title: Droplet etching of deep nanoholes for filling with self-aligned complex quantum structures.
abstract: Strain-free epitaxial quantum dots (QDs) are fabricated by a combination of Al local droplet etching (LDE) of nanoholes in AlGaAs surfaces and subsequent hole filling with GaAs. The whole process is performed in a conventional molecular beam epitaxy (MBE) chamber. Autocorrelation measurements establish single-photon emission from LDE QDs with a very small correlation function g ((2))(0)≃ 0.01 of the exciton emission. Here, we focus on the influence of the initial hole depth on the QD optical properties with the goal to create deep holes suited for filling with more complex nanostructures like quantum dot molecules (QDM). The depth of droplet etched nanoholes is controlled by the droplet material coverage and the process temperature, where a higher coverage or temperature yields deeper holes. The requirements of high quantum dot uniformity and narrow luminescence linewidth, which are often found in applications, set limits to the process temperature. At high temperatures, the hole depths become inhomogeneous and the linewidth rapidly increases beyond 640 °C. With the present process technique, we identify an upper limit of 40-nm hole depth if the linewidth has to remain below 100 μeV. Furthermore, we study the exciton fine-structure splitting which is increased from 4.6 μeV in 15-nm-deep to 7.9 μeV in 35-nm-deep holes. As an example for the functionalization of deep nanoholes, self-aligned vertically stacked GaAs QD pairs are fabricated by filling of holes with 35 nm depth. Exciton peaks from stacked dots show linewidths below 100 μeV which is close to that from single QDs.
authors.affiliation: Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany. akuester@physnet.uni-hamburg.de.
authors.forename: Achim
authors.initials: A
authors.lastname: Küster
authors.affiliation: Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Heyn
authors.affiliation: Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany.
authors.forename: Arne
authors.initials: A
authors.lastname: Ungeheuer
authors.affiliation: Tyndall National Institute, University College Cork, Lee Maltings Dyke Parade, Cork, T12R5CP, Ireland.
authors.forename: Gediminas
authors.initials: G
authors.lastname: Juska
authors.affiliation: Tyndall National Institute, University College Cork, Lee Maltings Dyke Parade, Cork, T12R5CP, Ireland.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tommaso Moroni
authors.affiliation: Tyndall National Institute, University College Cork, Lee Maltings Dyke Parade, Cork, T12R5CP, Ireland.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Pelucchi
authors.affiliation: Institut für Nanostruktur- und Festkörperphysik, Center for Hybrid Nanostructures (CHYN), Universität Hamburg, Jungiusstraße 11, Hamburg, 20355, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hansen
keywords: Droplet etching; Nanostructuring; Quantum dot; Self-assembly; Semiconductor