Evidence for Structural Phase Transitions Induced by the Triple Phase Line Shift in Self-Catalyzed GaAs Nanowires

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• 作者：Xuezhe Yu ; Hailong Wang ; Jun Lu ; Jianhua Zhao ; Jennifer Misuraca ; Peng Xiong ; Stephan von Moln谩r
• 刊名：Nano Letters
• 出版年：2012
• 出版时间：October 10, 2012
• 年：2012
• 卷：12
• 期：10
• 页码：5436-5442
• 全文大小：455K
• 年卷期：v.12,no.10(October 10, 2012)
• ISSN：1530-6992

文摘

Self-catalyzed growth of GaAs nanowires are widely ascribed to the vapor鈥搇iquid鈥搒olid (VLS) mechanism due to the presence of Ga particles at the nanowire tips. Here we report synthesis of self-catalyzed GaAs nanowires by molecular-beam epitaxy covering a large growth parameter space. By carefully controlling the Ga flux and its ratio with the As flux, GaAs nanowires without Ga particles and exhibiting a flat growth front are produced. Using scanning electron microscopy and high-resolution transmission electron microscopy, we compare the growth rate and structure, especially near the growth front, of the nanowires with and without Ga droplets. We find that regardless of whether Ga droplets are present on top, the nanowires have a short wurtzite section following the zinc-blende bulk structure. The nanowires without Ga droplets are terminated by a thin zinc-blende cap, while the nanowires with Ga droplets do not have such a cap. The bulk zinc-blende phase is attributed to the Ga droplet wetting the sidewall during growth, pinning the triple phase line on the sidewall. The zinc-blend/wurtzite/(zinc-blende) phase transitions at the end of growth are fully consistent with the triple phase line shifting up to the growth front due to the progressive consumption of the Ga in the droplet by crystallization with As. The results imply an identical VLS growth mechanism for both types of GaAs NWs, and their intricate structures provide detailed comparison with and specific experimental verification of the recently proposed growth mechanism for self-catalyzed III鈥揤 semiconductor nanowires ( Phy. Rev. Lett. 2011, 106, 125505). Using this mechanism as a guideline, we successfully demonstrated controllable fabrication of two distinct types of axial superlattice GaAs NWs consisting of zinc-blende/defect-section and wurtzite/defect-section units.

Keywords:

Molecular-beam epitaxy; semiconductor nanowires; nanowire growth kinetics; structural transition of nanowires