Change of structural and electrical properties of diamond with high-dose ion implantation at elevated temperatures: Dependences on donor/acceptor impurity species

We have investigated phase transformation, optical and electrical properties of diamond implanted with high dose (up to ∼1021 cm−3) B, P and N acted as donor or acceptor elements in diamond, at elevated temperatures in the medium energy range (30 to several 100 eV) followed by post-implantation annealing. Unlike a typical semiconductor such as Si, the high dose ion implantation over critical dose Dc to diamond below about room temperature results in phase transformation to a thermally stable graphitic phase after a post-implantation annealing process. In this study, it was found that any diamonds B-, N- and P-implanted at high doses at elevated temperatures (∼400 °C) maintain diamond structures (graphite transformation does not occur) after annealing, from the results of optical absorption spectra, Raman scattering and temperature dependence of electrical properties. In the case of B and N, not only graphitization was avoided but also resistivities were reduced after annealing. In particular, in the B doped samples high electrical activation of B acceptors occurred, and heavily B doped (∼2.5 × 1021 cm−3) diamond became a p-type degenerate semiconductor with low resistivity due to a metal-like band structure. In the N doped sample, the resistivity was ∼103 times as high as that in the B doped sample, but the value was much lower than normal diamond as an insulator. This suggests that in the N doped sample only impurity band conduction occured unlike the B dope samples. On the other hand, the resistivity of the P doped sample was ∼106 times as high as that of the N doped sample. This result most likely means that graphitization was avoided, also in the P doped sample, while the high mass number element P compared with B and N induced many radiation defects (not annealed out) in diamond acting as carrier trapping, and the resultant resistivity became very high.