Phosphine adsorption and dissociation on the Si(001) surface: An ab initio survey of structures

We report a comprehensive ab initio survey of possible dissociation intermediates of phosphine (PH₃) on the Si(001) surface. We assign three scanning tunneling microscopy (STM) features, commonly observed in room-temperature dosing experiments, to PH₂+H, PH+2H, and P+3H species, respectively, on the basis of calculated energetics and STM simulation. These assignments and a time series of STM images which shows these three STM features converting into another, allow us to outline a mechanism for the complete dissociation of phosphine on the Si(001) surface. This mechanism closes an important gap in the understanding of the doping process of semiconductor devices.