0D band gap engineering by MBE quantum rings: Fabrication and optical properties

Abstract

The partial capping technique has played a key role in the engineering of 0D nanostructures with tailor made properties (Michler et al. in Science 290(5500): 2282, 2000; Kiravittaya et al. in Rep. Prog. Phys. 72(4):046502, 2009). For example, it has allowed to fabricate a single-photon source that is based on a single self assembled quantum nanostructure embedded in a high-quality factor microcavity structure (Michler et al. in Science 290(5500):2282, 2000). Another example is the possibility to engineer what has been called “the smallest rings of electricity” (see Chap. 2), which unveil novel magnetic properties associated to non-trivial topologies at the nanoscale (Fomin (ed.) in J. Nanoelectron. Optoelectron., vol. 6. American Scientific, 2011) (see Chaps. 2, 4, 14, 17, and 18). In this chapter we show how it is possible to modify the shape and size of InAs on GaAs self assembled quantum dots grown by Molecular Beam Epitaxy (MBE) by introducing a pause during the capping process, also known as partial overgrowth technique (García et al. in Appl. Phys. Lett. 71:2014, 1997; Appl. Phys. Lett. 72:3172, 1998; Granados and García in Appl. Phys. Lett. 82:2401, 2003). Under certain growth-pause capping conditions it is possible to obtain self-assembled quantum rings. The changes in shape and size lead to a modification of the quantum confinement potential and enables the control over fundamental physical properties, such as the optical emission energy from ground or excited states, the magnitude of its fine structure splitting or the sign of its permanent electric dipole moment.