| Due to the unique mechanical, thermal, optical, electrical properties and outstanding chemical stability, diamond film is an ideal wide-band-gap semiconductor material for electron devices, especially devices operating at high temperature, high power, high radiation and corrosion environments. It has been the international interesting subjects that the fabrication of CVD diamond films, especially freestanding diamond films with smooth nucleation surface, and their applications for devices. In this thesis, the fabrication of high quality CVD diamond films and their applications in transistors and photodetectors were studied.The freestanding diamond (FSD) films were grown by hot filament chemical vapor deposition (HFCVD) method and microwave plasma chemical vapor deposition (MPCVD) method, respectively. The influence of substrate pretreatment methods on the nucleation density of diamond films was studied. The thickness of FSD films, the structure, and morphology of the FSD nucleation surface were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results indicated that the nucleation sides of FSD films prepared by both methods were very smooth; The growth rate of diamond films was much higher by using HFCVD method. The effects of surface treatment and annealing process on the quality and electrical properties of FSD films were investigated by semiconductor characterization system and Raman spectroscopy. The results showed that the FSD films with better crystal quality could be obtained by MPCVD method.The nucleation sides of FSD films prepared by MPCVD method were exposed to hydrogen plasma treatment. The effects of hydrogen plasma treatment and annealing process on the p-type behavior of FSD films were investigated. The origin of this high-conductivity layer of FSD films was also discussed by using ultraviolet (UV) Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and secondary ion mass spectrometry (SIMS). The main results were as follows: The nucleation side of FSD films with a p-type conductivity layer (~50nm thick) could be obtained by hydrogen plasma treatment; The origin of this conductivity layer may be related to the complexes of absorbed hydrogen atoms with carbon dangling bonds; The sheet carrier concentration of the FSD film increased and sheet resistivity decreased with the time (5-30min) and temperature (600-750oC) of plasma treatment; Surface conductivity of hydrogenated diamond surfaces disappeared gradually after annealing at temperature above 200°C in the air, or above 600°C in the vacuum; The conductive surface layer could also be removed by oxidation using oxygen plasma treatment.The properties of metal contacts on hydrogenated p-type diamond surfaces were discussed. The results suggested that ohmic contacts could be realized between the p-type diamond and the Au electrodes. However, it's easy to form schottky contacts between Al electrodes and the p-type diamond. Preparation technology of p-type channel metal–semiconductor field effect transistors (MESFETs) was studied. The properties of the device were analyzed by semiconductor characterization system, which showed a typical characteristic of enhancement-mode MESFET.The ZnO films were grown on the nucleation sides of FSD substrates by radio-frequency (RF) magnetron sputtering method. The effects of sputtering power, gas pressure and homobuffer layer on the properties of the ZnO film were studied. The ZnO/diamond structure was also applied for UV photodetectors use. The main results were as follows: High quality ZnO films with highly c-axis orientation can be obtained when sputtering power was 150W, gas pressure was 0.3Pa and homobuffer layer was applied; Compared with films prepared without buffer layer, the samples with buffer layer showed a better crystalline quality; The homobuffer layer was also helpful to improve electrical properties and spectral response performance of the ZnO/diamond structure photodetectors.
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