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Analysis of the training process Martin Jakš in the years 2010 - 2016
Franc, Jan ; Gnad, Tomáš (advisor) ; Jindra, Matouš (referee)
Title: The training process analysis of Martin Jakš in 2010 - 2016 Objectives: The purpose of this study is to pedagogically evaluate the training process of Martin Jakš, the member of the Czech cross-country skiing team. Methods: This study is designed as a case study. The study addresses a qualitative research, which was based on an analysis of training process of an elite cross-country skier. Training indicators and sport physical examination were analyzed and assessed with regard to racer's performance in the studied term. Results: The results of this study showed a tendency to decrease of athlete's performance in the studied term. Key terms: cross-country skiing, yearlong training cycle, training indicators, sport physical examination, performance
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Photoconductivity, photoluminescence and charge collection in semiinsulating CdTe and CdZnTe
Zázvorka, Jakub ; Franc, Jan (advisor) ; Humlíček, Josef (referee) ; Oswald, Jiří (referee)
Title: Photoconductivity, photoluminescence and charge collection in semiinsulating CdTe and CdZnTe Author: Jakub Zázvorka Department: Institute of Physics of Charles University Supervisor of the doctoral thesis: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles University. Abstract: Cadmium telluride and its compounds with zinc are the material of choice in spectroscopic room temperature high energy radiation detectors. The development of the final device is influenced by many parameters, including material impurities and defects, homogeneity and surface preparation. This thesis offers a comprehensive investigation of the detector fabrication process and of the parameters and physical effects influencing the spectroscopic resolution and performance of the detector. Structure of deep levels is investigated through photoluminescence and correlated with other electro-optical measurements dealing with the impact of structural imperfections of the material and their effect. The influence of resistivity and photoconductivity homogeneity on the detector performance is studied through electrical measurement of the charge carrier transport and charge collection of the sample. Obtained results are explained using the Fermi level shift theory and confronted with a theoretical model and calculations. The...
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Influence of Deep Levels on Charge Transport in CdTe and CdZnTe
Dědič, Václav ; Franc, Jan (advisor) ; Oswald, Jiří (referee) ; Štekl, Ivan (referee)
CdTe and CdZnTe are promising materials for room temperature semiconductor X-ray and gamma ray detectors. The accumulation of a space charge at deep energy levels due to a band bending at contacts with Schottky barriers and due to trapped photogenerated charge may result in time dependent change of charge collection efficiency in CdTe and CdZnTe detectors known as polarization effect. This thesis is mainly focused on a study of electric field profiles in detectors under dark and high photon flux conditions simulating detector operation using crossed polarizers technique exploiting the electro-optic (Pockels) effect. It also deals with a study of deep levels responsible for the polarization and influence of contact metals on charge accumulation. Several experimental results are supported by theoretical simulations. The measurements were performed on three sets of samples equipped with different contact metals (Au, In) cut from three different n-type CdTe and CdZnTe materials. Energy levels were detected using methods based on the Pockels effect and discharge current measurements. Detailed study of internal electric field profiles has revealed a fundamental influence of near midgap energy levels related to crystal defects and contact metals on the polarization in semiconductor detectors under high radiation...
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Studium elektrického pole v detektorech záření pomocí Pockelsova jevu
Hakl, Michael ; Franc, Jan (advisor) ; Richter, Ivan (referee)
Study of electric field in radiation detectors by Pockels effect (Master Thesis) by Michael Hakl Abstract Cadmium Telluride (CdTe) is a convenient candidate for room tem- perature detection of X-ray and gama radiation due to 1.5 eV band- gap energy and high atomic mass. Since CdTe has the highest linear electro-optical coefficient among II-VI compounds, the detector rep- resents a Pockels cell. Transmittance of the crystal is modulated by the internal electric field. Processing of infrared camera photographs results in an electric field profile between biasing electrodes. The elec- tric field in semi-insulting CdTe is influenced with deep level traps causing charge polarization under the electrodes. Occupation of traps is dependent on metal-semiconductor interface. Relation of charge accumulation and band bending for gold and indium contacts was studied. Repolarization/depolarization induced by additional illumi- nation with sub/above bandgap excitation laser was observed and ex- ploited for determination of the deep level energy. Results obtained by the Pockels-effect method were supported with luminescence measure- ments. Correlation between the occurrence of deep levels and surface point defects was discovered. Keywords: Pockels electro-optical effect, Cadmium Telluride ra- diation detector, Electric field, Schottky...
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The difference in load of the body between the rides on roller skis and cross-country skis.
Franc, Jan ; Gnad, Tomáš (advisor) ; Jindra, Matouš (referee)
Title: The difference in load of the body between the rides on roller skis and cross-country skis. Objectives: The aim of work is to determine the difference in load of the body between the rides on roller skis and ride on cross-country skis in skating and classic techniques. Methods: The work is conceived as a case study. It is a quantitative research carried out on the basis of comparing the values of heart rate and blood lactate concentration at one participant. The values were compared between the roller and cross-country skis when skating as well as classical techniques. Results: By the heart rate measuring and lactate concentration, the difference was detected between the roller and cross-country skis. We came to the result that the roller skis place less demands on the load of the body than cross- country skis which runners use to ski in winter. Keywords: cross-country skiing, cross-country skis, roller skis, lactate, heart rate
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Optical characterization of thin oxide layers
Statelov, Martin ; Franc, Jan (advisor) ; Moravec, Pavel (referee)
Performance of CdZnTe-based detectors is highly related to the surface quality. Mechanical polishing, chemical etching and passivation are routinely employed for this purpose. The dynamics and properties of CdZnTe surface oxide layers, created by etching-only and passivation by KOH and NH4F/H2O2 solutions, were studied by optical ellipsometry. Effective medium approximation model was used to evaluate ellipsometric spectra. Thickness and formation rate of the surface oxide layers differed in each of the passivation method. Leakage currents were measured simultaneously and were compared with the surface oxide layer properties. NH4F/H2O2 passivation showed to be method with most desirable properties of the surface oxide layer; thick oxide layer and low leakage currents.
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Influence of external fields on electric field and photocurrent in CdTe detectors
Rejhon, Martin ; Franc, Jan (advisor) ; Oswald, Jiří (referee)
This thesis is focused on a study of CdTe and CdZnTe semiconductor detectors working under high flux of radiation. We studied experimentally an influence of high flux of X-rays and optical radiation on polarization of the detector. The polarization phenomenon decreases the efficiency of the detector due to a screening of an applied electric field by a space charge accumulated at deep levels due to a trapping of photogenerated carriers. In order to measure the electric field profiles in the detectors we employed a method based on cross polarizers technique and Pockels effect. The main objective of this work was to study the possibilities of an optical de-polarization of CdTe and CdZnTe detectors for different photon energies of additional light, its dynamics and physical origin. We have found that detectors can be de-polarized by above bandgap light. Moreover, CdZnTe detector can be depolarized by near infrared light and in a pulse mode. The de- polarization is associated with a compensation of the space charge at deep traps.
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Electrooptic Pockels effect in X-ray radiation detectors
Rejhon, Martin ; Franc, Jan (advisor) ; Moravec, Pavel (referee)
In this work, we have added a temperature controller to an apparatus for measuring Pockels effect, which comprises of an integrated circuit and a Peltier element. Then the course of the electric field was measured in the sample of high resistance CdTe, a suitable detector on the high-energy radiation, depending on the voltage and temperature of the sample. Also the charge distribution in the sample was determined depending on time after the voltage and sample's temperature were reached. Finally, the activation energies of deep levels were determined, which are responsible for the polarization. Powered by TCPDF (www.tcpdf.org)
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Defects limiting charge collection in semiinsulated CdZnTe
Zajac, Vít ; Franc, Jan (advisor) ; Šikula, Josef (referee)
Title: Defects limiting charge collection in semiinsulated CdZnTe Author: Vít Zajac Department: Institute of Physics of Charles University Supervisor: doc. Ing. Jan Franc, DrSc., Institute of Physics of Charles University Abstract: We achieved to detect photoluminescence transitions deep in the band gap in 4 samples cut from 2 different crystals of semiinsulating Cd1-xZnxTe (x = 0,02 - 0,18) in a row of points along the growth axis. The spectral peaks give evidence of the presence of deep levels in the sample and the intensity of the photoluminescence peaks is to a certain extent proportional to the concentration of these levels. A comparison between resistivity and photoconductivity that were measured by a contact-less method showed that the change of photoluminescence intensity of deep levels does not bring about an unambigous change of neither resistivity nor photoconductivity. Correlation analysis of resistivity and photoconductivity of 6 samples from 4 different crystals confirmed the following model: A shift of the Fermi level within the band gap induced by a change of donor-acceptor compensation is accompanied by an unambigous change of resistivity and results in a change in occupation of the deep levels. This causes a change in the photoconductivity of the crystal because the occupation factor of...
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Photoelectric transport in high resistivity CdTe
Kubát, Jan ; Franc, Jan (advisor) ; Šikula, Josef (referee) ; Oswald, Jiří (referee)
Title: Photoelectric transport in high resistivity CdTe Author: Ing. RNDr. Jan Kubát Institute: Institute of Physics of Charles University Supervisor: Doc. Ing. Jan Franc, DrSc. Supervisor's e-mail address: jan.franc@mff.cuni.cz Abstract: CdTe is one of the most promising material for fabrication of X-ray and gamma ray detectors. Despite a considerable effort invested in material development there are still problems remain to be solved and influence efficiency of charge collection. We focus on study of polarization of the sample due to space charge accumulated on deep levels in this work. Samples of CdTe doped with Cl, Sn, In and Ge were investigated. Measurements of spectral dependence of photocurrent and lux- ampere characteristics were done. We performed mathematical modeling of measured data using an approach based on a three level compensation model, and solution of drift-diffusion and Poisson equations. Concentration of deep levels 1011 -1013 cm-3 was revealed in semiinsulating CdTe by modeling. Contact method measurement for determination of µτ product using I-A characteristics and Hecht relation was applied. Mapping of CdTe and CdZnTe samples via contact and contactless method was performed and measurements were compared. Correlation analysis of maps of electric resistivity and photoconductivity has...
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