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 similar to 10(21) 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 D-c 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 (similar to 400 degrees 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 (similar to 2.5 x 10(21) 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 similar to 10(3) 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 similar to 10(6) 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. (C) 2011 Elsevier B.V. All rights reserved.