Abstract
Thin-film Si grows layer by layer on Si(001)-(2 × 1):H in plasma-enhanced chemical vapor deposition. Here we investigate the reason why this occurs by using quantum chemical molecular dynamics and density functional theory calculations. We propose a dangling bond (DB) diffusion model as an alternative to the SiH3 diffusion model, which is in conflict with first-principles calculation results and does not match the experimental evidence. In our model, DBs diffuse rapidly along an upper layer consisting of Si-H3 sites, and then migrate from the upper layer to a lower layer consisting of Si-H sites. The subsequently incident SiH3 radical is then adsorbed onto the DB in the lower layer, producing two-dimensional growth. We find that DB diffusion appears analogous to H diffusion and can explain the reason why the layer-by-layer growth occurs.
Highlights
Fracture and Reliability Research Institute (FRRI), Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aobaku, Sendai, Miyagi 980-8579, Japan
We propose a dangling bond (DB) diffusion model as an alternative to the SiH3 diffusion model, which is in conflict with first-principles calculation results and does not match the experimental evidence
We www.nature.com/scientificreports found from tight-binding quantum chemical molecular dynamics (MD) simulations that the initial growth of thin-film Si follows an ‘‘abstraction-adsorption’’ mechanism[21,22], where a DB is generated on the surface via H abstraction by a SiH3 radical and the SiH3 radical is adsorbed onto the generated DB
Summary
Our results indicate that the increase in substrate temperatures causes the return of DBs to the upper layer, which decreases the existence probability of DBs in the lower layer, because DBs stay on the upper layer for a long period of time when the SiH3 island size is large. This results in the adsorption of SiH3 radicals onto the upper layer and an increase in surface roughness. Owing to the longer residence time of the DBs at step sites in the lower layer, the SiH3 radical is adsorbed onto a step site in the lower layer, leading to lateral growth We propose that this DB diffusion mechanism explains the layer-by-layer growth in Si PECVD
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