Directed self‐assembly of single quantum dots for telecommunication wavelength optical devices

Abstract

Strong confinement of charges in few electron systems such as in atoms, molecules and quantum dots leads to a spectrum of discrete energy levels that are often shared by several degenerate quantum states. Since the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum in the Coulomb blockade regime, resulting from a change in cantilever resonance frequency and dissipation during tunneling events, shows one by one electron charging of a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the first observation of predicted temperature-dependent shifts of Coulomb blockade peaks. Further, by scanning the surface we observe that several quantum dots may reside on what topologically appears to be just one. These images of grouped weakly and strongly coupled dots allow us to estimate their relative coupling strengths.

Energy levels of few-electron quantum dots imaged and characterized by atomic force microscopy

“…T he ability to confine single charges at discrete energy levels makes semiconductor quantum dots (QDs) promising candidates as a platform for quantum computation (1, 2) and singlephoton sources (3). Tremendous progress has been made not only in understanding the properties of single electrons in QDs but also in controlling their quantum states, which is an essential prerequisite for quantum computation (4).…”

Deterministic emitter-cavity coupling using a single-site controlled quantum dot

“…1͑a͒. Quantum dot site control is achieved through selective-area epitaxy 24 which is used to direct the self-assembly process in the InAs/ InP quantum dot material system. The fabrication process involves nucleation of a single InAs quantum dot at the apex of an InP pyramid as shown in the scanning electron microscopy ͑SEM͒ image in Fig.…”

Greenberger-Horne-Zeilinger states in a quantum dot molecule

“…4, involve U = 2, V = 0.1, t = 0.05, t ′ t, and V ′ V and a bias ǫ of the order of tunneling, t. The values currently available for lateral gated quantum dots on GaAs are in the required parameter ranges of U ∼ 2, V ∼ 0.1, and t ∼ 0.05 meV. By building quantum dot networks using individually gated self-assembled quantum dots on nanotemplates 29 one can envisage reaching values of parameters for self-assembled quantum dots U ∼ 20, V ∼ 10, t ∼ 10 meV which should lead to the exchange coupling reaching J ∼ 40 meV, exceeding room temperature.…”