A method for producing homoepitaxial diamond thin film is provided which includes a step of effecting plasma assisted CVD with the carbon source concentration of a mixed gas of a carbon source and hydrogen set to a first low level for depositing a high-quality homoepitaxial diamond thin film on a substrate at a low film forming rate and a step of thereafter effecting the plasma assisted CVD with said carbon source concentration set to a second level higher than the first level. An apparatus is provided for carrying out the method. IMAGE
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