Coupled effect of nitrogen addition and surface temperature on the morphology and the kinetics of thick CVD diamond single crystals

In this study, homoepitaxial thick diamond films were grown by CVD at high microwave power densities for temperatures ranging from 800 degrees C to 950 degrees C and with nitrogen additions from 75 to 200 ppm relative to the total gas flow. It was observed that there is a coupled effect of these two parameters on the growth mechanisms of the CVD diamond film. For a deposition temperature close to 875 degrees C and for the lowest nitrogen concentration, the growth proceeded via a step flow mode identified by classical step bunching phenomena due to the presence of nitrogen and leading to the appearance of macro-steps. When nitrogen concentration was increased keeping the same temperature, the growth mode evolved from a step flow mode to a bidimensional nucleation mode, for which macro-steps are no longer observed. For higher growth temperatures (950 degrees C), it was found that this growth mode transition still exists but appears for much higher nitrogen concentration. These different observations, associated with the resulting growth rates, are discussed in terms of surface modification induced by the presence of nitrogen impurity. It is shown in particular that an increase of nitrogen concentration is equivalent to an increase of the surface supersaturation, this effect being compensated by an increase of the deposition temperature. (C) 2006 Elsevier B.V. All rights reserved.