Engineered large area fabrication of ordered InGaAs-GaAs nanotube arrays
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Engineered large area fabrication of ordered InGaAs-GaAs nanotube arrays Ik Su Chun1, Varun B Verma2, and Xiuling Li1,2 1 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801 2 Department of Electrical and Computer Engineering, University of Illinois at UrbanaChampaign, Urbana, IL, 61801 ABSTRACT Strain induced self-rolling semiconductor nanotubes (SNTs) and related structures represent a new class of building blocks of nanotechnology. They are formed when strained planar bilayers are released from a substrate by selectively removing a sacrificial layer. The top down fabrication approach, compatible with conventional semiconductor processing technology, allows engineered placement of SNTs. In this article, we demonstrate the engineered large area fabrication of ordered InGaAs/GaAs nanotube arrays. In addition, we systematically investigate the crystal orientation dependence of the rolling direction by using a wheel configuration. Other aspects of the fabrication process and their effects on array uniformity are also discussed. INTRODUCTION Since the discovery of carbon nanotubes (CNTs) by Iijima et al. in 1991 [1], the breadth of research activities in this field has been extraordinary. CNTs’ perfect molecular structure and their distinct physical, electronic, and mechanical properties have led to potential applications in many fields including nanoelectronic devices for memory storage, interconnects, and biomedical sensing [2-7]. CNTs are formed by bottom-up methods such as chemical vapor deposition [811], vapor liquid solid growth [12], arc discharge [1], and laser ablation [13]. Group III-V compound semiconductor nanotubes (SNTs), a new paradigm, are formed by an entirely different process, a top down approach. They Tensile were first fabricated by Prinz et al. from Russia in 2000, Compressive using strain induced self-rolling of semiconductor M bilayers grown by molecular beam epitaxy [14]. The Undercut same group introduced SiGe self-rolled nanotubes [15]. The basic concept of the rolling mechanism of SNTs is illustrated in Figure 1. There are two essential components in strain induced self-rolling structures: (1) a sacrificial layer that can be selectively etched off from Figure 1. Illustration of the formation the substrate and epitaxial layers above; and (2) a mechanism of strain induced self-rolling strained bilayer consisting of two different materials of compound semiconductor nanotube. (e.g. InAs/GaAs) or single material with regions of different strains [16]. When the strained layer is undercut by selective etching, the compressively strained layer (e.g. InAs) deforms to expand with force F1 as labeled, while the relatively tensile strained layer (e.g. GaAs) on top resists the expansion with force F2. This results in a momentum M which drives the rolling action of the bilayer. SNTs formed this way have also been named RUNT for Rolled-Up NanoTubes (RUNTs) [17].
The strain induced formation mechanism has also been generalized to for
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