Study On TIBr Crystal Growth And Annealing Process

Due to its wide band-gap （2.68eV）, high atomic number （Tl:81, Br:35）, highdensity （7.56g/cm³ï¼‰, high resistivity (about10¹¹ cm), thallium bromide （TlBr） is a verypromising semiconductor nuclear radiation detector material. It is easy to grow TlBr singlecrystals by melt growth techniques because of the relatively low melting temperature（⁴60C） and a simple CsCl cubic lattice structure of the TlBr material. TlBr detectorshave advantages of high energy resolution, wide liner range, short pulse rise time andsmall size, have been widely used in the fields of nuclear medicine, industrialno-destructive testing, environmental monitoring, security check, aerospace, astrophysics.The quality of the TlBr crystals is still a key factor influencing the detector performance.In this paper, the TlBr crystals were grown by electro dynamic gradient method（EDG） and effects of crystals grown in ampoule with different cone angles andatmospheres were investigated. The quartz ampoules with cone angle of12,20and36degrees were used to grow TlBr crystals, the crystal quality were characterized by infrared（IR） transmittance spectrum and XRD patterns. The crystal grown in ampoule with20degrees cone angle obtained the best performance. Different parts of the crystal weremeasured by XRD to study the unification of crystal orientation. Then the crystals weregrown under vacuum, air and oxygen. The crystal quality were characterized and the resultshowed that the quality of crystal grown under oxygen is best, the resistivity is5.64×10¹⁰ cm and the resolution for241Am at room temperature is29.3%。In addition, the paper studied the influence of annealing temperature and atmosphereon wafers’ quality. After annealed at200,250,300,320and340oC，the wafers’ opticaland electrical properties were improved. The best annealing temperature is320oC. Waferswere annealed at320oC under different atmosphere （air, argon, oxygen）, the resultshowed that annealed effect of oxygen is better. During the process of annealing, oxygenatoms diffuse into the wafers and react with Tl precipitates to form Tl₂O. The Tl₂O is verysoluble in TlBr crystal, therefore the Tl precipitates decrease and the optical and electricalproperties are improved. Higher oxygen pressure has better annealing effect. Afterannealed at320oC under1atm oxygen，the wafer’s resistivity is4.90×10¹¹ cm and energy resolution is21.99%.