In situ scanning tunneling microscopy study of C-induced Ge quantum dot formation on Si(100)

Deposition of submonolayer coverages of C on Si(100) prior to Ge growth leads to the formation of Ge quantum dots below the critical thickness for Ge islanding on bare Si(100). In situ scanning tunneling microscopy reveals a high density of irregularly shaped islands for Ge coverages from 2.5 to 4 ML. Island sizes are broadly distributed between 10 and 25 nm. Keeping the C coverage constant and increasing the Ge coverage from 2.5 to 4 ML, the islands increase in height but their density remains constant ${\text{(∼10}}^{11} {\mathrm{cm}}^{\mathrm{-2}}\mathrm{).}$ At a Ge coverage of 5.8 ML, formation of larger (105)-faceted islands is observed. Their density is reduced by a factor of 4 compared to smaller Ge coverages. Transmission electron microscopy shows that the nonfaceted islands are preserved after Si capping.