Papers by Keyword: Quantum Dot

Abstract: Improving the efficiency of greenhouses is one of the most promising directions in development of agriculture. New perspectives in this field opened up with the development of the new methods of synthesis of a new generation of photoluminescent materials based on colloidal semiconductor photoluminophores (so-called "quantum dots"). It is shown that use of the covering materials containing quantum dots can significantly increase yields. Moreover, introduction of these quantum dots into commercial production can significantly improve the mechanical properties of the covering films used for greenhouses and slow down the process of their destruction. The durability of greenhouse films increases from 1 to 3 years.

Abstract: Indium phosphide (InP) quantum dots (QDs) with luminescence tunable over the entire visible spectrum were prepared by the conventional hot injection method. InP QDs are considered alternatives to Cadmium containing QDs for application in light-emitting devices because of showing similar optical properties to those containing toxic heavy metals. The multishell coating was shown to improve the photoluminescence quantum yield (QY) of InP QDs more strongly than the conventional ZnS shell coating. QY values were more than 60% along with FWHM of 41-73 nm can be routinely achieved, making the optical performance of InP/ZnS/ZnS or InP/ZnS/SiO₂ QDs comparable to that of InP/ZnS QDs. These QDs and the polymer dissolved in the appropriate solvent and deposited by casting to give homogeneous films and showed a good level of dispersion of the QDs within the polymer.

Abstract: We analyze the bistable characteristics of quantum dot vertical cavity semiconductor optical amplifier integrated with saturable absorber. The device demonstrates bistable characteristics in the input-output powers which can be controlled by changing the voltage of the saturable absorber. We observe that the lower trigger level is more sensitive to variation of the absorption coefficient of the saturable absorber than that of upper trigger level. For clockwise and butterfly loops, we find that the upper and lower trigger levels increase as the absorption coefficient increases, and consequently the hysteresis width decreases. For counter clockwise, the upper and lower trigger levels decrease as the absorption coefficient increases and the corresponding hysteresis width increases.

Abstract: This paper presents the improvement of intrinsic carrier concentrations in the active layer of solar cell structure using Indium Nitride quantum dot as the active layer material. We have analyzed effective density of states in conduction band and valance band of the solar cell numerically using Si, Ge and InN quantum dot in the active layer of the solar cell structure in order to improve the intrinsic carrier concentration within the active layer of the solar cell. Then obtained numerical results were compared. From the comparison results it has been revealed that the application of InN quantum dot in the active layer of the device structure improves the effective density of states both in conduction band and in the valance band. Consiquently the intrinsic carrier concentration has been improved significently by using InN quantum dot in the solart cell structure.

Abstract: In silicon nanoscale transistors, dopant (impurity) atoms can significantly affect transport characteristics, in particular at low temperatures. Coupling of neighboring dopants in such devices is essential in defining the properties for transport. In this work, we briefly present a comparison of different regimes of inter-dopant coupling, controlled by doping concentration and, to some extent, by selective, local doping. Tunneling-transport spectroscopy can reveal the energy spectrum of isolated dopants and of strongly-coupled dopant atoms. Interactions of multiple-dopants quantum dots (QDs) and satellite individual dopant-traps, as observed in some devices, can provide further information to bridge such inter-dopant coupling regimes for more advanced applications.

Abstract: TiO₂ nanocrystalline semiconductor film was made on the titanium (Ti) substrate by hydrothermal method,and then prepared the CdSe quantum dot layer on the face of the TiO₂ nanocrystalline semiconductor film by electrochemical deposition method. We studied the affect of deposition voltage of the CdSe quantum dots’ growth, finding that when the deposition voltage was-1.3V,CdSe quantum dots grown best.However, In terms of CdSe/TiO₂ as the light-anode,using electricity chemistry workstation to test,We gain a solar cell with Short circuit current density of 1.45×10^-3A·cm^-2 and the open circuit voltage of 0.24 V.

Abstract: A one-pot synthetic method for non-toxic Ni₃S₂ quantum dots (QDs) was proposed by using commercial available nickel acetate as the precursor. The obtained quantum dots were characterized by photoluminescence spectroscopic, powder X-ray diffraction, and transmission electron microscopy. The maximum fluorescence emission peak of Ni₃N₂ QDs is at 469 nm under the 365 nm ultraviolet light irradiation in PL Spectra. The TEM data reveals that the predominance of particles with a polyhedron structure and the range of average particle size are between 5 and 11 nm.

Abstract: A novel one pot synthesis approach in oleic acid medium was employed to obtain monophasic ZnSe quantum dots (QD) of average size 3.7nm. The QDs were well crystalline in hexagonal phase as revealed by x-ray diffraction and high resolution transmission electron microscopy (HRTEM) studies. The ZnSe QDs exhibit sharp emission peak in the blue (465nm) with 385picosecond fluorescence decay time. The theoretical band gap corresponding to 3.7nm ZnSe QDs matched well with the measured 3.11eV band gap of synthesized QDs which thus showed quantum confinement effect.

Abstract: In the present work the possibility of simultaneous localization of two electrons in Δ¹⁰⁰ and Δ⁰⁰¹ valleys in ordered structures with Ge/Si quantum dots (QD) was verified experimentally by electron spin resonance (ESR) method. ESR spectra obtained for the ordered ten-layered QD structure in the dark shows the signal corresponding to electron localization in Si at the Ge QD base edges, in Δ¹⁰⁰, Δ⁰¹⁰ valleys (g_zz=1.9985, g_in-plane=1.999). Light illumination causes the appearance of a new ESR line (g_zz=1.999) attributed to the electrons in Δ⁰⁰¹ valley localized at the QD apexes. Observed effect is explained by enhancement of electron confienment near QD apex by Coloumb attraction to the photogenerated hole trapped in Ge QD.

Abstract: Structural investigations of Si quantum dots (QDs) grown by CVD on two different heterostructures: AlN/Si (111) and 3C-SiC/Si (100) are conducted. The Si QDs have been grown using silane as precursor, diluted in hydrogen, at fixed temperature and pressure (830°C - 800mbar). High densities of dots can be obtained (up to 10¹¹ cm^-2) with typical heights below 10nm. The kinetic of deposition lets suppose the presence of an initial wetting layer before the dots formation. Different durations are required for nucleating dots on AlN and 3C-SiC. Si QDs on AlN present a luminescence band which can be attributed to quantum confinement.