Effect of growth rate on the spatial distributions of dome-shaped Ge islands on Si(001)

Ge/Si(001) layers are grown by gas-source molecular beam epitaxy at 600 degreesC to probe island self-ordering phenomena. We vary the Ge growth rate by a factor of 40, 1.2-47 monolayers (ML) min(-1), and adjust the Ge coverage, 5.9-8.9 ML, to produce films consisting primarily of dome-shaped Ge islands. Measurements of the radial and nearest-neighbor distributions are compared to calculated distributions for random arrangements of circular islands. At low growth rates, island formation is inhibited at small separation. At high growth rates, the angular distributions of nearest-neighbor islands show pronounced island ordering along <100> directions.