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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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Point defects in materials for detection of X-ray and gamma radiation
Rejhon, Martin ; Franc, Jan (advisor) ; Oswald, Jiří (referee) ; Toušek, Jiří (referee)
Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...
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Influence of external fields on electric field and photocurrent in CdTe detectors
Rejhon, Martin ; Franc, Jan (advisor)
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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Point defects in materials for detection of X-ray and gamma radiation
Rejhon, Martin ; Franc, Jan (advisor) ; Oswald, Jiří (referee) ; Toušek, Jiří (referee)
Title: Point defects in materials for detection of X-ray and gamma radiation Author: Martin Rejhon Department: Institute of Physics of Charles University Supervisor: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles Uni- versity Abstract: Cadmium telluride and its compounds are suitable materials for pro- duction of X-ray and gamma-ray detectors working at room temperature. How- ever, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as re- combination and trapping centers. Then, the accumulated space charge at these deep levels influences electric and spectroscopic properties of the detector. In the end it may result in the polarization effect, when the electric field is localized in vicinity of one contact and detection properties are decreased. This thesis reports a complex study of a detector band structure by various meth- ods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumi- nation in range 900 − 1800 nm on the inner electric field. The temperature and time evolutions of the electric field after application of bias or switching of the additional light at 940 nm were measured to determine deep levels...
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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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Influence of external fields on electric field and photocurrent in CdTe detectors
Rejhon, Martin ; Franc, Jan (advisor)
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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Hodnocení pracovního výkonu ve Škoda Auto a Energetickém regulačním úřadu
Broulík, Jan ; Šikýř, Martin (advisor) ; Rejhon, Martin (referee)
Práce porovnává systémy hodnocení pracovního výkonu ve Škoda Auto a Energetickém regulačním úřadu z hlediska příslušnosti těchto organizací k soukromému a veřejnému sektoru. V teoretické části pojednává o řízení a hodnocení pracovního výkonu. Praktická část analyzuje systémy hodnocení pracovního výkonu ve zkoumaných subjektech. Autor dochází k závěru, že rozdílnost cílů veřejného a soukromého sektoru nemusí nutně vést k rozdílům v systému hodnocení pracovního výkonu.
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