Rare earth interstitial-complexes in Ge: Hybrid density functional studies

Abstract We present results of the structural, energetic and electronic properties of rare earth (RE) interstitial-complexes in Ge ( RE Ge Ge i ; for RE: Ce, Pr, Eu, Er and Tm). We used the Heyd, Scuseria, and Ernzerhof (HSE06) hybrid functional within the framework of density functional theory for all calculations. The energy of formation and charge state transition levels of RE Ge Ge i complexes were obtained. For the neutral charge state, the results of the formation energy of the RE Ge Ge i , were between 0.21 and 8.14 eV. Amongst the RE Ge Ge i , while the Ce Ge Ge i was energetically the most favourable with a binding energy of 3.90 eV, Tm Ge Ge i and Er Ge Ge i were not stable with respect to their binding energies. The Ce Ge Ge i induced deep donor level with negative-U ordering, the Pr Ge Ge i induced shallow levels close to the valence band maximum and the Eu Ge Ge i induced a shallow single donor level.