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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 Deep Levels on Charge Transport in CdTe and CdZnTe
Dědič, Václav
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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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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Measurement of the electric field in semiconductor detector with non-trivial contact geometry
Fridrišek, Tomáš ; Dědič, Václav (advisor) ; Trojánek, František (referee)
The main aim of this bachelor thesis was to investigate whether it is possible to use a new method based on the electro-optical Pockels effect, to study the internal electric field in the coplanar grid detector. The Pocklels coefficient for CdZnTe was determined by measuring the detector with trivial contact geometry. Subsequently, the found Pockels coefficient was used for evaluation of 2D vector field for samples with non-trivial contact geometry. This method was successful to evaluate the electric field in almost entire volume in coplanar grid detectors.
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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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Influence of Deep Levels on Charge Transport in CdTe and CdZnTe
Dědič, Václav
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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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)
|
|
|
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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