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S1.06 - Straight and Vertically Aligned Palladium-Seeded GaAs Nanowires 
April 7, 2015   9:45am - 10:00am

The use of a foreign metal seed particle as a catalyst for nanowire growth is an established technique used to achieve growth for a wide range of growth temperature and precursor flows. The predominantly used material is gold and it is well known that it is suitable over a wide range of growth parameters. It enables growth of nanowires with a well-controlled diameter and length; in addition, it is possible to grow heterostructures and switch crystal structure. We are currently investigating the use of alternative seed particle materials to learn more about how the seed-particle affects the properties of the nanowire, such as its morphology, structure and growth mechanism. We will present our current findings of palladium seeded GaAs, where we have done a systematic study over a large growth parameter window. The palladium particles were generated by an aerosol-phase deposition using a spark discharge generator (SDG), able to generate pristine spherical particles of metals with a high dose and size control. A closed coupled showerhead MOCVD from AIXTRON was used to grow the nanowires.The explored parameter space is, growth temperature 350-600�C, V/III ratio 0.1-73, growth time 5-30 minutes, particle size, 10-40 nm and particle dose in the range of 1-10 ?m-2. The analysis is performed by high-resolution transmission electron microscopy (HREM), energy dispersive x-ray spectroscopy (XEDS) and scanning electron microscopy (SEM). We will demonstrate how to grow vertically aligned wires. In addition, we will also demonstrate how the growth parameters affect typical growth characteristics such as nucleation, crystal structure, crystal growth direction, morphology and growth rate. Other groups have succeeded in growing straight wires in non-(111)B directions for InAs [1]�[3]. However, this is the first time that epitaxial (111)B GaAs nanowires seeded by palladium are reported. The XEDS analysis reveals that the gallium content in the seed particle after growth can be between 45-80 at%. High gallium content may allow for vapor-liquid-solid (VLS) growth at higher growth temperatures and is suspected to be the key to the epitaxial (111)B wires. This and other interesting discoveries will be discussed, such as how the particle composition is affected by growth parameters and how the palladium seeded growth compares to gold seeded growth. References [1] H. Xu, Y. Wang, Y. Guo, Z. Liao, and Q. Gao, �Defect-free< 110> zinc-blende structured InAs nanowires catalyzed by palladium,� Nano Lett., pp. 5744�5749, 2012. [2] S. Heun, B. Radha, and D. Ercolani, �Pd-assisted growth of InAs nanowires,� Cryst. Growth �, vol. 10, no. 9, pp. 4197�4202, Sep. 2010. [3] R. Perumal, Z. Cui, P. Gille, J.-C. Harmand, and K. Yoh, �Palladium assisted hetroepitaxial growth of an InAs nanowire by molecular beam epitaxy,� Semicond. Sci. Technol., vol. 29, no. 11, p. 115005, Nov. 2014.

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