Design Of CdZnTe Particle Detector And Irradiation Damage On Its Performance

The radiation detector is an indispensable instrument in particle physics research,nuclear physics research,and nuclear radiation application.It has been widely used in space physics,nuclear power,geological exploration,medical treatment,epidemic prevention,food inspection,agriculture,and other fields.In recent years,ternary compound semiconductor CdZnTe detectors received considerable attention for radiation detection.The radiation category encountered in experimental nuclear physics and nuclear technology application is complex in most cases.More stringent requirements have been put forward for the detection of different kinds of radiation,identification of radiation particles and anti-irradiation properties.This work mainly focuses on the influence factors of neutron and charged particle detection of CdZnTe detectors and the mechanism of radiation damage caused by neutron and charged particles in CdZnTe detectors.Quasi-hemispherical CdZnTe detector was manufactured to understand the performance in the mixed gamma-neutron detection field.Based on the simulation results with the software of COMSOL,Geant4,and Matlab,the detector structure has been optimized.The CdZnTe detector shows good energy resolutions for ²⁴¹Am,⁵⁷Co,and¹³⁷Cs radiation sources.A linear relationship between the energy positions and spectrum channels indicates that the detector is effective for the precise energy detection from 59.5ke V to 662 ke V.Neutron and gamma ray from a ²⁴¹Am Be radioactive source were detected simultaneously at room temperature.The spectrum shows good energy resolution for neutron capture gamma ray（14.28 ke V FWHM@558 ke V）.Our work demonstrates that the quasi-hemispherical CdZnTe detector is promising for simultaneous detection of neutrons and gamma radiation.SRIM software was used to simulate the interaction between alpha particles and CdZnTe crystal.The planar CdZnTe detector is adapted to detect charged particles,because the range of 5.48 Me V alpha particles in CdZnTe crystal is only 22.2μm.The electrode layer and surface damage layer are two of the main factors affecting charged particle detection.The influence of Au electrodes on the energy resolution of 5.48 Me V alpha particles is 0.5%,and the surface damage layer of CdZnTe crystals could be removed by chemical polishing with bromomethanol solution.5.48 Me V alpha particle resolution of CdZnTe detector is 0.68%in vacuum.Alpha and beta particles can be distinguished by the rise time of pulse waveforms,depending on the different incidence ranges of alpha and beta particles in CdZnTe crystals.We simulated the radiation defect type and amount of CdZnTe crystals after neutron irradiation with the Monte-Carlo software SRIM based on hardball collision model.The calculated data are also compared with experimental results of detector performance and the crystal defect types and concentrations obtained using thermally stimulated current measurement.It was shown that the concentrations of vacancies,interstitials,and related defects increased after neutron irradiation,which could be the reason for the worsening of CdZnTe detector performance after the neutron irradiation.The energy resolution of CdZnTe detector after 10¹⁰ cm^-2 neutron irradiation could be improved by decreasing temperature,while this method doesn’t work when the neutron irradiation doses is excessive.After a long period of neutron irradiation,the atoms in CdZnTe crystal are activated and become radioactive.The main possible radioactive elements are ^125mTe and115Cd.Defects of charged particles introduced in CdZnTe crystal were simulated by SRIM software.Results showed that particles with large atomic mass have a shorter range in CdZnTe crystals,and at the same time,the scattering angle when they collide elastically with atoms is also smaller.He ions are mainly deposited at the end of the incident track,and the induced displacement damage is also concentrated at the end of the track.However,Kr ions are distributed in the whole track path and induce displacement damage in the whole range as well.Since a large number of carrier trapping centers and recombination centers were introduced by irradiation,the leakage current,carrier mobility and energy spectral performance of the detector are all deteriorated significantly after 3 MeV Kr ion irradiation.The ratio of nuclear collisions in 3 MeV Kr ion irradiation in CdZnTe detector is greater than 2.08 Ge V Kr ion irradiation and therefore creates more damage.The influence of irradiation on the properties of Au/CdZnTe/Au structure detectors with a Schottky barrier on the interface are investigated.The current transport across the Au/CdZnTe junction is described by the diffusion process.Both neutron and 3 MeV Kr ions irradiation may lead to the decline of Au-CdZnTe Schottky barrier.The observed variation of Au/CdZnTe interface states is mainly attributed to the defects and electron traps induced by irradiation.Au atoms collide into CdZnTe crystal forming an acceptor level at 263 me V above the valence band might cause electron tunneling.Photoconductivity properties of CdZnTe detectors show that irradiation induces electrons tunneling through Au/CdZnTe barrier.