The cause of suppression of the diamond nucleation density

The nucleation density of diamond produced by chemical vapor deposition (CVD) is greatly dependent on the plasma density and the surface state of the substrate. The nucleation density of diamond can be increased by pretreating optimally the substrate surface. The scratching and biasing methods are both excellent substrate treatments. In particular, the biasing method enables elucidation of the nucleation mechanism while also enabling control of the nucleation process. In the present study, we combined the biasing method with the hydrogen etching method and studied the effect of these methods on the nucleation density of diamond. The results indicate that there is a threshold time required for nucleation to take place. By appropriate combination of the two processes, the nucleation density was increased to 10(12) cm(-2). In addition, we studied the cause of suppression of the nucleation density and found that the nucleation density is dependent on both the height of nuclei and their distance from one another, and that suppression is caused by insufficient delivery of source gas. We demonstrated how this lack of source gas explains the decrease in nucleation density using the scratching method. Based on the critical size of the nuclei, we estimate that the maximum nucleation density of diamond obtainable by the biasing treatment method is 10(14) cm(-2) under optimal conditions.