| With the improvement of the Chemical Vapor Deposition(CVD)diamond films properties including electrical characteristics, the fabrication of electronic devices based on the CVD diamond has been one of hot research subjects in this field. The diamond detector has many unique advantages, such as high signal-noise ratio, simple structure, normal output in extremely harsh surrounding and a tissue equivalent material. In addition, the diamond is non-toxic and inert to tissue fluid. Thus, the diamond is suitable for in - vivo radiation detection. The phase-purity and orientation of polycrystalline diamond films, however, have great effects on the electrical properties and the response to X-ray . In this paper, the relationship between the preparation processes of diamond films with high phase-purity and high-degree [100] preferential orientation and electrical properties and response to X-ray were studied systematically using a bell-jar type MWPCVD (microwave plasma assisted chemical vapor deposition) setup.The effect of growth parameters (methane concentration, substrate temperature, pressure) and different deposited techniques on the quality and the growth of diamond films were studied systematically. Using general nucleation-growth technique, the films with low purity and resistivity were deposited. With nucleation-etching-growth technique,the quality of the diamond films was somewhat improved. With nucleation-etching-growth-etching-growth cyclic deposition technique, the films with the highest purity and resistivity were deposited. Compared with the general technique, higher oriented [100]and higher resistivity (3. 9X10") diamond films can be deposited under the optimal cyclic deposition conditions .The resistivity of films can be increased by 3 orders of magnitude.A simple in-situ Oxygen Nitrogen> Hydrogen plasma etching post treatment method was used for the as-deposited films to improve their surface purity. Electrical measurements demonstrated that the resistivity is increased greatly up to 6 orders of magnitude (from 108 to 10HQ ? cm ). On the meantime, the leak current of radiation detectors was reduced and the signal to noise was improved. The sensitivity of radiation dosimeter was also increased.Dosimeters with simple Pt/Diamond film/Si sandwich structure were made and examined with steady - state X-ray source. The results show that the photocurrent output is proportional to the flux intensity of incident X-ray. But photocurrent signals became stable after 18 minutes due to the polycrystalline structure of the diamond films.The effect of the diamond films constitution and structure on the electrical properties and the response to X-ray was also studied. The results show that for the same orientation such as [100] or [111], the higher the resistivity of the film, the higher purity as well as the higher sensitivity. In addition, with the almost same resisvitity, the dosimeter based on [100] diamond film has higher sensitivity than that based on [111] diamond film .It is account for the better crystal structure, the less grain boundaries as well as the less defects of the [100] diamond film.The effect of preparation processes on the response to X-ray was studied. Purity and resistivity of the diamond films are different in different procedures. The dosimeter based on the films with cyclictechnique has the higher sensitivity than that with other deposition techniques.The effect of different plasma post-treatment methods on the response to X-ray was studied. The X-ray flux-photocurrent characterization also shows that in-situ plasma post-treatment can improve the diamond films sensitivity to X-ray irradiation. In-situ oxygen plasma processing led to better sensitivity of the dosimeters compared with in-situ nitrogen> hydrogen plasma processing .Because it can decrease more effectively the content of graphite and C-H bond in the as-grown films and improve the electrical properties of a new type dosimeter based on the diamond thin films.
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