High-fluence Si-implanted diamond: formation of SiC nanocrystals and sheet resistance

The sheet resistance and structural properties of high-fluence Si-implanted diamond were investigated. In order to minimize the radiation damage and to facilitate SiC formation the implantation was performed at 900 °C. All samples were subsequently annealed in an rf-heated furnace at 1500 °C for 10 minutes in order to remove defects and thermally unstable phases. X-ray diffraction, infrared absorption spectrometry and high-resolution cross-sectional transmission electron microscopy revealed the formation of a buried layer inside the implanted diamond, which contains SiC nanocrystallites. These SiC nanocrystals have a cubic structure and are nearly perfectly aligned with the diamond lattice. Raman spectroscopy was applied to analyze radiation-damage-induced graphitization in dependence on the implantation conditions. The sheet resistance of the samples was measured as function of temperature by four point probe technique in van-der-Pauw geometry. The decrease of the sheet resistance with increasing ion fluence unambiguously shows the influence of implantation-induced damage. The behavior of the sheet resistance can strongly be modified by additional nitrogen implantation The resulting higher conductivity is interpreted as partial incorporation of the nitrogen donor into the SiC nanocrystals. However, when the Si fluence exceeds a critical value of 5.3×1017 Si+cm-2 at 900 °C the diamond is irreversibly damaged and defect related conductivity dominates.