The Research On CVD Diamond Films And Radiation Detectors

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 1.9×10¹²Î©.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.