Synthesis And Irradiation Detector Application Of Single Crystal Diamond By MPCVD

Diamond own the excellent properties such as wide band gap,high thermal conductivity and high stability and it is known as"strategic advanced semiconductor material".At present MPCVD（Microwave Plasma Chemical Vapor Deposition）method is definitely the most widely used because of its capability for the preparation of the highest quality diamond films to be used for tool,electronic,thermal,optical,and quantum technology.MPCVD is the most ideal way to prepare large area and high quality diamond because of its advantages such as plasma stability,high electron number density,no electrode pollution,large growth area and excellent quality of diamond film.In this thesis,a combination of physical simulation and experimental research is used to study the MPCVD diamond synthesis process,the behavior evolution of diamond materials under the irradiation of high energy charged particles,and the radiation response of diamond detectors,and the following innovative results were obtained:（1）A microwave plasma discharge simulation under the condition of pure hydrogen was conducted to determine the spatial concentrations of the number density of electron and atom hydrogen in the plasma.Parameters included ionization degree,reflection coefficient and gas temperature were also studied under the condition of lower power and gas pressure.According to the simulation results,the structure of the sample holder was improved,and MPCVD synthesis process of single diamond thick film products was optimized.The problem of the deposition stability of diamond film was solved.The characterization results of the grown single crystal diamond show that the single crystal diamond films have an excellent crystalline structure,with low impurity contents of nitrogen（1.19ppm）and silicon（0.11ppm）.The color grade of the diamond is G color and clarity grade is VS,which lays a foundation for the industrialization of single diamond thick film products.（2）After high energy electron irradiation,the optical properties of diamond materials deteriorate,but the absorption band gap of the materials does not change.Meanwhile,the content of electron radiation defects increases.In the process of electron irradiation,the the nitrogen-vacancy（NV）color centers were further ionized,and the irradiation defects change from NV^-（negatively-charged state）center to NV⁰（neutral form）center.When nitrogen ion is injected into diamond material,the optical transmittance of the material decreases with the increase of the injection amount,and the optical absorption band gap of the material decreases from 5.35e V to 5.08e V.In the process of nitrogen ion implantation,the contents of NV⁰and NV^-color center decreased under the condition of low irradiation dose,but with the increase of irradiation dose,the contents of NV⁰and NV^-color center increased,and the increase rate of NV^-color center was higher than NV⁰color center.The optical transmittance of diamond materials modified by nitrogen ion implantation decreases after electron irradiation,and due to the coupling effect of electron irradiation and nitrogen ion implantation,the content of defects in the material is greatly increased,and the content of NV color center in the material is increased.However,compared with nitrogen ion implantation alone,the content of NV color center is relatively reduced due to the transformation from NV color center to NV⁰color center.Therefore,the content of NV⁰color center is relatively increased.Therefore,the control of NV color center content,especially the control of NV^-color center content,can be realized through the combined effect of the nitrogen content in diamond and electron irradiation.（3）The existence of electrode thickness and air layer has little effect on the radiation response of electrons with continuous energy distribution emitted by single energy electron beam and beta radioactive source in diamond detector.For low energy electron detection of continuous electron spectrum,the detection threshold is the key to affect the detection efficiency.To improve the noise performance of the system,a lower detection threshold can be used to obtain a higher detection efficiency.Forγrays,the response of diamond detector is very low,and the selection of thicker high Z（atomic number）metal electrode can slightly improve the response of low and medium energyγrays.For neutron detection,the diamond detector must add materials containing ⁶Li and ¹⁰B as neutron-sensitive conversion layer materials.The thickness of the conversion material will affect the thermal neutron detection efficiency.When the thickness of the conversion layer increases to a certain extent,the detection efficiency is basically constant.The measurement results of energy spectrum distribution and energy resolution in air and vacuum environment show that the energy divergence caused by gas molecules scattering in air environment will lead to the deterioration of energy resolution ofαradioactive source in diamond detector.These results provide a basis for further improving the performance of diamond detectors in the future.