Growth and Characterization of p-n Junction Core-Shell GaAs Nanowires on Carbon Nanotube Composite Films
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Growth and Characterization of p-n Junction Core-Shell GaAs Nanowires on Carbon Nanotube Composite Films Parsian K. Mohseni1, Gregor Lawson2, Alex Adronov2, and Ray R. LaPierre1 1
Centre for Emerging Device Technologies, Department of Engineering Physics, McMaster University, Hamilton, Ontario, L87 4L7, Canada
2
Department of Chemistry, McMaster University, Hamilton, Ontario, L87 4L7, Canada
ABSTRACT Thin films composed of poly(ethylene imine)-functionalized single-walled carbon nanotubes (CNTs) were formed through a vacuum filtration process and decorated with Au nanoparticles, roughly 40 nm in diameter. The Au nanoparticles, on the surface of the CNT fabric, accommodated the growth of GaAs nanowires (NWs), according to the vapour-liquidsolid (VLS) mechanism, in a gas-source molecular beam epitaxy (GS-MBE) system. Structural analysis indicated that the nanowires, up to 2.5 µm in length, were not preferentially oriented at specific angles with respect to the substrate surface. The NWs grew in the energetically favored [0001] direction of the wurtzite lattice while stacking faults, characterized as zincblende insertions, were observed along their lengths. Micro-photoluminescence spectroscopy demonstrated bulk-type optical behaviour. Current-voltage behaviour of the core-shell pnjunction heterostructured NWs exhibited asymmetric rectification. Thus, the potential for the incorporation of such hybrid NW/CNT architectures into an emerging class of flexible optoelectronic devices is demonstrated.
INTRODUCTION To date, semiconductor nanowires (NWs) and carbon nanotubes (CNTs) have been the focus of intensive research within the realm of nanometer scale science and engineering [1-2]. Of particular interest are CNT composite films that have been demonstrated as promising materials for flexible optoelectronics applications due to their impressive optical transparency and electrical conductivity [3-4]. Also, semiconductor nanowires, which can be grown on dissimilar surfaces [5] via the Au-assisted vapour-liquid-solid (VLS) mechanism, have been successfully incorporated as the active medium into novel NW-based light-emitting diodes and photovoltaic cells [6-7]. Here, we establish for the first time, hybrid III-V semiconductor NW/CNT-film architectures assembled through gas-source molecular beam epitaxy (GS-MBE). The nature of the growth surface is discussed in terms of the site specific nucleation of each nanowire. Characterization of the structural properties, optical quality, and electrical behaviour of the NWs grown on the CNT fabrics is presented. This work represents the initial step towards a novel class of flexible photonic devices, based on hybrid NW/CNT architectures.
EXPERIMENTAL DETAILS Single-walled CNTs were covalently functionalized with poly(ethylene imine) (PEI), and formed into 1-2 µm thick films via a vacuum filtration technique [8]. Au nanoparticles, roughly 40 nm in diameter, were reduced on the CNT film surface by submerging the film in an HAuCl4 solution for 60 seconds. The Au decorat
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