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Charge transport in semiconducting radiation detectors
Pipek, Jindřich ; Belas, Eduard (advisor)
This thesis is focused on study of charge transport in semiconducting radiation detectors. Theoretical calculations of current waveforms based on continuity equation and drift-diffusion equation are done. Useful approximations of current waveforms for detector with shallow electron trap are discussed. Monte Carlo simulation of the current waveforms is proposed and applied to fit experimental current waveforms measured using laser-induced transient current technique and for evaluation of charge transport parameters of the detector such as electric field profile, trapping and detrapping time of traps, drift mobility and other parameters. Detectors prepared from semi-insulating GaAs and CdZnTe single crystals are tested using electrical, spectroscopic and optical characterization techniques.
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Effect of the laser pulse illumination on charge collection efficiency in radiation detectors.
Betušiak, Marián ; Belas, Eduard (advisor) ; Oswald, Jiří (referee)
The main focus of this thesis is the characterization of the charge transport in CdZnTe radiation detectors and the study of the effect of the detector illumination on charge transport. The transport properties are evaluated using Laser-induced Transient Current Technique and the Monte Carlo simulation is used for fitting the measured current waveforms. The properties of the detector prepared from semi-insulating CdZnTe single crystal with a platinum Schottky contacts were measured in the dark in the unpolarized and polarized state and under the anode and cathode continuous LED above-bandgap illumination.
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Electrical and optical properties of SiC single crystals
Brynza, Mykola ; Belas, Eduard (advisor) ; Štekl, Ivan (referee)
Silicon carbide is a semiconductor with a wide bandgap of up to 3.2 eV and is capable of operating in extreme conditions, high temperature and high energy modes. This work focuses on the investigation of electrical and optical properties of monocrystalline SiC by various methods including Raman spectroscopy, volt-ampere characteristics, L-TCT and spectroscopic techniques. The adhesion of contacts and the influence of different contact materials on the ability to detect ionizing radiation are also studied to optimize the technology of preparation of quality SiC-based radiation detectors.
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Spectral dependency of the charge generation in semiconductor detectors using nano-second laser pulses
Raja, Marek ; Belas, Eduard (advisor) ; Franc, Jan (referee)
This work deals with the study of charge transport in a semiconductor detector made of CdZnTe material. Theoretical models of charge density distribution are based on a drift-diffusion equation with consideration of infinite and finite lifetime of a charge carrier caused by a shallow and deep trap. The shapes of the measured waveforms with the L-TCT method are fitted by the Monte Carlo method. The obtained values of drift mobility, electric field profile, charge passage time and surface recombination rate are obtained by fitting with the OriginPro program.
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Structure defects in SiC radiation detectors
Zetek, Matyáš ; Belas, Eduard (advisor)
Silicon carbide (SiC), is a wide band gap (2.4 eV < Eg < 3.3 eV) semiconducting material well known for its potential applications in high-temperature, high-power, high-frequency or hard radiation resistant devices. In this thesis, we are broadening elementary knowledge about this material. We identify energy levels in the material, using Photo-Hall effect spectroscopy supported by the temperature dependency of classic Hall effect measurement and temperature dependent photoluminescence. This knowledge is essential to allow SiC application as a radiation detector.
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Structure defects in SiC radiation detectors
Zetek, Matyáš ; Belas, Eduard (advisor) ; Hazdra, Pavel (referee)
Silicon carbide (SiC), is a wide band gap (2.4 eV < Eg < 3.3 eV) semiconducting material well known for its potential applications in high-temperature, high-power, high-frequency or hard radiation resistant devices. In this thesis, we are broadening elementary knowledge about this material. We identify energy levels in the material, using Photo-Hall effect spectroscopy supported by the temperature dependency of classic Hall effect measurement and temperature dependent photoluminescence. This knowledge is essential to allow SiC application as a radiation detector.
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Charge transport in semiconducting radiation detectors
Pipek, Jindřich ; Belas, Eduard (advisor) ; Hazdra, Pavel (referee)
This thesis is focused on study of charge transport in semiconducting radiation detectors. Theoretical calculations of current waveforms based on continuity equation and drift-diffusion equation are done. Useful approximations of current waveforms for detector with shallow electron trap are discussed. Monte Carlo simulation of the current waveforms is proposed and applied to fit experimental current waveforms measured using laser-induced transient current technique and for evaluation of charge transport parameters of the detector such as electric field profile, trapping and detrapping time of traps, drift mobility and other parameters. Detectors prepared from semi-insulating GaAs and CdZnTe single crystals are tested using electrical, spectroscopic and optical characterization techniques.
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Charge transport optical characterization in semiconductor radiation detectors
Ridzoňová, Katarína ; Belas, Eduard (advisor)
Measurements of DC photocurrent-voltage characteristic, photocurrents spectral response and laser induced transient current technique enable investigation of surface recombination centers, bulk trap levels and distribution of the inner electric field. In the presented work, the n- type planar CdZnTe detectors with quasi Ohmic contacts were studied by above mentioned methods. It has been shown that in the case of strongly absorbed light under the DC regime of illumination not only surface recombination influences the detector's transport properties. The effect of the space charge, created as a consequence of carriers trapped by the impurity levels, must be taken into account. Therefore some new theoretical models were created in order to describe measured photocurrent-voltage dependencies. Obtained data were fitted with the new theory and the mobility and surface recombination velocity for electrons were determined.
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Room-temperature semiconducting detectors
Pekárek, Jakub ; Belas, Eduard (advisor) ; Oswald, Jiří (referee) ; Štekl, Ivan (referee)
Semiconducting material CdTe/CdZnTe has a huge application potential in spectroscopic room temperature radiation detection due to its properties. Such detectors can be used in medical applications, homeland security and for monitoring of nuclear facilities. However, the final device quality is influenced by many parameters. One crucial stage in detector fabrication is the proper surface treatment. The detailed study of surface treatments and their effect on final detector device is reported. Another crucial fact is the polarization of the detector caused by high radiation fluxes which negatively affects the use of such devices. The polarization occurs by capturing the photogenerated holes at the deep levels inside the semiconductor. The possible detector depolarization by infrared illumination during the detector operation has been experimentally verified and the obtained results are shown in this thesis. For optimal technology of preparation, it is also necessary to develop the fast characterization method for prepared detectors. The last aim of the thesis is to study the resulting quality of prepared planar and co-planar detectors by transient-current-technique (TCT). TCT is an electro-optical method allowing to determine variety of transport properties of radiation detectors, such as internal electric...
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Study of the charge collection efficiency affected by metalization in Gamma and X- ray detectors
Pipek, Jindřich ; Belas, Eduard (advisor) ; Grill, Roman (referee)
In this thesis, the influence of metal contacts, prepared on CdZnTe-based semiconductor material by electroless deposition using aqueous or alcohol based solution, on the detection quality of Gamma and X-ray detectors. The quality of metal contacts is also affected by surface treatments. From single crystal of CdZnTe the testing detector was made. Electrical, spectroscopic and optical characterization techniques were used and their results were compared for two mentioned types of contacts. The aim was to show the possibility of preparing high quality metal contacts prepared from alcohol based solution of Gold(III) chloride. Alcohol based contacts are new method for preparing chemical contacts and promise different properties from standard chemical contacts prepared from aqueous based solution of Gold(III) chloride.
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