Self-assembled germanium islands grown on (001) silicon substrates by low-pressure chemical vapor deposition

The time evolution of self-assembled Ge islands, during low-pressure chemical vapor deposition (LPCVD) of Ge on Si at 650°C using high growth rates, has been investigated by atomic force microscopy, transmission electron microscopy, and Rutherford backscattering spectrometry. We have found three different island structures. The smallest islands are "lens-shaped" and characterized by a rather narrow size distribution, ≈ 4 nm high and ≈ 20 nm wide. Next to form are a distinct population of larger multifaceted "dome-shaped" islands, up to 25 nm high and 80-150 nm wide. Finally, the largest islands that form are square-based truncated pyramids with a very narrow size distribution, ≈ 50 nm high and ≈ 250 nm wide. The pyramidal islands normally seen in the intermediate size range (≈ 150 nm) are not observed. The small lens-shaped islands appear to be defect free, while some of the multifaceted islands as well as all the large truncated pyramids contain misfit dislocations. The existence of multifaceted islands, in the size range where pyramids have previously been reported and of truncated pyramids in the size range where multifaceted "dome-shaped" islands have previously been reported, is attributed to the high growth rate used. Furthermore, under the growth conditions used, the truncated-pyramid-shaped islands are characterized by a very narrow size distribution.