Nanocrystalline Diamond Films Grown in CH4-H2-GeH4-N2 Gas Mixtures: Structure and Luminescent Characteristics

The chemical vapor deposition (CVD) of diamond allows the controllable formation of the material with desirable structure and elemental composition. In this study, Ge-doped microcrystalline and nanocrystalline diamond (NCD) films are synthesized using microwave plasma-assisted CVD in CH₄-H₂-GeH₄-N₂ gas mixtures. We grow series of 2 μm thick NCD films with variations in gas composition [N₂] = 0 − 4% and [CH₄] = 10 − 15%. We investigate and compare the structure, phase composition, and luminescent characteristics of the grown films. The luminescent signals from Silicon vacancy (SiV, 738 nm) and Germanium vacancy (GeV, 602 nm) color centers in diamond are registered. The additional annealing of the as-grown films in air is used to remove the excessive sp² phase that hinders their luminescent properties. For both SiV and GeV centers, we find conditions for CVD growth of NCD films that are as bright or even brighter than Si-doped and Ge-doped high-quality microcrystalline diamond films (MCD) grown without N₂ additions. These results may be used for the fabrication of NCD films and plates with high concentrations of SiV and GeV centers, which may serve as source material for the fabrication of sub-micrometer-sized luminescent diamond particles for local optical thermometry.