Hydrogen-induced crystallization of amorphous silicon clusters in a plasma reactor

In the present study, the mechanism of hydrogenated silicon particle nucleation in a plasma reactor is investigated using quantum molecular dynamics (MD) simulations. We can realistically simulate the nanoparticle growth in the plasma by successive collisions of SiH₃ and SiH₄ molecules at room temperature impact energies. Our method permits the simulation of the experimental plasma reactions more realistically than most former investigations, which were mainly limited to minimum energy searches to determine possible Si_nH_m structures, neglecting all dynamical effects of the cluster growth. Consequently, even the formation of metastable amorphous structures (as during powder formation) can be simulated with our method. Our simulations show that cluster growth in a pure silane plasma at room temperature always leads to amorphous silicon structures that are very rich in hydrogen. By exposing those amorphous clusters to atomic hydrogen, however, we observe their crystallization. During the atomic hydrogen exposure, the nanostructures pass through multiple metastable configurations until they eventually fall into a minimum energy configuration. In this case, we obtain Si_nH_m structures that correspond remarkably well to the minimum energy structures predicted by ab initio calculations. To evaluate this striking result more quantitatively, we display the corresponding atomic radial distribution functions. The present method is a new way to investigate realistic nanostructure growth in a less empirical and thus more realistic manner.