Palladium seeded GaAs nanowires
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Maria E. Messing Solid State Physics, Lund University, 221 00 Lund, Sweden; and Synchrotron Radiation Research, Lund University, 211 00, Lund, Sweden
Kimberly A. Dick Solid State Physics, Lund University, 221 00 Lund, Sweden; and Centre for Analysis and Synthesis, Lund University, 221 00 Lund, Sweden (Received 15 June 2015; accepted 11 December 2015)
In this work, we present a detailed investigation of the growth of palladium-seeded GaAs nanowires. Nanowires grown on GaAs (111)B substrates consist of three different morphologies, denoted as curly (containing multiple kinks), inclined (relative to the substrate, such as Æ001æ), and vertical. We show that the relative yield of the different types is controllable by a combination of V/III ratio and temperature, where vertical and inclined nanowires are promoted by a high temperature and low V/III ratio. These growth conditions are expected to promote a higher Ga incorporation into the Pd particle, which is confirmed by energy dispersive x-ray analysis. We propose that the observed relationship between particle composition and nanowire morphology may be related to the particle phase, with liquid particles promoting straight nanowire growth. In addition, particles at the tips of nanowires are sometimes observed to be smaller than the initial particle size, suggesting that Pd has been lost during the growth process. Finally, we demonstrate the importance of initial particle size-control to interpret diameter changes after growth.
I. INTRODUCTION
Gold nanoparticles are extensively used for seeding growth of III–V semiconductor nanowires, as they are known to yield uniform nanowire morphology over a large range of process conditions.1 However, gold is well known to have a high diffusivity in silicon and to deteriorate its electrical properties by introducing mid-gap states,2 complicating integration of III–V nanowires into Si-based devices. In addition, the most favorable growth direction for gold-seeded III–V nanowires is Æ111æ B, while the Æ001æ direction would be preferable for integration with Si electronics. Finally, gold-seeded nanowires grown in the Æ111æ B direction have a strong tendency to form stacking faults,3 which are also detrimental to the electronic properties.4,5 For these reasons it is of great interest to explore gold-free growth techniques, for example using alternative metal seed particles. Pd and Fe have for example been shown to initiate the growth of nanowires in other preferential directions, including Æ110æ,6,7 Æ111æ A,8,9 and Æ001æ,7 in some cases without any stacking faults. In addition to defect-free zinc blende, more exotic polytypes, such as 4H, have been observed for example in Cu-seeded Contributing Editor: Joan M. Redwing a) Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2015.400 J. Mater. Res., Vol. 31, No. 2, Jan 28, 2016
nanowires.10 Finally, intentional incorporation of atoms from the seed particle can potentially be used to t
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