Simulation Study Of Neutron Radiation Damage To CdZnTe Detector

With the development of national economy and science,cadmium zinc telluride nuclear radiation detector has been widely used in space physics research,medical imaging,environmental monitoring and other aspects.Due to the complexity of the radiation environment,it will cause different degrees of irradiation damage to the detector,which is an important factor that seriously threatens the long-term service of the nuclear radiation detector in the nuclear radiation field.In view of the high cost and complex process of material irradiation damage experiments,and the fact that neutron activation may cause certain difficulties in carrying out experiments,this work will carry out the research on the irradiation damage of neutrons on CdZnTe detectors from two aspects:the generation of microscopic defects in the sensitive area of the detector and the influence of microscopic defects on the macroscopic electrical properties of the detector.This work is mainly divided into two aspects:the generation of microscopic defects and the influence of microscopic defects on macroscopic electrical properties.First of all,the Monte Carlo method is used,that is,the Geant4 package is used to simulate the transport of neutrons with energy in 1～14 Me V in CdZnTe materials,obtain primary knock-on atoms information,including their types,position distribution and energy distribution,and combine with cascade collision models to calculate the displacement damage caused by neutrons of different energies in CdZnTe materials from the aspects of non-ionization energy loss,number of displacement atoms and displacement per atom.The calculation results show that most of the primary knock-on atoms energy are in the low energy end,and with the increase of incident neutron energy,the types of primary knock-on atoms are more abundant,but the total number begins to decrease.After neutron irradiation of CdZnTe,the non-ionizing energy loss showed a uniform distribution with the incidence depth,and the non-ionizing energy loss,like dpa,did not increase linearly with the increase of neutron energy,but showed a trend of increasing first and then decreasing.At the same time,through the energy spectrum and angular distribution of secondary particles,it can be seen that in the case of neutron irradiation,the irradiation damage caused by secondary particles is small.Secondly,the finite element analysis method was used,that is,the TCAD-Silvaco software was used to simulate the effects of different deep level impurity concentrations,different neutron energies（1～14 Me V）,different neutron fluence(1×10¹⁰ n/cm²,1×10¹¹n/cm²,1×10¹² n/cm²)on the electrical properties of CdZnTe detectors.The analysis results show that with the increase of the deep level impurity concentration or the fluence of neutron irradiation,the leakage current of the device,the spatial charge concentration and the internal electric field strength in the area near the cathode increase,and the dead zone range increases,which affects the carrier collection efficiency of the detector.In addition,under the same neutron fluence,with the gradual increase of neutron energy,the leakage current,the spatial charge concentration and the electric field strength near the cathode showed a trend of first increasing and then decreasing,which was the same as the trend of NIEL and dpa with energy.Comprehensively considered,this may be due to different degrees of defects caused by different energy PKA,which in turn introduces different trap energy levels,affects changes in carrier mobility,carrier concentration,etc.,and thus affects the electrical properties of the device.Clarifying the changes in the micro defects and electrical properties of the CdZnTe crystal in the radiation field are the key to understanding the anti-radiation performance of the material,and the specific regulatory mechanism of the shortcomings of the Cd vacancy and other deficiencies to the optoelectronic characteristics of the crystal material.The radiation resistance of the device and the development of the detector that can be served in the nuclear radiation field for a long time has far-reaching significance.