National Repository of Grey Literature 27 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
General overview of GaN devices and transport properties of AlGaN/GaN HEMT structures - impact of dislocation density and improved design
Hulicius, Eduard ; Hájek, František ; Hospodková, Alice ; Hubík, Pavel ; Gedeonová, Zuzana ; Hubáček, Tomáš ; Pangrác, Jiří ; Kuldová, Karla
GaN-based nanostructures are used for many present semiconductor devices. The main topics are structures for blue LEDs and LDs, but there are also other interesting and important GaN devices namely for power electronics, scintillators and detectors as well as High Electron Mobility Transistors (HEMT). Reduction of dislocation density considerably increases electron mobility in 2DEG. All presented results support our expectation that a suitably designed AlGaN back barrier can help to prevent this phenomenon.
Nanostructured layer enhancing light extraction from GaN-based scintillator using MOVPE
Vaněk, Tomáš ; Hubáček, Tomáš ; Hájek, František ; Dominec, Filip ; Pangrác, Jiří ; Kuldová, Karla ; Oswald, Jiří ; Hospodková, Alice
Light extraction (LE) efficiency of GaN buffer layer was studied by angle-resolved photoluminescence. We measured enhancement of light extraction efficiency (LEE) up to 154% by introducing the SiNx layer atop the GaN buffer and subsequent GaN light extraction layer (LEL) overgrowth. Morphological properties of GaN.
MOVPE GaN/AlGaN HEMT nano-structures
Hulicius, Eduard ; Kuldová, Karla ; Hospodková, Alice ; Pangrác, Jiří ; Dominec, Filip ; Humlíček, J. ; Pelant, Ivan ; Cibulka, Ondřej ; Herynková, Kateřina
GaN/AlGaN-based high electron mobility transistors (HEMTs) attain better performance than their state-of-the-art full silicon-based counterparts do, offering higher power, higher frequency as well as higher temperature of operation and stability, although their voltage and current limits are somewhat lower than for the SiC-based HEMTs. GaN/AlGaN-based HEMTs are a potential choice for electric-powered vehicles, for which they are approved not only for their power parameters, but also for their good temperature stability, lifetime and reliability. It is important to optimize HEMT structures and their growth parameters to reach the optimum function for the real-world applications. HEMT structures were grown by MOVPE technology in AIXTRON apparatus on (111)-oriented single-surface polished Si substrates. Structural, optical and transport properties of the structures were measured by X-ray diffraction, optical reflectivity, time-resolved photoluminescence and micro-Raman spectroscopy.\n
Datamining on publicly accessible data
Pangrác, Jiří ; Rauch, Jan (advisor) ; Chudán, David (referee)
This bachelor thesis deals with the datamining methods on publicly accessible data. Data mining is a technique of mining potentially interesting relations from data. Analysis is carried out on data provided by Česká obchodní inspekce, the czech office for trade inspection, which are accessible to public. I am trying to find possible answers for some analytical questions asked. For the analysis itself, LISp-Miner system was used focusing on 4ft-Miner and CF-Miner procedures. Besides the actual analysis, this thesis includes a brief description of LISp-Miner system and datamining generally. The main goal of this work is presentation of the results for their possible practical use.
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.
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.
Applications of porous III-V semiconductors in heteroepitaxial growth and in preparation of nanocomposite structures
Nohavica, Dušan ; Grym, Jan ; Gladkov, Petar ; Hulicius, Eduard ; Pangrác, Jiří
We investigate the concept of epitaxial growth on porous substrates Both crystalographically oriented and current line oriented pore networks in InP and GaAs were created by electrochemical dissolution. Heat treatment of InP pores at 650 ºC and GaAs pores at 700-850ºC converted them into microcavities. The capability of improved structural quality homo- and hetero-epitaxially overgrown films is demonstrated on InAs and GaInAs layers with a different composition grown on porous GaAs substrates
Nohavica, Dušan ; Grym, Jan ; Hulicius, Eduard ; Pangrác, Jiří ; Gladkov, Petar ; Jarchovský, Zdeněk
Structural and optical properties of micro and nano-porous InP and GaAs substrates used for an epitaxial overgrowth of thin films were investigated. Both crystalographically oriented (CO) and current line oriented (CLO) pore networks were created by electrochemical dissolution. Heat treatment of InP pores at 650oC and GaAs pores at 750-850oC converted them into microcavities The capability of improved structural quality homo- and hetero-epitaxially overgrown films on the porous InP, was also demonstrated by LPE growth of InP and InAs and GaInAs on GaAs by MOVPE technology.

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2 Pangrác, Jan
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