Diamond films were homoepitaxially grown on type-Ib (1 0 0) diamond substrates by the microwave plasma CVD method at 800 °C with and without doping of S and compared with each other. Source gas was a mixture of H 2 +CH 4 and a dopant gas of SF 6 , the doping amount ranging up to S/C ratio of 24,000 ppm. The FE-SEM image taken from grown films clearly revealed a morphological degradation when SF 6 was doped uniformly during growth, and the more the doping amount, the more degradation developed. The SIMS observation exhibited a marked pile-up of S atoms at the interface between the grown layer and substrate, which was responsible for the morphological degradation. By introducing the Grading–Doping (starting from non-doping), a very smooth surface has been successfully obtained.
