Phosphine Adsorption and Dissociation on the Si(001) Surface: An Ab Initio Survey of Structures

The continued down-scaling of electronic components to the atomic scale leads to a number of novel devices including quantum cellular automata, single electon transistors and quantum computers. The fabrication of such devices invariably requires scanning probe microscopies and an atomic-level understanding of doping mechanisms and the intermediate species involved. In the case of phosphorus, it is well established that PH$_3$ adsorbs dissociatively on the Si(001) surface, much controversy surrounds the numerous intermediate species observed in STM experiments. We present an extensive density functional theory (DFT) survey of possible PH$_3$ dissociation products and assign three prominent STM features as PH$_2$, PH and P species, respectively. All three structures are fully consistent with STM data and collectively outline a mechanism for the complete PH$_3$ dissociation on the Si(001) surface.