Conduction in ion implanted single crystal diamond

We have implanted sodium, phosphorus and arsenic into single crystal type IIa diamond as possible n-type dopants. Particular emphasis was applied to the implantation of sodium at different temperatures and doses; combined implantation energies of 55,80 and 120 keV were used to provide a uniformly doped layer over approximately 100 nm depth. The implanted layers exhibited semiconducting behavior with a single exponential activation energy between 0.40 and 0.48 eV, as determined by temperature dependent resistance measurements. A sample implanted to a concentration of 5.1019 Na+/cm3 at 550 degrees C exhibited a single activation energy of 0.415 eV over a temperature range from 25 to 500 degrees C. Thermal annealing above 900 degrees C was found to remove implantation damage as measured by optical absorption and RBS/channeling. However, concomitant increases in the resistance and the activation energy were observed. Implantation of 22Ne was used to introduce a damage density equivalent to the 23Na implant, while not introducing an electrically active species. The activation energy and electrical resistance were similar but higher than those produced by implantation with sodium. We conclude that the electrical properties of the Na-implanted samples were at least partly due to electrically active Na, but that residual implantation damage was still important