First principle of palladium-defect pairing in doped Si

Full text: The electric field gradient (EFG) measured by hyperfine interaction techniques, e.g. time-differential perturbed angular correlation (TDPAC), provides relevant information about the interaction of probe atoms like ¹⁰⁰Pd/¹⁰⁰Rh with other defects. TDPAC study of palladium (Pd) in doped Si identified two possible Pd-defect pairings. Pd-vacancy pairing was observed in n-type Si irrespective of the dopant (P, As and Sb) type while Pd-B pairing was observed in B-doped p-type silicon. In Ge, however, TDPAC measurements confirmed that Pd pairs with vacancy in both n- and p-type dopants (Sb and Ga). The question that arises is why is Pd pairing with dopant in p-type Si but with vacancy in p-type Ge? TDPAC data interpretation and assigning of a particular defect configuration to the EFG of the defect complex is a very difficult task. This paper aims at complementing the understanding of the pairing of Pd with defects in silicon using Density Functional Theory (DFT). The DFT calculations confirmed the observed palladium-defect pairing in both the nand p-type Si. However, the Pd atom is located on bond-centred site in Si instead of on the substitutional site as observed in n-type Si. Based on the calculations, we deduce that Pd occupies the interstitial site to pair with B in B-doped Si because of the small atomic size of B relative to its host material Si. (author)