Impact of Nitrogen Concentration on Monocrystalline Diamond Growth in Microwave Plasma Chemical Vapor Deposition

The influence of the nitrogen concentration on monocrystalline diamond growth in microwave plasma chemical vapor deposition was investigated with optical emission spectroscopy (OES) and Raman spectroscopy for growth condition optimization. The results show that the added nitrogen concentration has a major impact. To be specific, as the N₂-concentration increased, the intensity of CN radicals and the deposition rate increased, accompanied by a decrease of the C₂ groups. At a N₂-concentration below 0. 5%, high quality diamond grain grew rapidly, possibly because N₂ catalyzed the surface reaction and surface crystallization instead of promoting decomposition rate of methane molecules; however, at a N₂-concentration over 0. 8%, the diamond quality slowly deteriorated, though the deposition rate remained almost unchanged, simply due to increasing formation of non-diamond phase.