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Dopants

Kajihara et. al. [23] systematically investigated potential n-type dopant in diamond by ab initio calculations. In this method, the electronic wave functions are expended in term of plane waves, and pseudopotentials are used to describe the interaction between the valence electrons and the ionic core. Substititional nitrogen and phosphorus, as well as interstitial lithium and sodium were studied, by relaxing the sample untill a minimum total energy was obtained. It was found that nitrogen is a deep donor in diamond, with an activation energy of 1.9 eV, in good aggreement with experiment. The other dopant led to relatively shalow levels, at about 0.3 eV, 0.2 eV and 0.1 eV for sodium, phosphorus, and lithium respectively. The formation energies calculated by this ab initio model were high and positive for the last three species, suggesting that ion implantation is the best method to dope diamond with these atoms, over doping by diffusion, or impuriry introduction during diamond synthesis.



David Saada
2000-06-22