National Repository of Grey Literature 5 records found  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.
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
Studie možnosti ovlivnění procesu transformace primární organické hmoty v kompostu ionty Ca+2 a Mg+2
HÁJEK, František
This study focuses on the entire proces of composting. It begins with listing the attributes of entry materials and spans to outlining the creation of characteristic substances in the compost (humus). Problems and solutions relating to determining the quality and quantity of humus in the compost are elaborated. This thesis was designed to identify efficient compost accelerator additives for gardening composts.
Compost accelerator to composters and garden composts
HÁJEK, František
The purpose of this paper is to research and suggest good-quality compost accelerators that could be effectively used in the garden composts. The additive eliminates the shortage of the input pulverized grass matter which is being composted. This thesis also describes the features of the compost, the nature of the correct composting procedures, and the legal implications to the production of the composting process. This paper elaborates the efficiency of the compost accelerators that are available within the home market and abroad. An important component of my accelerator is magnesium from the Dolomites limestone distributed by the "HASIT" company which positively affects the process of humification. The experiment of compostation with this type of accelerator took place on the pulverized grass matter. In order to objectively assess the quality of the composts, the Sanhoff´s method of stating the cation exchange capacity was used. During this experiment, the cation exchange capacity increased by 22% in the sample where the accelerator has been used, as compared to the sample where only the composted grass matter was present. Based on the results gathered, it is feasible to conclude that the suggested accelerator does have a significant impact on the composting of the grass matter. Due to this fact, it is strongly recommended to conduct a further research on the composition of the compost accelerators.

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