Point defects in materials for detection of X-ray and gamma radiation
Author: RNDr. Martin Rejhon, PhDSupervisor: Prof. Ing. Jan Franc, DrSc.
Consultants: RNDr. Václav Dědič, PhD., doc. RNDr. Jan Kunc, PhD.
Type: Doctoral
Abstract: Cadmium telluride and its compounds are suitable materials for production of X-ray and gamma-ray detectors working at room temperature. However, the detector quality is affected by material imperfections, such as crystal defects and impurities. It results into forming of deep levels which act as recombination 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 methods with focus on differences between CdTe, CdZnTe, CdTeSe and CdZnTeSe. The electro-optic Pockels effect is used to investigate the influence of the illumination 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 responsible for space charge dynamics. Several numerical simulations based on solution of the drift-diffusion and Poisson equations, including the Shockley-Read-Hall model are performed in order to confirm our conclusions.
Keywords: Electro-optic Pockels effect, X-ray and gamma-ray detector, CdTe, deep levelsDownload: Point defects in materials for detection of X-ray and gamma radiation