Ab initiostudy of the diffusion and decomposition pathways ofSiHxspecies on Si(100)

Abstract

Diffusion and decomposition of ${\text{SiH}}_{x}$ species adsorbed on the clean Si(100) surface are processes of relevance for the growth of crystalline silicon by plasma-enhanced chemical vapor deposition. In this work, we report an extensive search of diffusion and decomposition pathways for ${\text{SiH}}_{3}$, ${\text{SiH}}_{2}$, and SiH by means of combined ab initio metadynamics simulations and optimization of minimum-energy reactions paths. We find that on the clean surface ${\text{SiH}}_{3}$ undergoes stepwise decompositions into Si and H adatoms according to ${\text{SiH}}_{3}\ensuremath{\rightarrow}{\text{SiH}}_{2}+\text{H}\ensuremath{\rightarrow}\text{SiH}+2\text{H}\ensuremath{\rightarrow}\text{Si}+3\text{H}$ with an overall reaction barrier of the order of 0.8 eV, consistent with the scenario inferred from secondary ion mass spectroscopy data. The lifetime of ${\text{SiH}}_{3}$ at room temperature calculated within transition state theory in the harmonic approximation is in agreement with experiments. The lifetime of ${\text{SiH}}_{2}$ turns out to be similar to that of ${\text{SiH}}_{3}$. Possible trap states for ${\text{SiH}}_{2}$ are proposed, based on energetics and by comparing calculated scanning tunneling microscope images with experimental data.