National Repository of Grey Literature 19 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Influence of Si doping in different layers on luminescence properties of InGaN/GaN multiple quantum well structure
Hájek, František ; Hospodková, Alice ; Oswald, Jiří ; Slavická Zíková, Markéta
Luminescence of InGaN/GaN multiple quantum well (MQW) structure is strongly affected by spontaneous and piezoelectric polarizations. To suppress them, doping with shallow impurities (e. g. Si) can be used. This works presents the effects of Si doping in different layers around the MQW area. On the basis of photoluminescence and cathodoluminescence measurements and band structure simulation, the piezoelectric field is most efficiently reduced when both layers under and over MQW area are Si doped.\n
Study of photocatalytic activity of Zn.sub.x./sub.Cd.sub.1-x./sub.S quantum dots in dependence on their composition using methylene blue
Praus, P. ; Svoboda, L. ; Hospodková, Alice ; Mamulová Kutláková, K.
ZnCdS quantum dots (QDs) with the different composition were prepared by precipitation of zinc and cadmium acetates with sodium sulphide in the presence of cetyltrimethylammonium bromide (CTAB) used for stabilization of their aqueous colloid dispersions. Transition energies of these quantum dots were determined from the UV-VIS spectra of QDs colloid dispersions and consequently used for calculation of the QDs sizes according to the Schrodinger equation. The ZnCdS QDs size was found to be significantly influenced by their composition: the QDs size decreased with the increasing Zn content. The photocatalytic activity of the ZnCdS QDs was studied using the methylene blue decomposition under UV irradiation. Different photocatalytic activity depending on the composition x was observed and explained. The maximal photocatalytic activity was achieved for x = 0.6 when the energy of the irradiation photons was still sufficient to generate electron-hole pairs in majority of the QDs and at the same time the photocatalytic surface area was maximal.\n
AlSb/InAsSb/AlSb deep QWs for the two band high temperature superlinear luminescence
Hulicius, Eduard ; Hospodková, Alice ; Pangrác, Jiří ; Mikhailova, M.
InAlAsSb/GaSb based hetero-nanostructures with deep quantum wells grown on GaSb are promising materials for the optoelectronic devices for near- and mid-IR spectral regions. Optical power and quantum efficiency of the LEDs based on the narrow bandgap semiconductor compounds (InGa)(AsSb) are limited by the nonradiative Auger recombination. Earlier we have proposed a method to increase the optical power in the bulk narrow bandgap and later in GaSb-based nanostructures with a deep QW by the effect of impact ionization on the QW with high band offset.
Characterisation of InAs/GaAs quantum dots by high resolution transmission electron microscopy
Zíková, Markéta ; Hospodková, Alice ; Pangrác, Jiří ; Hulicius, Eduard ; Komninou, Ph. ; Kioseoglou, J.
The InAs/GaAs quantum dots (QDs) covered by GaAsSb strain reducing layer (SRL) have suitable properties for various applications. The GaAsSb SRL covering InAs QDs is used to improve the structure growth and the final parameters like QD density, QD size or photoluminesence. To obtain high-quality structure with required properties, the structure growth and final structure have to be deeply studied. Since the QDs and SRL system is surrounded by GaAs, the high resolution transmission electron microscopy (HRTEM) measurement was used to reveal the real material arrangement in a prepared sample. In this work we will discuss the results of following HRTEM measurements: flatness and thickness of prepared layers, QD size, atomic arrangement and composition of GaAsSb layer.
Photocatalytic activity of ZnxCd.sub.1-x./sub.S quantum dots in dependence on their composition
Praus, P. ; Svoboda, L. ; Hospodková, Alice ; Mamulová-Kutláková, K.
ZnxCd1-xS quantum dots (QDs) with the different composition x were prepared by precipitation of Zn and Cd acetates with sodium sulphide from aqueous colloid dispersions. Transition energies of these QDs were determined from UV-VIS spectra of the QDs colloid dispersions and consequently used for calculation of the QDs sizes according to the Schrödinger equation. The ZnCdS QDs size was found to be significantly influenced by their composition, decreased with increasing the Zn content. The QDs were also characterized by TEM, X-ray powder diffraction and PL. The photocatalytic activity of the QDs was studied using the methylene blue decomposition under UV irradiation with the maximum intensity of 365 nm. Different photocatalytic activity depending on the composition x was observed. Quantum levels of the QDs have important influence on their photocatalytic activity as a result of quantum size effect. The maximal photocatalytic activity was achieved for x=0.6.
Luminescence of quantum dot heterostructures in applied electric field
Kubištová, Jana ; Zíková, Markéta ; Kuldová, Karla ; Pangrác, Jiří ; Hospodková, Alice ; Hulicius, Eduard ; Petříček, Otto ; Oswald, Jiří
In this work, photoluminescence (PL) and electroluminescence (EL) of samples with InAs/GaAs quantum dots were measured with electric voltage or current applied on the structure. The EL structures emitting at 1300 nm were prepared by using n-type substrate. By applying the electric voltage in reverse bias on the sample, the evinced PL may be switched off - it decreases rapidly with the applied voltage and is negligible at about 10 V. Such structures which PL intensity is tunable by applied voltage have a broad spectrum of applications in optoelectronics.
GaAsSb strain reducing layer covering InAs/GaAs quantum dots
Zíková, Markéta ; Hospodková, Alice ; Pangrác, Jiří ; Oswald, Jiří ; Kubištová, Jana ; Hulicius, Eduard ; Komninou, Ph. ; Kioseoglou, J. ; Nikitis, F.
GaAsSb is often used as a capping material for InAs quantum dots (QDs) due to its suitable conduction band alignment and suppression of In segregation from QDs during the capping process.We have found out that during the GaAsSb layer growth, Sb atoms segregate above InAs QDs, which is proved by the AFM and HRTEM measurements. For higher amount of Sb in GaAsSb, the measured photoluminescence (PL) has longer wavelength, but if it is too high, the structure may become type II with decreased PL intensity. For thick GaAsSb layer, the PL intensity decreases, because only big QDs participate to the PL.
In situ monitorování růstu MOVPE InAs/GaAs struktur s kvantovými tečkami pomocí reflektanční anisotropické
Vyskočil, Jan ; Hospodková, Alice ; Pangrác, Jiří ; Melichar, Karel ; Oswald, Jiří ; Kuldová, Karla ; Mates, Tomáš ; Šimeček, Tomislav ; Hulicius, Eduard
Reflectance anisotropy spectroscopy (RAS) has been used for the real-time observation and optimization of single and double InAs/GaAs quantum dot layer structure growth. The properties of samples were ex situ characterized by photoluminescence and AFM.
Lateral elongation of InAs/GaAs quantum dots studied by magnetophotoluminescence
Křápek, V. ; Kuldová, Karla ; Oswald, Jiří ; Hospodková, Alice ; Hulicius, Eduard ; Humlíček, J.
We have investigated single layer InAs QDs on GaAs substrate grown by MOVPE by means of magnetophotoluminescence up to 24 T. Fitting the field-dependence of band positions, we have found the ratio of lateral sizes within 1.5 –1.7, and the effective mass of 0.04 – 0.05.
Properties of InAs/GaAs quantum dots in vertically correlated structures with 2 QD layers grown by MOVPE
Vyskočil, Jan ; Hospodková, Alice ; Pangrác, Jiří ; Oswald, Jiří ; Mates, Tomáš ; Melichar, Karel ; Šimeček, Tomislav ; Hulicius, Eduard
We have studied the shape of QDs in structures with vertically correlated QDs where two layers of QDs were grown. We investigated the influence of spacer thickness on lateral shape (elongation) of QDs and photoluminescence intensity.

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