title: Spontaneous alloy composition ordering in GaAs-AlGaAs core-shell nanowires.
abstract: By employing various high-resolution metrology techniques we directly probe the material composition profile within GaAs-Al0.3Ga0.7As core-shell nanowires grown by molecular beam epitaxy on silicon. Micro Raman measurements performed along the entire (>10 μm) length of the [111]-oriented nanowires reveal excellent average compositional homogeneity of the nominally Al0.3Ga0.7As shell. In strong contrast, along the radial direction cross-sectional scanning transmission electron microscopy and associated chemical analysis reveal rich structure in the AlGaAs alloy composition due to interface segregation, nanofaceting, and local alloy fluctuations. Most strikingly, we observe a 6-fold Al-rich substructure along the corners of the hexagonal AlGaAs shell where the Al-content is up to x ~ 0.6, a factor of 2 larger than the body of the AlGaAs shell. This is associated with facet-dependent capillarity diffusion due to the nonplanarity of shell growth. A modulation of the Al-content is also found along the radial [110] growth directions of the AlGaAs shell. Besides the ~10(3)-fold enhancement of the photoluminescence yield due to inhibition of nonradiative surface recombination, the AlGaAs shell gives rise to a broadened band of sharp-line luminescence features extending ~150-30 meV below the band gap of Al0.3Ga0.7As. These features are attributed to deep level defects under influence of the observed local alloy fluctuations in the shell.
authors.affiliation: Walter Schottky Institut, Physik Department, Technische Universität München, Garching, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rudolph
authors.forename: Stefan
authors.initials: S
authors.lastname: Funk
authors.forename: Markus
authors.initials: M
authors.lastname: Döblinger
authors.forename: Stefanie
authors.initials: S
authors.lastname: Morkötter
authors.forename: Simon
authors.initials: S
authors.lastname: Hertenberger
authors.forename: Lucas
authors.initials: L
authors.lastname: Schweickert
authors.forename: Jonathan
authors.initials: J
authors.lastname: Becker
authors.forename: Sonja
authors.initials: S
authors.lastname: Matich
authors.forename: Max
authors.initials: M
authors.lastname: Bichler
authors.forename: Danĉe
authors.initials: D
authors.lastname: Spirkoska
authors.forename: Ilaria
authors.initials: I
authors.lastname: Zardo
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Finley
authors.forename: Gerhard
authors.initials: G
authors.lastname: Abstreiter
authors.forename: Gregor
authors.initials: G
authors.lastname: Koblmüller
mesh_terms: D000497:Alloys / Q000737:chemistry*; D001152:Arsenicals / Q000737:chemistry*; D003460:Crystallization; D005708:Gallium / Q000737:chemistry*; D049449:Luminescence; D049329:Nanostructures / Q000737:chemistry; D053770:Nanowires / Q000737:chemistry*; D010316:Particle Size; D012825:Silicon / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000497:Alloys; D001152:Arsenicals; C043055:gallium arsenide; D005708:Gallium; D012825:Silicon