【作者】 苏青峰；

【导师】 夏义本；

【作者基本信息】 上海大学 ， 材料学， 2007， 博士

【摘要】 CVD金刚石膜具有优异的电学、光学和机械性能，能够耐高温、耐腐蚀和抗强辐射，已成为当前苛刻环境下工作的辐射探测器首选材料。探测器级CVD金刚石薄膜的制备和核探测器件的研制已经成为国际前沿课题。本文通过对金刚石膜光学和电学性能的表征优化了金刚石膜的工艺参数，获得了沉积金刚石膜的最佳工艺条件：衬底温度750℃，碳源浓度0.9％和压强4.0 kPa。成功制备出探测器级（100）定向CVD金刚石膜。与其它取向膜相比，（100）取向金刚石膜具有最平整的表面和最高的质量。使用激光与热化学抛光相结合的复合抛光技术对CVD金刚石膜进行了抛光，使薄膜粗糙度有效降低。采用红外椭圆偏振光谱仪研究了不同取向CVD金刚石膜的光学特性，（100）取向金刚石膜折射率为2.391，分析了影响薄膜光学性能的因素。采用Keithley4200半导体表征系统研究了不同取向金刚石膜的电学特性，分析了退火工艺对薄膜电阻率的影响。采用霍尔效应测试系统研究了金刚石膜载流子浓度和迁移率随温度的变化趋势，分析了影响薄膜霍尔效应的各种因素。室温下（100）取向金刚石膜的电阻率、载流子浓度和迁移率分别为1.9x10¹²Ω·cm，4.28×10⁴cm^-3和76.9 cm²／V·s。研究了薄膜制备过程中氢等离子体处理对金刚石膜光电特性的影响，发现氢等离子体处理可以有效提高薄膜的质量及光电性能，归因于薄膜制备过程中氢离子可消除石墨等非金刚石碳。成功研制了电极条宽25μm间距50μm的金刚石一维列阵粒子探测器，填补了国内研究空白。研究了金刚石与金属的接触特性，分析了金刚石与金属形成欧姆接触的机理，并获得了沉积Cr／Au作为欧姆接触的最佳工艺。研究了金刚石的抗辐照特性，利用5.5 MeV ²⁴¹Amα粒子研究了金刚石探测器的性能。在1 V／μm电场时金刚石探测器的典型性能为：暗电流19.25 pA，净光电流138.07 pA，信噪比7.18，能量分辨率4.65％，电荷收集效率39.27％、电荷收集距离78.54μm。经β粒子预辐照使探测器处于“priming”态，钝化了金刚石膜中的俘获陷阱，使电学特性提高，金刚石探测器的电荷收集效率和工作稳定性得到明显改善，使α粒子电荷收集效率从37.07％提高到了39.27％。首次成功测得了多晶（100）取向金刚石膜的载流子寿命为10.21ns。利用²⁵²Cf中子源研究了CVD金刚石的中子辐照损伤，经中子辐照后金刚石膜的电学和α粒子响应特性明显提高，使α粒子电荷收集效率从38％提高到41.2％，验证了中子也可以使金刚石发生“priming”效应。在获得性能优异金刚石α粒子探测器的基础上，通过在金刚石α粒子探测器点电极面蒸镀一层合适厚度的硼(¹⁰B)转换层，成功研制了金刚石中子探测器。与没有硼(¹⁰B)转换层相比，镀硼之后探测器对中子有明显的能谱响应，在1 V／μm电场时，对中子的探测效率可达1.67％。同时研究了电场强度和硼(¹⁰B)转换层厚度对探测效率的影响。更多还原

【Abstract】 The outstanding optical and electrical properties of diamond film make it an ideal material for radiation detectors in future especially at high temperature, high radiation and corrosion environments. It has been the international interesting subjects that the fabrication of ’detector grade’ CVD diamond films and their applications for detectors.In this paper, the process parameters of CVD diamond film deposition were optimized via measuring optical and electrical properties of diamond films. The optimized process parameters of diamond film deposition of substrate temperature, carbon concentration and chamber pressure are 750℃, 0.9% and 4.0 kPa, respectively. ’Detector grade’ （100）-oriented diamond films were successfully grown on Si substrates. （100）-oriented films have the smoothest surface and fewer concentrations of defects, thus showing better crystal quality than （111） or randomly oriented diamond films. The smooth surface of CVD diamond film was obtained by a composite technique of laser polishing and hot chemical polishing.Optical properties of variously textured diamond films were measured using infrared spectrometric ellipsometery in the wavelength range of 2.5～12.5μm. Refractive index of （100）-oriented diamond film is 2.391. The influence of diamond films microstructure on optical properties was analyzed in detail. Electrical properties of variously textured diamond films had been measured using Keithley4200 semiconductor characterization system and Accent 5500PC Hall effect measurement system. The influence of annealing processing and temperature on resistivity and Hall Effect of diamond films were analyzed in detail. The resistivity, carrier concentration and mobility of （100）-oriented diamond film in room temperature were 1.9×10¹²Ω.cm, 4.28×10⁴ cm^-3 and 76.9 cm²/V·s, respectively. The quality and electrical properties of diamond films were increased observably by hydrogen plasma etching, which attributed to the non-diamond phase in films etched off during the process of deposition.CVD diamond micro-strip detector with strips of 25μm in width and 50μm between strips was successfully fabricated for the first time at home. Electrode contact properties and mechanisms between diamond and metals were investigated. The optimal process of Cr/Au deposition as ohmic contact was obtained. 5.5 MeV ²⁴¹Amαparticles were used to measure the performance of diamond detector. At an applied electric field of 1 V/μm, many significant results were achieved, e.g. the dark-current is of 19.25 pA, the net-current of 138.07 pA, the signal-to-noise ratio of 7.18, the energy resolution of 4.65%, the charge collection efficiency of 39.27% and the charge collection distance of 78.54μm. By pre-irradiatation withβparticles, ’priming’ effect was attributed to traps being filled and passivated. The charge collection efficiency was dramatically improved from 37.07% to 39.27% due to the ’priming’ effect. The carrier life time of （100）-textured diamond with a value of 10.21 ns was measured for the first time.After ²⁵²Cf neutron irradiation, electrical properties and response to a particle of diamond detector increased evidently, which confirmed ’priming’ effect also may take place in diamond by neutron irradiation. The charge collection efficiency to a particle was improved from 38% to 41.2%. On the basis of outstanding properties of diamond particle detector, diamond neutron detector was successfully developed by evaporating a layer of ¹⁰B converter with a proper thickness on the surface of diamond a particle detector. Compared with no converter, remarkable response to neutron of diamond detector with a ¹⁰B converter was obtained. At an electric field of 1 V/μm, the detecting efficiency to neutron was 1.67%. The influences of electric field and converter thickness on detecting efficiency were also investigated.更多还原