Annealing of ion-implanted defects in diamond by MeV ion-beam irradiation

Abstract

Defects and amorphous C layers or clusters in a type-Ib diamond formed by C- or P-ion implantation under certain doses are clearly annealed or epitaxially crystallized during thermal annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C or during mega-electron-volt (MeV) ion-beam irradiation at 750 \ifmmode^\circ\else\textdegree\fi{}C. Implanted P atoms are incorporated into substitutional sites after complete crystallization by using MeV-ion-beam irradiation. This is confirmed by using the Rutherford-backscattering-spectroscopy channeling method. A considerable amount of defects or amorphous clusters are formed by C-ion implantation at a 50-keV energy for a $1\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose. However, they are crystallized epitaxially to the crystalline diamond by using only thermal annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C or by using MeV-ion-beam irradiation at 750 \ifmmode^\circ\else\textdegree\fi{}C. Above $2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ C doses, continuous amorphous layers are formed internally in the substrate and epitaxial crystallizations proceed from both the crystalline substrate and the crystalline-surface region. Moreover, the rate of crystallization is higher for annealing with MeV-ion-beam irradiation than for thermal annealing at the same temperature. Epitaxial crystallization of the internal amorphous layer, however, stops in both thermal annealing and MeV-ion-beam irradiation, even if annealing time or irradiation dose increases. This is probably due to amorphous C changing into the graphite layers that occurs during thermal annealing or MeV-ion-beam irradiation. Graphite formation is also observed for the as implanted sample before annealing. Direct evidence of graphite formation is given from the channeling yield difference between samples for a $2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose and for a $3\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose, showing clearly the stopping power difference between ${\mathrm{sp}}^{2}$ (graphite) and ${\mathrm{sp}}^{3}$ (diamond) bonding. Amorphous layers in diamond can be formed by C-ion implantation at a more than one order of magnitude smaller amount of doses, compared with those needed for the amorphization of the Si substrates. A calculated number of vacancies created per incident C ion in Si is larger than in diamond. Nevertheless, diamond is amorphized faster than Si. A mechanism is proposed for forming the amorphous layer in diamond. This consists of a bond-breaking process due to inelastic electronic scattering and the movement process of C atoms after bond breaking with the assistance of elastic nuclear scattering without recoil, induced by ion implantation. Atomistic models for ion-beam-induced epitaxial crystallization (IBIEC) and for low-temperature crystallization of implantation-amorphized epitaxial Si layer formed by ultrahigh vacuum chemical-vapor deposition are proposed and discussed, putting particular emphasis on the role of both nuclear and electronic scattering of incident MeV-ion beam. A similar atomistic model for the inclusion of implanted P atoms into substitutional sites is also proposed, based on this atomistic IBIEC model.