Growth behavior and microstructure of Ge self-assembled islands on nanometer-scale patterned Si substrate

We investigate the growth behavior and microstructure of Ge self-assembled islands of nanometer dimension on Si (0 0 1) substrate patterned with hexagonally ordered holes of ∼25 nm depth, ∼30 nm diameter, and ∼7×1010 cm−2 density. At 9 Å Ge coverage and 650 °C growth temperature, Ge islands preferentially nucleate inside the holes, starting at the bottom perimeter. Approximately 14% of the holes are filled by Ge islands. Moiré fringe analysis reveals partial strain relaxation of about 72% on average, which is not uniform even within a single island. Crystalline defects such as dislocation are observed from islands smaller than 30 nm. Increased Ge coverage to 70 Å forms larger aggregates of many interconnected islands with slightly increased filling factor of about 17% of the holes. Reducing the growth temperature to 280 °C results in much higher density of islands with a filling factor of about 80% and with some aggregates. The results described in this report represent a potential approach for fabricating semiconductor quantum dots via epitaxy with higher than 1010 cm−2 density.