Spontaneous Alloy Composition Ordering in GaAs-AlGaAs Core鈥揝hell Nanowires

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• 作者：Daniel Rudolph ; Stefan Funk ; Markus D枚blinger ; Stefanie Mork枚tter ; Simon Hertenberger ; Lucas Schweickert ; Jonathan Becker ; Sonja Matich ; Max Bichler ; Dan膲e Spirkoska ; Ilaria Zardo ; Jonathan J. Finley ; Gerhard Abstreiter ; Gregor Koblm眉ller
• 刊名：Nano Letters
• 出版年：2013
• 出版时间：April 10, 2013
• 年：2013
• 卷：13
• 期：4
• 页码：1522-1527
• 全文大小：318K
• 年卷期：v.13,no.4(April 10, 2013)
• ISSN：1530-6992

文摘

By employing various high-resolution metrology techniques we directly probe the material composition profile within GaAs鈥揂l_0.3Ga_0.7As core鈥搒hell nanowires grown by molecular beam epitaxy on silicon. Micro Raman measurements performed along the entire (>10 渭m) length of the 111-oriented nanowires reveal excellent average compositional homogeneity of the nominally Al_0.3Ga_0.7As 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 10³-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鈥?0 meV below the band gap of Al_0.3Ga_0.7As. These features are attributed to deep level defects under influence of the observed local alloy fluctuations in the shell.

Keywords:

Core鈭抯hell nanowires; GaAs; AlGaAs; molecular beam epitaxy; composition; segregation