射线探测用碲锌镉晶体及其器件研究

Research on the Cadmium Zinc Telluride Crystal and Its Device for Radiative Ray Detection

采用改进的布里奇曼(B ridgm an)方法进行锌组分为0.15碲锌镉(Cd0.85Zn0.15Te)晶体的生长。通过严格控制晶体生长过程中Cd的蒸气分压,使得所生长的碲锌镉晶体在结晶质量方面达到了较好的水平。对其性能进行测试,红外透射比T>60%、沉积相密度<1×104/cm2、位错腐蚀坑密度DEPD<6×104/cm2、X射线衍射双晶回摆曲线半峰全宽FWHM<20 arcsec、电阻率ρ>1010Ω.cm。利用所生长的晶体初步制作了平面型单元碲锌镉射线探测器,所用晶体的尺寸为5 mm×5 mm×2.5 mm,制成的探测器在室温下对125I和241Am放射源进行了探测测量。对125I放射源,探测出了强度为74.5%的27.5 keV的γ射线特征峰,不能仔细分辨出强度为39.8%的27.2 keV的γ射线特征结构;对241Am放射源,探测出了59.5 keV的γ射线特征峰,分辨率优于6 keV,半峰全宽FWHM<10%,同时还能检测出Te、Cd的X射线逃逸的混合峰以及241Am低能Te-K系、Np-L系的两个X射线特征峰。

Cadmium zinc telluride （Cd1-yZnyTe, CZT） is the first choice of material for room temperature X- ray and gamma-ray detectors. The common growth techniques are the conventional vertical Bridgman and the high pressure Bridgman method. CZT＇s large average atomic number, Z -50, makes photoelectric absorption the dominant interaction below 250 keV, and its high density, 5.8 g/cm^3, results in short interaction lengths. CZT＇s large band gap also results in low leakage current and low noise at room temperature. In this research work, the improved vertical Bridgman crystal growth method is used to grow CZT crystal with a nominal Zn concentration of 15 atomic percent, namely Cd0.85Zn0.15Te. Through by strictly controlling of the cadmium vapor pressure, the high quality CZT ingots were obtained. The characterization by several method of CZT wafer resulted in, FTIR transmittance T 〉 60% within spectra range 2.5 - 20μm at room temperature, the density of precipitate 〈 1×10^4/cm^2 with the precipitate diameter ≤ 15 μm, dislocation etch pit density DEPD 〈 6 × 10^4/cm^2, full width at half-maximum of X-ray rocking curve values FWHM 〈 20 arcsec with the Cu Kal radiation and Si three-crystal inonochromator and 15 mm × 15 mm spot size, the electrical resistivity p 〉 10^10 Ω· cm. The single element planar detector for radiative ray detection fabricated with CZT crystal mentioned above is performed. The size-of CZT crystal for detector is 5 mm× 5 mm × 2.5 mm. On both sides of 5 mm × 5 mm surface, gold and gold/platinum were evaporated as electrodes. The energy spectra to standard radiation source ^125I and ^241Am were performed by CZT planar detector. The applied bias voltage for CZT planar detector is 200 V. The characteristic γ-radiation peak of ^125I at 27.5 keV with intensity 74.5% is detected and the characteristic γ-radiation peak of ^125I at 27.2 keV with intensity 39.8% can not be recognized from the energy spectrum for ^125I. The characteristic γ-radiation peak of ^241Am at 59.5 keV is measured with the full width at half-maximum FWHM 〈 10%, v/z. the resolution is better than 6 keV. In the mean time, the characteristic X- ray escape mixing peaks of tellurium and cadmium located at 34 keV is detected and two characteristic Xradiation peaks of Te-Kα1,α2 at 27 keV and Np-Lβ1 at 17.5 keV are also recognized