We report on the formation of clusters of self-assembled quantum dots (termed quantum-dot molecules). Each cluster, typically consisting of four closely spaced SiGe islands, is formed by preferential nucleation around the edges of square pits. Uniform-sized pits are directly formed by controlled deposition of Si and C on the initial Si(100) surface, followed by the growth of a thin Si buffer layer. Formation of $\{105\}$ pit walls as precursors to island formation and elastic relaxation effects near the pits appear to influence island nucleation. Quantum-dot molecules may have potential applications in nanoelectronic devices and may exhibit novel electronic and optical properties.

• Received 22 April 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.1473