In this work, argon, hydrogen and methane are used as gas sources and nitrogen is used as the doping source. Microwave plasma chemical vapor deposition and two-steps deposition processes have been applied to grow the nitrogen-doped diamond thin film on n-type (111) silicon substrate. Systematical experiments are performed to study the dependence of grown process on working pressure, temperature, microwave power, DC bias, the duration of growth time and the flow rates of gas mixture of argon, methane and nitrogen. The nitrogen-doped diamond thin films are examined by SEM, XRD, Raman and I-V. Raman spectroscopy is the most efficient tool for analyzes the quality of diamond thin films growth. The results show that a positive DC bias can enhance the doping concentration and the qualities of diamond thin films. Form the analyzing results, nitrogen is doped in the sp2 structural grain boundaries of crystallites. The longer diamond thin film grown is, the crystallites become larger and the grain boundaries become smaller, that leads to the larger resistivity of the thin films.

The n-type diamond has been shown to be very difficultly synthesized by CVD method. Nitrogen as a donor impurity shows a similar atom size of carbon for diamond lattice. However, nitrogen doped diamond reveals deep level and large carrier activation energy with much defects in diamond. The application of n-type diamond has less reported and the characteristic of nitrogen doped diamond seems varied due to different fabrication process. Our previous study of nitrogen doped diamond using mixture of N2 and argon gas synthesized by microwave CVD indicated that nitrogen atoms were precipitated in the grain boundaries of diamond crystallites. In this paper, it compared the synthesis of nitrogen doped diamond using the mixed gas of nitrogen/CH4/Ar and ammonia/CH4/Ar gases by microwave CVD method for different temperature, gas flow rate, pressure, and microwave power. The conductivities, carrier concentrations and mobility of the n-type doped diamond have been analyzed and discussed. The Hall measurement shows that the mixture of gas with Ar reveals different growth mechanism and carrier transportation properties in diamond. Nitrogen atoms of N2 were located in the grain boundaries and interfaces among diamond crystallites with the sp2 structure. Nitrogen atoms of NH3 are doped into the diamond crystallites.