Hierarchical Self-Assembly of Lateral Quantum-Dot Molecules Around Nanoholes

Abstract

Quantum dots (QDs) can be fabricated as inclusions of a narrow energyband- gap semiconductor in a matrix of larger band gap material. In QDs, charge carriers are confined in all directions, and they are hence referred to as artificial atoms. One of the most elegant and convenient approaches to produce QDs is to exploit the Stranski–Krastanow (SK) growth mode during lattice-mismatched heteroepitaxial growth. The availability of such a simple fabrication method has rendered it possible to study the properties of selfassembled QDs in great detail [1–3].

In contrast to single QDs, relatively little work has been done up to now on coupled QD systems, i.e., on artificial molecules [4–7]. QD molecules are interesting, both as a new playground for studying interacting electronic systems and for their potential application as building blocks of quantum information processing devices [8]. In fact, single QDs can be used as one [9, 10] or two “qubit” [11] systems, but cannot be scaled to perform complex operations. For this purpose, chains or groups of QDs are required. However, the fabrication of QD molecules by self-assembly is more complex than the growth of single QDs, since a single self-assembly step rarely leads to welldefined groups of spatially close QDs, which possibly behave as QD molecules. A relatively simple way to fabricate vertical QD molecules is to grow stacks of QDs.