Delta-doped diamond via in situ plasma-distance control

We present an approach to CVD diamond growth, in which the sample is placed at a defined distance from the reactor baseplate, to which the plasma couples. We observe two previously unknown growth regimes. In the first case, the sample is positioned within three to five millimeters of the plasma. This leads to a decreased growth rate, compared to a position inside the plasma and, additionally, to an increased nitrogen incorporation, allowing the fabrication of delta-doped layers with a thickness below 30 nm. In another regime, where the sample is positioned more than 10 mm away from the plasma, no growth is observed. Instead, we assume that a thin layer of nitrogen-rich species on the diamond surface is formed, which is incorporated during the growth of the following layer. This enables the fabrication of delta-doped layers with thicknesses below 10 nm. All doped layers show NV emission, with the intensity correlating with the nitrogen incorporation. The growth techniques could enable the fabrication of highly doped thin films for quantum sensing applications, as well as layers with low NV concentration, for quantum computing. The new approaches are not only applicable to nitrogen incorporation but also to other dopants such as phosphorus, which could open up new avenues for diamond-based electronics.