR]

We compare the timing jitter of a mode-locked InAs/InP quantum dash (QD) coherent comb laser (CCL) with and without an external cavity self-injection feedback locking (SIFL) system. The jitter is determined through a measurement of the first harmonic of the RF power spectrum of the laser output detected using a fast photodiode. A significant reduction in timing jitter is observed in the laser with the external cavity SIFL. A pulse to pulse root-mean-square time jitter of 1.56 fs is achieved for the laser with the external cavity SIFL. This low timing jitter is a promising light source for the next generation high-speed coherent networking systems and all-optical signal processing. We demonstrate results of a double polarization 16-QAM data format transmission system at a symbol rate of 25 GBd using more than 30 individual channels of the QD CCL. An error vector magnitude of 5.8% and bit error rate of 3.0 × 10–9 were obtained. And, 6.0 Tb/s (16QAM 30 × 25 Gbd PDM) coherent transmission is achieved. [ABSTRACT FROM AUTHOR]

We investigated the optical gain properties and lasing characteristics of a pulsed electrically pumped laser structure, which consists of a single layer of self-assembled InP quantum dots (QDs) assembled in (Al0.10Ga0.90)0.52In0.48P barriers. The optical gain and absorption spectra were obtained by analyzing the amplified spontaneous emission as a function of the excitation length. At a current density of 1.2 kA/cm2, an internal optical loss value of 5 ± 2 cm $^{{-1}}$ and a peak modal gain of 39.3 cm $^{{-1}}$ corresponding to a material gain of approximately 2675 cm $^{{-1}}$ per QD layer were determined at room temperature. For a 2.24-mm-long laser with uncoated facets emitting at 660 nm, a low threshold current density of 281 A/cm2 and an external differential quantum efficiency of 34.2% were determined. The internal quantum efficiency of 66% and the transparent current density of 65.8 A/cm2 for a single layer of QDs were also demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a new class of resonant tunneling diodes (RTDs) that are planar and realizable with a single graphene nanoribbon. Unlike conventional RTDs, which incorporate vertical quantum well regions, the proposed devices incorporate two confined planar quantum dots within the single graphene nanoribbon, giving rise to a pronounced negative differential resistance (NDR) effect. The proposed devices, termed here as planar double-quantum-dot RTDs, and their transport properties are investigated using quantum simulations based on nonequilibrium Green's function formalism and the extended Huckel method. The proposed devices exhibit a unique current-voltage waveform consisting of a single pronounced current peak with an extremely high, in the order of 104, peak-to-valley ratio. The position of the current peak can be tuned between discrete voltage levels, allowing digitized tunability, which is exploited to realize multi-peak NDR devices.

This paper reports an optical “TURN OFF” aptasensor, which is comprised of a deoxyribonucleic acid aptamer attached to a quantum dot on the $5^{\prime }$ terminus and gold nanoparticle on the $3^{\prime }$ terminus. The photoluminescence intensity is observed to decrease upon progressive addition of the target protein tumor necrosis factor-alpha (TNF- $\alpha $) to the sensor. For PBS-based TNF- $\alpha $ samples, the beacon exhibited 19%–20% quenching at around 22 nM concentration. The photoluminescence intensity and the quenching efficiency showed a linear decrease and a linear increase, respectively, between 0 to 22.3 nM TNF- $\alpha $. The detection limit of the sensor was found to be 97.2 pM. Specificity test results determined that the sensor has higher selectivity toward TNF- $\alpha $ than other control proteins such as C—reactive protein, albumin, and transferrin. The beacon successfully detected different concentrations of TNF- $\alpha $ in human serum-based samples exhibiting around 10% quenching efficiency at 12.5 nM of the protein. [ABSTRACT FROM AUTHOR]

General and versatile ligand exchange routes are developed for converting nonpolar solvent soluble quantum dots to alcohol-soluble. Through ligand exchange, long-chain methyl-terminated oleylamine on quantum dots’ surface can be substituted by short-chain hydroxyl-terminated 6-mercaptohexanol, enabling their dispersibility in polar organic solvents including methanol, ethanol, isopropanol, and dimethylformamide. The resulted alcohol-soluble quantum dots maintained their optical properties and perfectly fit the requirements for solution-processed electroluminescence devices. Light emitting diode based on the alcohol-soluble quantum dots eclipsed their counterparts made from nonpolar solvent soluble quantum dots. The improvement of device performance is ascribed to decreased energy barriers and increased charge injection rate between charge transport layer and the emitting layer. The hydroxyl-terminated quantum dots provide a new materials platform for the design of highly efficient quantum dot light emitting diodes, and also enable an alternative route to achieve RGB display devices. [ABSTRACT FROM PUBLISHER]

In recent years, quantum dots (QDs) have been widely studied because of their precisely tunable, narrow, and strong emission. Different kinds of light-emitting diodes (LEDs) have been fabricated by QDs, and it is desirable to utilize QD-LEDs to form the next-generation display. Here, we review a few key technologies in the area of QD-LED displays, including the compositions and the structures of the QDs, the methods of forming QD layers, and the architectures, crosstalk, and encapsulations of the QD-LEDs. [ABSTRACT FROM PUBLISHER]

This paper presents nonvolatile memory characteristics of a quantum dot gate floating gate nonvolatile memory (QDNVM) that employs SiOx-cladded silicon quantum dots as discrete charge storage nodes of the floating gate. The cladding of Si quantum dots and control of their size are shown to result in a faster access and improved retention time. The floating gate is formed by site-specific self-assembly of SiOx-Si quantum dots on the tunnel oxide layer over the p-region between source and drain of an n-channel field-effect transistor (FET). Experimental data on fabricated long channel devices show threshold voltage shift as a function of duration and magnitude of the electrical stress applied during the “Write” operation. Current–voltage characteristics ( I\mathrm {D} – V\mathrm {D} and ID – VG) are presented before and after stress. The electrical characteristics are explained using a quantum dot gate FET model which includes the threshold voltage shift ( \Delta \textV\mathrm { {TH}}) as a function of charge on the floating gate quantum dots due to applied electrical stress. [ABSTRACT FROM AUTHOR]

The peculiarities of cross-gain modulation (XGM) in optically bistable quantum-dot vertical-cavity semiconductor optical amplifiers (QD-VCSOA) are theoretically studied. We find that the optical hysteresis can be controlled by XGM which for example can be utilized in resting an all-optical flip-flops using single QD-VCSOA. Our analysis reveals that intrinsic high-speed XGM response up to 200 GHz can be obtained in QD-VCSOA. [ABSTRACT FROM PUBLISHER]

We investigate the small-signal modulation response of two-section, gain-lever, quantum-dot semiconductor lasers. A three-pole modulation function is derived from a 3-D set of rate equations, and a 70% 3-dB bandwidth enhancement is computed and experimentally realized in an undoped quantum-dot gain-lever laser under extreme asymmetric-bias conditions. Finally, it is demonstrated that the 3-dB bandwidth is three times the free-running relaxation oscillation frequency in these types of laser structures, as opposed to 1.55 times in the case of conventional single-section lasers.