Pathways for thermal phosphorus desorption from the silicon (001) surface

Abstract

We use density-functional theory and transition-state search methods to characterize the thermal desorption of ${\text{P}}_{2}$ molecules from the phosphorus-doped silicon (001) surface. We compare two desorption pathways, one proceeding via an in-surface P-P homodimer, the other via an on-surface P-P addimer. While intuitive, the homodimer pathway has an overly large reaction barrier which is not consistent with experimental measurements in the literature. Instead, ${\text{P}}_{2}$ desorption proceeds by the alternative addimer pathway which requires the presence of silicon adatoms. We present a simple chemical-potential model which explains the appearance of these adatoms at high temperatures.