A first principles study of lithium, sodium and aluminum in diamond

Abstract

Although diamond has been successfully n-type doped with phosphorus, the search for shallower n-type dopants in diamond has continued. Interstitial Li and Na have been predicted to be shallow donors, however, experimental results have been contradictory. Aluminum, if incorporated, may be expected to form an acceptor in the same way as boron, and it too was modeled here. We report ab initio Density Functional Theory modeling of Li, Na and Al in diamond and show that although interstitial lithium and sodium are shallow donors, interstitial Li will readily diffuse and that it is favorable for migrating Li to be trapped at vacancies. The resulting substitutional Li is not only passivated but also compensates remaining interstitial donors, explaining the high resistivity or electrical inactivity observed in Li doped diamond. Na is shown to be most stable as a substitutional acceptor, in agreement with Na diffusing as a negative ion in diamond. Substitutional aluminum is found to induce a deep acceptor level in the band gap, much deeper than the boron acceptor level, inducing greater distortion of the host lattice.