Interfacial properties of self-assembled GaN nanowires on pre-processed Al₂O₃(0001) surfaces

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• 作者：T. Koukoula^a ; J. Kioseoglou^a ; ^{sifisl@auth.gr" class="auth_mail" title="E-mail the corresponding author} ; Th. Kehagias^a ; F. Furtmayr^b ; M. Eickhoff^c ; H. Kirmse^d ; Th. Karakostas^a ; Ph. Komninou^a
• 关键词：High-resolution transmission electron microscopy (HRTEM) ; Quantitative HRTEM analysis ; Geometric phase analysis ; Sapphire substrate ; GaN Nanowires ; Catalyst-free growth
• 刊名：Materials Science in Semiconductor Processing
• 出版年：2016
• 出版时间：15 November 2016
• 年：2016
• 卷：55
• 期：Complete
• 页码：46-50
• 全文大小：1745 K

文摘

Surface treatment of the foreign substrate is a critical factor influencing heteroepitaxial catalyst-free growth of nanowires, their crystal quality, their diameter and their areal density. To this end, catalyst-free growth of GaN nanowires on Al₂O₃(0001) by plasma-assisted molecular beam epitaxy was achieved using the following substrate surface treatments: (a) deposition of a Si_xN_y layer on nitridated Al₂O₃ surface, and (b) deposition of Si on bare Al₂O₃ surface. The nanostructure of GaN nanowires and GaN/Al₂O₃ interfaces was explored by quantitative high-resolution transmission electron microscopy and related analytical methods. Spontaneous growth of GaN nanowires was realized on the amorphous Si_xN_y layer, while a discontinuous crystalline zone in contact with Al₂O₃ was identified as partially strained AlN. Subsequently, GaN nanowires were directly grown on top of Al₂O₃ among stress-free Si islands. The orientation relation of these islands with the substrate was the [112](ge" height="11" width="15" alt="View the MathML source" style="margin-top: -5px; vertical-align: middle" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S1369800116300622-si0009.gif">$\overline{1}\overline{1}1$)Si//[ge" height="11" width="21" alt="View the MathML source" style="margin-top: -5px; vertical-align: middle" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S1369800116300622-si0010.gif">$1\overline{1}00$](0001)Al₂O₃, providing the minimum lattice misfit between the two structures. Increasing the Si deposition time a higher density of Si islands was realized, leading to non-coalesced nanowires of lower density and better structural quality. Hence, the presence of Si islands induced a mask-like effect on the nucleation of GaN nanowires that can be exploited for a controlled catalyst-free growth of nanowires.