Transport náboje v polovodičích

Tato práce je zaměřena na studium transportu náboje v polovodičích. Simulace Monte Carlo je propojena s numerickým řešením drift-difuzní rovnice a Poissonovy rovnice. Tyto numerické simulace transportu náboje jsou aplikovány na experimentální data s cílem získat parametry transportu náboje v detektoru, jako je profil elektrického pole, hustota prostorového náboje, energie, záchytný průřez a koncentrace hladin defektů, driftová pohyblivost a difúzní koeficient nosičů náboje a další transportní parametry. Polovodičové vzorky připravené ze semiizolačních monokrystalů GaAs, CdZnTe a CdZnTeSe jsou studovány pomocí elektrických, spektroskopických a optických charakterizačních technik.This thesis is focused on the study of charge transport in semiconductors. Monte Carlo simulation is combined with the numerical solution of the coupled drift-diffusion equation with Poisson's equation. These numerical simulations of charge transport are applied to experimental data to obtain charge transport parameters of the detector, such as electric field profile, space charge density, defect level energy, capture cross section and concentration, charge carrier drift mobility and diffusion coefficient, and other parameters. Semiconductor samples prepared from semi-insulating GaAs, CdZnTe, and CdZnTeSe single crystals are studied using electrical, spectroscopic, and optical characterization techniques.Fyzikální ústav UKInstitute of Physics of Charles UniversityMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Transport náboje v polovodičových detektorech záření

Tato práce se zaměřuje na studium transportu náboje v polovodičových detektorech záření. Jsou provedeny teoretické výpočty proudových závislostí založené na rovnici kontinuity a drift-difúzní rovnici. Užitečné aproximace proudových závislostí pro detektor s mělkou elektronovou pastí jsou diskutovány. Monte Carlo simulace proudových závislostí je navržena a aplikována na experimentální proudové závislosti změřené pomocí laserem indukované metody tranzientních proudů pro získání transportních parametrů náboje v detektoru jako je profil elektrického pole, driftová pohyblivost a další parametry. Detektory vyrobené z vysoko odporových GaAs a CdZnTe monokrystalů jsou testovány pomocí elektrických, spektroskopických a optických charakterizačních metod.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.Fyzikální ústav UKInstitute of Physics of Charles UniversityFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Transport náboje v polovodičových detektorech záření

Tato práce se zaměřuje na studium transportu náboje v polovodičových detektorech záření. Jsou provedeny teoretické výpočty proudových závislostí založené na rovnici kontinuity a drift-difúzní rovnici. Užitečné aproximace proudových závislostí pro detektor s mělkou elektronovou pastí jsou diskutovány. Monte Carlo simulace proudových závislostí je navržena a aplikována na experimentální proudové závislosti změřené pomocí laserem indukované metody tranzientních proudů pro získání transportních parametrů náboje v detektoru jako je profil elektrického pole, driftová pohyblivost a další parametry. Detektory vyrobené z vysoko odporových GaAs a CdZnTe monokrystalů jsou testovány pomocí elektrických, spektroskopických a optických charakterizačních metod.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.Fyzikální ústav UKInstitute of Physics of Charles UniversityFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI(3), giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes

Charge transport in semiconducting radiation detectors

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

Charge transport in semiconducting radiation detectors

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

Charge transport in semiconductors

This thesis is focused on the study of charge transport in semiconductors. Monte Carlo simulation is combined with the numerical solution of the coupled drift-diffusion equation with Poisson's equation. These numerical simulations of charge transport are applied to experimental data to obtain charge transport parameters of the detector, such as electric field profile, space charge density, defect level energy, capture cross section and concentration, charge carrier drift mobility and diffusion coefficient, and other parameters. Semiconductor samples prepared from semi-insulating GaAs, CdZnTe, and CdZnTeSe single crystals are studied using electrical, spectroscopic, and optical characterization techniques

Study of the charge collection efficiency affected by metalization in Gamma and X- ray detectors

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

Charge transport in semiconducting radiation detectors

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

Modelling Polarization Effects in a CdZnTe Sensor at Low Bias

Semi-insulating CdTe and CdZnTe crystals fabricated into pixelated sensors and integrated into radiation detection modules have demonstrated a remarkable ability to operate under rapidly changing X-ray irradiation environments. Such challenging conditions are required by all photon-counting-based applications, including medical computed tomography (CT), airport scanners, and non-destructive testing (NDT). Although, maximum flux rates and operating conditions differ in each case. In this paper, we investigated the possibility of using the detector under high-flux X-ray irradiation with a low electric field satisfactory for maintaining good counting operation. We numerically simulated electric field profiles visualized via Pockels effect measurement in a detector affected by high-flux polarization. Solving coupled drift–diffusion and Poisson’s equations, we defined the defect model, consistently depicting polarization. Subsequently, we simulated the charge transport and evaluated the collected charge, including the construction of an X-ray spectrum on a commercial 2-mm-thick pixelated CdZnTe detector with 330 µm pixel pitch used in spectral CT applications. We analyzed the effect of allied electronics on the quality of the spectrum and suggested setup optimization to improve the shape of the spectrum