title: Aluminum-Induced photoluminescence red shifts in core-shell GaAs/Al(x)Ga(1-x)As nanowires.
abstract: We report a new phenomenon related to Al-induced carrier confinement at the interface in core-shell GaAs/Al(x)Ga(1-x)As nanowires grown using metal-organic vapor phase epitaxy with Au as catalyst. All Al(x)Ga(1-x)As shells strongly passivated the GaAs nanowires, but surprisingly the peak photoluminescence (PL) position and the intensity from the core were found to be a strong function of Al composition in the shell at low temperatures. Large and systematic red shifts of up to ~66 nm and broadening in the PL emission from the GaAs core were observed when the Al composition in the shell exceeded 3%. On the contrary, the phenomenon was observed to be considerably weaker at the room temperature. Cross-sectional transmission electron microscopy reveals Al segregation in the shell along six Al-rich radial bands displaying a 3-fold symmetry. Time-resolved PL measurements suggest the presence of indirect electron-hole transitions at the interface at higher Al composition. We discuss all possibilities including a simple shell-core-shell model using simulations where the density of interface traps increases with the Al content, thus creating a strong local electron confinement. The carrier confinement at the interface is most likely related to Al inhomogeneity and/or Al-induced traps. Our results suggest that a low Al composition in the shell is desirable in order to achieve ideal passivation in GaAs nanowires.
authors.affiliation: Department of Micro- and Nanosciences, Micronova, Aalto University, Aalto, Finland. veer.dhaka@aalto.fi
authors.forename: Veer
authors.initials: V
authors.lastname: Dhaka
authors.forename: Jani
authors.initials: J
authors.lastname: Oksanen
authors.forename: Hua
authors.initials: H
authors.lastname: Jiang
authors.forename: Tuomas
authors.initials: T
authors.lastname: Haggren
authors.forename: Antti
authors.initials: A
authors.lastname: Nykänen
authors.forename: Reza
authors.initials: R
authors.lastname: Sanatinia
authors.forename: Joona-Pekko
authors.initials: JP
authors.lastname: Kakko
authors.forename: Teppo
authors.initials: T
authors.lastname: Huhtio
authors.forename: Marco
authors.initials: M
authors.lastname: Mattila
authors.forename: Janne
authors.initials: J
authors.lastname: Ruokolainen
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Anand
authors.forename: Esko
authors.initials: E
authors.lastname: Kauppinen
authors.forename: Harri
authors.initials: H
authors.lastname: Lipsanen