IMPURITY INCORPORATION AND DOPING OF DIAMOND

Electronic applications require the ability to dope diamond p- and n-type. Boron is well known to dope both natural and synthetic diamond p-type. N-type doping, however, has proven exceedingly difficult. In this work, the suitability of several impurities for n-type doping is investigated theoretically. We also examine the well-known nitrogen deep impurity as well as the effect of simultaneous doping with N and B on the thermodynamic equilibrium between diamond and graphite. The calculations were carried out using local density theory, the pseudopotential formalism, and the Car-Parrinello method. The impurities were embedded in a large supercell and atomic relaxations were computed using ab initio forces. The impurities Li, Na and P are shown to be shallow donors, but they have very low solubilities. This makes their incorporation via in-diffusion difficult and leaves ion implantation and possibly incorporation during growth as the only alternatives. Once incorporated, Li is found to be a fast diffuser whereas Na will be stable up to moderate temperatures. The most suitable shallow donor is Na, which occupies an interstitial site. It is particularly appropriate for ion implantation, since no self-implantation step to create vacant sites is necessary.