The origin of degradation in electrical properties by ion implantation doping of boron in diamond

We investigated the origin of electrical degradation in ion implantation doping and discussed the lowest limit of doping concentration. In this study, we particularly performed the light B doping of acceptor boron from 1016 to 1017 cm−3 concentrations by ion implantation to clarify the influence of defects induced by ion bombardment to electrical properties. The electrical properties were analyzed by Hall effect measurement compared to theoretical calculations strictly dealing with charge compensation effects. As a result, we clearly observed excellent p-type conduction and an ionization energy of 0.38 eV. The sample with a doping concentration of 2.7 × 1017 cm−3 showed the smallest compensation ratio and the highest mobility of 510 cm2 V−1 s−1 at 300 K. This is the highest value among the previous reports in the Hall mobility observed for B-doped diamond by ion implantation, but still only half of the ideally expected value. On the other hand, the lightly doped diamond with less than 1017 cm−3 concentrations also showed p-type conductivity but a significantly high compensation ratio, and we found a compensating deep donor level at 0.90 eV measured from valence band maximum. Compared to the previous theoretical calculation, it can be the substitutional B and vacancy complex. The compensating donor concentration gradually increased with increasing doping concentration, suggesting that the donor-like centers induced by the doping process with ion implantation probably affect the carrier transport. Fixed space charge generated by acceptor compensation was found to be the most primary factor determining the upper limit of mobility in ion implantation doping.