First-principles calculations were made of the behavior of S point defects in crystalline and amorphous Si structures. By introducing the S point defects at various representative positions in the samples, including substitutional and interstitial sites in the crystal and fourfold coordinated or miscoordinated sites (dangling bond and floating bond sites) in the amorphous, the energetics were analyzed in detail and the most stable structures were determined. Two important conclusions were drawn: (a) in crystalline Si, the S defects form pairs in which the two S atoms were energetically bound but not covalently bonded; (b) in amorphous Si, they preferentially occupy threefold coordinated sites, even when the starting configuration had higher coordination (four- or fivefold). The implications of these results for the electronic structure of sulfur-doped Si samples were also analyzed in the context of the present calculations.

Sulfur Point Defects in Crystalline and Amorphous Silicon. Y.Mo, M.Z.Bazant, E.Kaxiras: Physical Review B, 2004, 70[20], 205210 (10pp)