Step-flow epitaxial growth on two-domain surfaces

Abstract

A general analytical model is presented for the simulation of step-flow epitaxial growth on two-domain surfaces composed of alternating type-A and B terraces. Separate terms are included for adatom attachment and crossing probabilities at ascending and descending steps on each of the two terrace types. The model is used to follow the evolution of terrace size distributions during deposition, focusing primarily on the case of single-terrace adatom migration. Positive attachment asymmetries Δa (i.e., a larger attachment probability at ascending steps) were found, as in the case for one-domain surfaces, to lead to a slow smoothing of size distribution fluctuations. However, even very small negative Δa values result in a rapid increase in fluctuation amplitudes with a tendency toward step bunching and the formation of double-height steps. The two terrace size distributions diverge essentially immediately upon initiating growth since each terrace is bordered by two terraces of the opposite type and only short-range migration is required to stabilize the average widths of the two distributions. Fractional surface coverages fA (B) of A (B) terraces increase at the expense of B (A) terraces when ΔaB (A)≳ΔaA (B). Steady-state average terrace widths are achieved rapidly, within a few monolayers; however, size-distribution standard deviations σ evolve toward steady state slowly (for ΔaA,B≳0) with σA (B)∝exp(−ΔaA (B)θ/λ2) where θ is the number of deposited monolayers and λ is the fluctuation width. Allowing multiterrace migration decreases, under some growth conditions, the rate at which terrace size distributions diverge and introduces oscillations in σA,B(θ). Simulation results are compared with available experimental data.