|
|
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.
|
|
|
EU and Terorism - Evolution of Common Policy 1999-2005
Hulicius, Eduard ; Šlosarčík, Ivo (advisor) ; Weiss, Tomáš (referee)
This thesis is dedicated to answer a question: How does the legislative and institutional answer of the EU on a challenge of new "superterrorism" look and are they different from traditional answers on "national terrorism"? The major problem of European anti-terrorism policy is the fact, that it is a relatively new issue. Efforts to organise on basis of existing integration a common coordinating policy in the 1970's and 1980's were only minor and unimportant. The impulse created in Maastricht Treaty on European union by establishing a pillar structure of the EU was important due to development of the third Pillar dedicated to Justice and Home affairs (JHA). Intergovernmental nature of this pillar has reduced possibilities of the central institutions to influence creation of the new policies. However, a new agency - EUROPOL. European police agency was to be established thanks to the Treaty. Combat with terrorism was only one of many targets of the newly created JHA policies throughout 1990's. Action Plan on JHA from Tampere (1999) focused primarily on migration issues. The EU is focusing on a multi- forged strategy to deal with terrorism. In comparison to example of the USA is the main focus of the E U laid on internal policies. The EU position can be described as responsive - although the latest development...
|
|
|
Structural defects in II-VI semiconductors
Šedivý, Lukáš ; Belas, Eduard (advisor) ; Hulicius, Eduard (referee) ; Schneeweiss, Oldřich (referee)
Title: Structural defects in II-VI semiconductors Author: Lukáš Šedivý Department: Institute of Physics of Charles University Supervisor: Doc. Ing. Eduard Belas, CSc., Institute of Physics, Faculty of Mathematics and Physics, Charles University Abstract: The single crystalline CdTe doped by chlorine is an excellent material for man- ufacturing x-ray and gamma-ray room-temperature semiconductor detectors thanks to the large linear attenuation coefficient, the possibility to make it high-resistive at the room temperature, and good electron mobility and the lifetime. This thesis aimed to examine the effect of annealing in well-defined ambient component pressure, Cd or Te, on the crys- tal's defect structure. The first experimental is devoted to eliminating the second phase defects - inclusions - present in CdTe : Cl, which significantly decay the crystal quality and detection performance. The following experimental parts are focused on the detailed inves- tigation of the point defect structure of CdTe : Cl. The annealing interval bisection method for reaching high resistivity material is introduced. The equilibrium defect structure is in- vestigated using the in-situ high-temperature Hall effect measurements. The results are interpreted through an advanced model of the defect structure considering also dissocia-...
|
|
|
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
|
|
|
EU and Terorism - Evolution of Common Policy 1999-2005
Hulicius, Eduard ; Šlosarčík, Ivo (advisor) ; Weiss, Tomáš (referee)
This thesis is dedicated to answer a question: How does the legislative and institutional answer of the EU on a challenge of new "superterrorism" look and are they different from traditional answers on "national terrorism"? The major problem of European anti-terrorism policy is the fact, that it is a relatively new issue. Efforts to organise on basis of existing integration a common coordinating policy in the 1970's and 1980's were only minor and unimportant. The impulse created in Maastricht Treaty on European union by establishing a pillar structure of the EU was important due to development of the third Pillar dedicated to Justice and Home affairs (JHA). Intergovernmental nature of this pillar has reduced possibilities of the central institutions to influence creation of the new policies. However, a new agency - EUROPOL. European police agency was to be established thanks to the Treaty. Combat with terrorism was only one of many targets of the newly created JHA policies throughout 1990's. Action Plan on JHA from Tampere (1999) focused primarily on migration issues. The EU is focusing on a multi- forged strategy to deal with terrorism. In comparison to example of the USA is the main focus of the E U laid on internal policies. The EU position can be described as responsive - although the latest development...
|
|
| |
|
|
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.
|
|
|
Preparation and characterization of selected optical materials
Hulicius, Eduard
Crystal structure and technology procedure was optimized to obtained better parameters of PL and RL as well as homogeneity of structure. Structural and optical parameters were measured and evaluated; their influence on crystal characteristics was discussed. New improved material was proposed. P.W = Peak wavelength; P.I = Peak intensity; FWHM = Full With in Half Maximum; D.W = dominant wavelength; I.W = integral w.; I.I = integrated intensity; R.F = reflectivity; T.H = thickness were measured.
|
|
|
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.
|
guest ::
