Delta-Doped Diamond via in-situ Plasma-Distance Control

Abstract

We present an approach for the CVD growth of diamond, where the sample is placed in 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, leading 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 more than 10 mm away from the plasma, no growth is observed. Instead, we assume a deposition of nitrogen-rich species on the diamond surface, which is incorporated during the growth of the following layer. All fabricated layers show NV emission, where the intensity correlates with the nitrogen incorporation. The growth techniques could allow 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 applicable not only for nitrogen incorporation but also for other defects, for example, phosphorus, which could open up new avenues for diamond-based electronics.

Figures (4)

• Figure 1: Illustration showing the different positions of the sample (2) with respect to the baseplate (1). The sample size is not to scale. a) The sample holder lies at the same level as the baseplate, with the sample in the plasma (reference position). b) The sample holder is far away from the baseplate level, which interrupts the diamond growth process. c) Intermediate positions, where the growth is influenced by the exact position of the sample. d) Image of a sample in the reactor in the reference position, as shown in a).
• Figure 2: ToF-SIMS profile of sample S1, showing the layer stack of six doped layers (blue). The distance $d$ to the base plate was varied in each of the grown layers (20, 10, 0.1, 15, 5, 3 mm), starting from the substrate, as indicated for each layer above the graph. The layers are also indicated by the dip in the 13C concentration (black).
• Figure 3: ToF-SIMS profile of sample S2, where the growth time at a distance $d=20~$mm was varied (35, 10, 5, 1, 2, 20 min from substrate), as indicated for each layer above the graph. No dip in the 13C concentration is observed (black), which indicates a negligible diamond growth rate when the sample is in this position, with nitrogen as the source gas. The nitrogen incorporation in the layers (blue) increases linearly with increasing growth time, as shown in the inset.
• Figure 4: Example spectra from bright spots of the PL slices, shown in a) to c). a) Depth slice through sample S3, grown 0.1 mm below the reference position. b) and c) Depth slice through sample S4 and S5, where the doped layer was grown 3 mm and 20 mm below the baseplate level. The color scale on the right side is valid for all plots, a) to c).