Effects of mobility of small islands on growth in molecular-beam epitaxy

The effects of mobility of small islands on island growth in molecular-beam epitaxy are studied. It is shown that mobility of small islands affects both the scaling and morphology of islands during growth. Three microscopic models are considered, in which the critical island sizes are i*=1, 2, and 3 (such that islands of size s less than or equal to i* are mobile, while islands of size s greater than or equal to i*+1 are immobile). As i* increases, islands become more compact, while the exponent gamma, which relates the island density to deposition rate, increases. The morphological changes are quantified by using fractal analysis. It is shown that the fractal dimensions an rather insensitive to changes in i*. However, the prefactors provide a quantitative measure of the changing morphologies.