Growth of Ge Nanowires by Chemical Vapor Deposition at Atmospheric Pressure Using Readily Available Precursors GeO 2 and
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https://doi.org/10.1007/s11837-020-04401-3 Ó 2020 The Minerals, Metals & Materials Society
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Growth of Ge Nanowires by Chemical Vapor Deposition at Atmospheric Pressure Using Readily Available Precursors GeO2 and C2H5OH M. CUMBUL ALTAY
1,2
and S. EROGLU1,3
1.—Department of Metallurgical and Materials Engineering, Istanbul University – Cerrahpasa Engineering Faculty, Avcılar 34320, Istanbul, Turkey. 2.—e-mail: [email protected]. 3.—e-mail: [email protected]
The aim of the present study is to investigate chemical vapor deposition of Ge nanowires from readily available precursors solid GeO2 and liquid ethanol (C2H5OH) at atmospheric pressure. Gaseous GeO was generated in situ by the reactions between the reactants in the source temperature range from 1000 K to 1200 K. Ge wires were grown from the gaseous species transported from the source to the Au-coated Si substrate heated to 723 K for 5 min and 15 min. The diameter of the Ge wires slightly increased with increasing source temperature for the growth time of 5 min. The mean diameter ( 220 nm) of the wires grown from the species generated at 1200 K for 15 min was greater than those of the other samples (range 120 nm to 145 nm) owing to excessive Ge deposition on previously formed Ge wires. The growth of the Ge nanowires is discussed in terms of the vapor–liquid–solid mechanism and the reduction reactions between the species derived from the precursors.
INTRODUCTION One-dimensional nanostructures such as nanotubes and nanowires can be used as basic building blocks for bottom-up fabrication of nanoelectronics. Ge exhibits attractive properties such as high dielectric constant, low resistivity, and high electron and hole mobility (with a bandgap of 0.66 eV at 300 K).1 Ge in nanowire form is a promising semiconductor material for use in electronic, optoelectronic, and energy applications including batteries,2 field-effect transistors,3 field emitters,4 and photodetectors.5 Ge nanowires have been grown on metal catalystdecorated single-crystal substrates heated to above the eutectic temperature of the catalyst–Ge system by numerous techniques such as molecular beam epitaxy, hydrothermal processing, laser ablation, and chemical vapor deposition (CVD). Ge wires have been grown by the molecular beam epitaxy technique from Ge evaporated in high vacuum.6 The growth of Ge wires by the hydrothermal method is (Received June 7, 2020; accepted September 22, 2020)
conducted in water mixed with Ge and GeO2 at high pressures (e.g., 3.5 MPa) in an autoclave.7 It is commonly accepted that catalyzed Ge wire growth occurs via the vapor–liquid–solid (VLS) mechanism, which was originally proposed for Si in a CVD reactor from a gaseous mixture of SiCl4 and H2.8 Au catalyst is often used for Ge wire synthesis because it forms a eutectic liquid phase with Ge at 633 K9 and the liquid phase has a low vapor pressure and good wetting at the growth temperatures.10 The CVD technique is most commonly used to produce Ge nanowires because of its advant
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