We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the ...optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.
We report room-temperature Raman scattering studies of nominally undoped (100) GaAs1−xBix epitaxial layers exhibiting Bi-induced (p-type) longitudinal-optical-plasmon-coupled (LOPC) modes for 0.018 ≤ ...x ≤ 0.048. Redshifts in the GaAs-like optical modes due to alloying are evaluated and are paralleled by strong damping of the LOPC. The relative integrated Raman intensities of LO(Γ) and LOPC ALO/ALOPC are characteristic of heavily doped p-GaAs, with a remarkable near total screening of the LO(Γ) phonon (ALO/ALOPC → 0) for larger Bi concentrations. A method of spectral analysis is set out which yields estimates of hole concentrations in excess of 5×1017cm−3 and correlates with the Bi molar fraction. These findings are in general agreement with recent electrical transport measurements performed on the alloy, and while the absolute size of the hole concentrations differ, likely origins for the discrepancy are discussed. We conclude that the damped LO-phonon-hole-plasmon coupling phenomena plays a dominant role in Raman scattering from unpassivated nominally undoped GaAsBi.
A high-performance 1.3 μm InAs/GaAs quantum-dot laser directly grown on Si substrates has been achieved by using InAlAs/GaAs strained-layer superlattice serving as dislocation filter layers (DFLs). ...The Si-based laser achieves lasing operation up to 111°C with a threshold current density of 200 A/cm2 and an output power exceeding 100 mW at room temperature.
We studied the growth of InAs/InGaP quantum dot (QD) solar cells with near ideal bandgaps for intermediate band solar cells. Using a solid-source molecular beam epitaxy system, the evolution of InAs ...QDs grown on an InGaP buffer layer was examined as a function of InAs coverage and growth temperature. QDs were initiated with defective clusters for InAs deposition as small as 0.3 monolayer. The cross diffusion of In atoms and As–P exchange between InAs and the InGaP buffer layer could be responsible for the formation of coherent QDs and large defective clusters. An AlGaAs interlayer was inserted between InAs and the InGaP buffer layer to prevent the surface exchange reactions between InAs and InGaP. As a result, InAs QDs with a density of 1×1011cm−2 have been demonstrated with stronger photoluminescence emission compared to those with the GaAs interlayer. This growth technique was applied to fabricate InAs/InGaP QD solar cells. Post-growth annealing treatment was also investigated to improve the performance of QD solar cells.
•We studied the growth of InAs quantum dots on InGaP surface.•We have used AlGaAs interlayer to improve the quality of the quantum dots.•Rapid thermal annealing was applied to the fabricated quantum dot solar cells.•Optical tests reveal good quality of the InAs/InGaP solar cell.
We report the growth of InAs(1-x)Sb(x) self-assembled quantum dots (QDs) on GaAs (100) by molecular beam epitaxy. The optical properties of the QDs are investigated by photoluminescence (PL) and ...time-resolved photoluminescence (TRPL). A type I to type II band alignment transition is demonstrated by both power-dependent PL and TRPL in InAs(1-x)Sb(x) QD samples with increased Sb beam flux. Results are compared to an eight-band strain-dependent k x p model incorporating detailed QD structure and alloy composition. The calculations show that the conduction band offset of InAs(1-x)Sb(x)/GaAs can be continuously tuned from 0 to 500 meV and a flat conduction band alignment exists when 60% Sb is incorporated into the QDs. Our study offers the possibility of tailoring the band structure of GaAs based InAsSb QDs and opens up new means for device applications.
The structures of 5,7-di(
tert
-butyl)-2-(5,8-dimethyl-4-piperidinoquinolin-2-yl)-3-hydroxytropone, 5,7-di(
tert
-butyl)-3-chloro-2-(5,8-dimethyl-4-piperidinoquinolin-2-yl)tropone, 5,7-di(
tert
...-butyl)- 3-(3,5-dimethylphenylamino)-2-(5,8-dimethyl-4-piperidinoquinolin-2-yl)tropone, and 3-(
N
-acetyl-3,5- dimethylphenylamino)-5,7-di(
tert
-butyl)-2-(5,8-dimethyl-4-piperidinoquinolin-2-yl)tropone were determined by X-ray diffraction. These compounds were synthesized through a series of transformations, including the nucleophilic substitution of the chlorine atom by piperidine in the starting 5,7-di(
tert
-butyl)-2-(4- chloroquinolin-2-yl)-3-hydroxytropone followed by the three-step functionalization of the 3-position in 3-hydroxytropone. The nature of dynamic processes in a solution of
N
-acetyl-3-arylaminotropone associated with the rotation of the
N
-acetyl group was revealed by the PCM/PBE0/6-31G(
d,p
) method.
•Multilayered InGaAs/GaAs QD structures were grown using As2 flux.•Three-dimensional ordering of self-assembled QD arrays was observed.•Nanostructures were studied by TEM, AFM, and ...photoluminescence.•Observed regularities were explained by competing diffusion and strain on surface.•3D ordering of QDs can be controlled by growth temperature.
A comprehensive microscopy analysis has been undertaken to study three-dimensional quantum dot (QD) ordering in multilayered In0.4Ga0.6As/GaAs structures grown with an As2 flux at different substrate temperatures. Atomic force microscopy, transmission electron microscopy, and photoluminescence measurements were employed to fully understand the formation of these extended dot structures. Changes in the lateral pattern of QD ordering are correlated with their vertical alignment. These correlations are analyzed in light of the inherent transformation of the wetting and spacer layers, as well as changes in the shape, strain, and composition of individual QDs. The experimental results are attributed to the anisotropy in the thermally activated surface mass transport and the relaxation of elastic stresses.
The reaction of 4-chloro-2,7,8-trimethylquinoline with 4,6-di(
tert
-butyl)-3-(piperidin- 1-ylmethyl)-1,2-benzoquinone, which was prepared by the
in situ
oxidation of 4,6-di(
tert
- ...butyl)-3-(piperidin-1-ylmethyl)pyrocatechol with sodium nitrite, gave 4,6-di(
tert
-butyl)-2- (4-chloro-7,8-dimethylquinolin-2-yl)-7-(piperidin-1-ylmethyl)-1,3-tropolone. Its structure was determined by X-ray diffraction. The energy and structural characteristics of the tauto- mers of this compound in the gas phase and in a polar solution were calculated by quantum chemical methods (PBE0/6-311+G(d,p)).
A synthetic procedure towards 4,6-diisopropyl-3-nitro-1,2-benzoquinone was elaborated. Based on this benzoquinone, a series of novel 5,7-diisopropyl-2-(quinolin-2-yl)-1,3-tropolones and ...5,7diisopropyl-2-(quinolin-2-yl)-4-nitro-1,3-tropolones were derived. Molecular structure of 2-(4-chloro-8-methylquinolin-2-yl)-5,7-diisopropyl-1,3-tropolone was established by X-ray diffraction analysis. Energetic and structural characteristics of isomeric 5,7-diisopropyl-2-(quinolin-2yl)-1,3-tropolones and 5,7-diisopropyl-2-(quinolin-2-yl)-4-nitro-1,3-tropolones in the gas phase and in the polar solvent were calculated by quantum chemistry method (PBE0/6-311+G(d,p)).
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