title: Laser Level Scheme of Self-Interstitials in Epitaxial Ge Dots Encapsulated in Si.
abstract: Recently, it was shown that lasing from epitaxial Ge quantum dots (QDs) on Si substrates can be obtained if they are partially amorphized by Ge ion bombardment (GIB). Here, we present a model for the microscopic origin of the radiative transitions leading to enhanced photoluminescence (PL) from such GIB-QDs. We provide an energy level scheme for GIB-QDs in a crystalline Si matrix that is based on atomistic modeling with Monte Carlo (MC) analysis and density functional theory (DFT). The level scheme is consistent with a broad variety of PL experiments performed on as-grown and annealed GIB-QDs. Our results show that an extended point defect consisting of a split-[110] self-interstitial surrounded by a distorted crystal lattice of about 45 atoms leads to electronic states at the Γ-point of the Brillouin zone well below the conduction band minimum of crystalline Ge. Such defects in Ge QDs allow direct transitions of electrons localized at the split-interstitial with holes confined in the Ge QD. We identify the relevant growth and annealing parameters that will let GIB-QDs be employed as an efficient laser active medium.
authors.affiliation: Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenberger Strasse 69, A-4040 Linz, Austria.
authors.forename: Martyna
authors.initials: M
authors.lastname: Grydlik
authors.affiliation: Department of Physics, Colorado School of Mines , Golden, Colorado 80401, United States.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Lusk
authors.affiliation: Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenberger Strasse 69, A-4040 Linz, Austria.
authors.forename: Florian
authors.initials: F
authors.lastname: Hackl
authors.affiliation: CNISM and Department of Physics, Sapienza Università di Roma , Piazzale A. Moro 2, 00185 Roma, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Polimeni
authors.affiliation: Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenberger Strasse 69, A-4040 Linz, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Fromherz
authors.affiliation: Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenberger Strasse 69, A-4040 Linz, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jantsch
authors.affiliation: Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenberger Strasse 69, A-4040 Linz, Austria.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Schäffler
authors.affiliation: Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz , Altenberger Strasse 69, A-4040 Linz, Austria.
authors.forename: Moritz
authors.initials: M
authors.lastname: Brehm
keywords: Silicon photonics; defect engineering; density functional theory; photoluminescence spectroscopy; quantum dots