Ultraheavy boron doping of diamond by ion implantation for low-resistance layer formation: Effect of hot implantation

We performed heavy boron doping of diamond at high concentrations from 1019 to 1021cm−3 using ion implantation at various substrate temperatures to form a low-resistance p-type layer. This study details the electrical properties and crystallinity as a function of implantation temperature and discusses the potential for extremely heavy B doping. At room temperature, heavy B doping with a concentration of 3.5×1020cm−3 drastically reduced resistivity to approximately 10−3Ωcm, nearly comparable to that of graphite. Raman and Rutherford backscattering spectra confirmed the formation of a graphitized layer in the B-implanted region. In contrast, the crystallinity was maintained in samples B-implanted at 400 and 800 °C with the same doping concentration. A Raman peak at 1332 cm−1, corresponding to the diamond structure, was still observed in samples implanted at 400 and 800 °C even at a concentration of 3.5×1021cm−3 (2 at. %). The specific resistance was low (approximately 10−3Ωcm), and p-type conductivity was observed across all measured temperatures. These results clearly indicate that hot implantation above 400 °C is effective for achieving heavy doping of a few percent, forming a low-resistance layer while preserving the crystallinity of diamond.