Formation of low-resistance layer in diamond by ultraheavy N+ doping by ion implantation beyond the CVD doping limit

We report the successful realization of low-resistance layer by high-concentration nitrogen doping in single-crystal diamond using high-temperature ion implantation. While nitrogen has been considered a potential donor in diamond, its deep donor level (∼1.7 eV) and difficulty of activation have limited its practical use in electronic applications. Furthermore, traditional CVD-based doping methods have been constrained by low solubility and poor depth control, with maximum reported N concentrations below ∼3×1020cm−3. In contrast, our approach enables the introduction of nitrogen at concentrations exceeding 1022cm−3 while suppressing the graphitization of the heavily doped region. Electrical measurements using the van der Pauw method revealed a strong dependence of resistivity on doping concentration, with room-temperature resistivity decreasing to ∼100Ωcm at a doping concentration of 1×1022cm−3. The achieved resistivity is comparable to that of phosphorus-doped diamond via chemical vapor deposition. Although precise carrier type and concentration could not be determined due to the dominance of hopping conduction, this study demonstrates, for the first time, that low-resistivity N-doped diamond layers can be fabricated via ion implantation. These results suggest that high-temperature ion implantation offers a practical pathway for forming localized and high-concentration n-type regions in diamond.