Local structures of phosphorus atoms implanted in crystalline diamond

Effective impurity doping into diamond by an ion implantation technique has been one of the crucial issues for realizing diamond-based high-power electronic devices. Especially for n-type impurity doping, the electrical activation has not been accomplished yet in a practically available level. In this study, local structures and depth profiles of implanted phosphorus atoms were studied by x-ray absorption spectroscopy, secondary ion mass spectroscopy, and first-principles calculations. P ion implantations were performed at two extreme substrate temperatures of room temperature and 900°C at multiple incident energies from 10 to 150 keV for flat doping and a single energy of 200 keV for δ-doping followed by activation annealing at 1300°C. The x-ray absorption spectra and the theoretical calculation showed that most of the implanted phosphorus atoms implanted with a flat doping concentration are existent in the substitutional site; however, they seem to bond with hydroxyl or vacancy complexes, probably resulting in electrical inactivation. Indeed, secondary ion mass analysis showed that a large number of O and H atoms are distributed in the P-doped layer, probably diffused from the surface through a damaged network. On the other hand, impurity diffusion was not observed in the P δ-doped sample followed by high-temperature annealing with a cap layer. It is clearly suggested that a damaged layer by ion irradiation near the surface acts as diffusion channels and trap sites of various impurities. High-temperature annealing with a cap layer is also quite effective in suppressing the formation of the defective layer that becomes a diffusion path of O and H.