Si-adatom dynamics and mechanisms of the epitaxial growth on a single-height-stepped Si{001} surface

The Si-adatom dynamics on a single-height-stepped Si{001} surface is studied via a combined molecular-dynamics, simplified transition-state theory and time-dependent lattice-gas description using Tersoff’s potential for Si-Si interactions. The energies of adatom binding and migration near ${\mathit{S}}_{\mathit{A}}$, ${\mathit{S}}_{\mathit{B}}$(b) (bonded), and ${\mathit{S}}_{\mathit{B}}$(n) (nonbonded) step edges show that the global minima, 4.28 eV, are in the trenches at the ${\mathit{S}}_{\mathit{B}}$(n) edges. At all other sites, the binding energies are comparable to those on the flat Si{001}-(2×1) surface. We find that if the adatoms are deposited on an ${\mathit{S}}_{\mathit{B}}$ terrace, reflection dominates at the ${\mathit{S}}_{\mathit{A}}$ edge, whereas at the ${\mathit{S}}_{\mathit{B}}$(b) and ${\mathit{S}}_{\mathit{B}}$(n) edges, adatoms step down and migrate in the trenches parallel to the edges. The deposition rate and surface-temperature-dependent reflection, step up, step down, and accommodation probabilities at all three step edges are calculated and used in a simple estimation of step-edge growth coefficients. We find that the allowable surface-temperature range in which a 400-Å-wide ${\mathit{S}}_{\mathit{B}}$ terrace may grow at the ${\mathit{S}}_{\mathit{B}}$(b) and ${\mathit{S}}_{\mathit{B}}$(n) edges is above 800 K for the 0.30 ML/min (where ML denotes monolayer) film deposition rate and above 700 K for the slower 0.03 ML/min film deposition rate. A microscopic model of the growth of ${\mathit{S}}_{\mathit{B}}$ terraces is also presented in which we find that the nature of the growth, by accommodation, at the ${\mathit{S}}_{\mathit{B}}$(b) and ${\mathit{S}}_{\mathit{B}}$(n) edges, is different such that it maintains the roughness of the growing edge of an ${\mathit{S}}_{\mathit{B}}$ terrace.