IMPURITY INCORPORATION AND DOPING OF DIAMOND

Electronic applications require the ability to dope diamond p- and n-t ype. Boron is well known to dope both natural and synthetic diamond p- type. N-type doping, however, has proven exceedingly difficult. In thi s work, the suitability of several impurities for n-type doping is inv estigated 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 calcul ations were carried out using local density theory, the pseudopotentia l formalism, and the Car-Parrinello method. The impurities were embedd ed in a large supercell and atomic relaxations were computed using ab initio forces. The impurities Li, Na and P are shown to be shallow don ors, but they have very low solubilities. This makes their incorporati on via in-diffusion difficult and leaves ion implantation and possibly incorporation during growth as the only alternatives. Once incorporat ed, 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 oc cupies an interstitial site. It is particularly appropriate for ion im plantation, since no self-implantation step to create vacant sites is necessary.