Design And Research Of Array X-ray Detector Based On Lead Iodide Material

Lead iodide(PbI2)crystal is a new kind of material for room temperature nuclear radiation detectors with the advantages of low melting point,large atomic number,high resistivity,high density,high physical and chemical stability and so on.It can detect y-ray or X-ray among 1 KeV?1 MeV and has great application value in the field of room temperature nuclear radiation detector.Energy resolution of high energy ray can be realized by the array detector based on PbI2 crystal with lower dark current at room temperature.Without additional cooling measures,the structure of the detector is simple,and it has many advantages over the same type of detector.Therefore,PbI2 array X-ray detector has become one of the research hotspots in the field of radiation detection materials and devices in recent years,and it has important application prospects in the fields of environmental monitoring,astronomical research,biomedical,nuclear physics experiments and related instruments.During the fabrication of the PbI2 array detector,the quality of the crystal,the surface treatment of the crystal and the design of the detector electrode were the key factors which determined the performance of the PbI2 array detector.The paper has carried on the thorough research for the key questions of PbI2 crystal growth procedure,crystal surface treating technology,electrode contact,electrode design and photoelectric performance characterization of the detector,and obtained the certain achievements that were summed up as following:1.PbI2 crystals were grown by horizontal zone melting.The best process parameters for crystal growth were investigated,and the bulk PbI2 single crystal with high quality was obtained.The designed horizontal zone melting device effectively solved the problem of PbI2 steam segregation in the process of conventional zone melting growth.2.The surface morphology,optical property and electrical properties of these PbI2 crystals which were treated by different surface treating technology were studied.The laser induced surface recrystallization technique was used to treat the crystal surface for the first time,and the performance of the detector was improved significantly.3.In order to achieve good electrical contact,the electrode contact layer was fabricated with Au?C?Cu and Al materials.Compared with the I-V characteristics of the detector,the leakage current was minimized by Au-PbI2 contact whose linear fitting effect was the best,and the ohmic contact performance was the best.Therefore,Au was chosen as electrode material in the fabrication of PbI2 detector.4.In order to explore the best way of electrode design,Maxwell software was used to simulate the electric field distribution of detectors with different electrode structure,electrode shape and electrode size.The analysis showed that the electric field distribution of the planar detector was very uniform,and the carrier basically moved along the straight line.What's more,the electric field intensity of circular electrode detector was slightly larger than that of square electrode detector,and the electric field distribution was more uniform.Meanwhile,with the decrease of electrode size,uniformity of electric field distribution was better.The direct relationship between the electric field distribution and the detection performance of the device was proved.5.The prototype of PbI2 array detector for X-ray detection was fabricated,and its electrical and radiation response characteristics were compared.The results were consistent with those of the simulation:The difference of sensitivity between planar and coplanar detectors was not obvious,the SNR of the former was slightly smaller,and the response time was slightly larger.What,s more,the sensitivity and SNR of circular array detector were larger than that of square array detector,and the response time was shorter.Meanwhile,the response time and dark current of the small electrode detector were smaller and the SNR was higher.In conclusion,the Au/PbI2/Au array detector with a small electrode size(radius of 0.5 mm)and circular electrode shape was the most suitable electrode design parameter.