Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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What Ga droplets can and cannot do in the growth of GaAs nanowires on SiTauchnitz, T.; Balaghi, L.; Hübner, R.; Bischoff, L.; Schneider, H.; Helm, M.; Dimakis, E.
The central role of liquid Ga droplets in the self-catalyzed growth of free-standing GaAs nanowires on Si(111) substrates will be overviewed, including our recent findings. Initially, Ga droplets interact with the surface oxide layer that typically covers a Si substrate and create nanoholes. The nucleation of GaAs nanowires takes place there, in direct contact with the underlying Si. Using a sequence of Ga deposition and substrate annealing steps, the number density of nanowires can be controlled from 107 to 109 cm-2 without the need for pre-patterned substrates. During the growth of nanowires, the Ga droplet on their apex captures Ga adatoms and As4 molecules efficiently and, thus, enhances the local growth rate in favor of the axial elongation of the nanowires. The contact angle of the droplet with the underlying nanowire determines the phase of the growing crystal. Long segments of pure zinc blende phase are possible, whereas wurtzite has been demonstrated only for short segments. On the other hand, Ga-catalyzed growth has certain inherent limitations. Those concern the axial growth of ternary alloys, the abruptness of axial hetero-interfaces and the ability for defect-free interruptions of the axial growth. Most of those limitations are related to the solubility properties of other elements (i.e. In, Al, As) in Ga droplets. As a method of probing and controlling the growth processes inside the droplets, the droplet-confined alternate pulsed epitaxy is introduced.
Invited lecture (Conferences)
19th European Workshop on Molecular Beam Epitaxy, 19.-22.03.2017, Korobitsyno, St. Petersburg, Russia
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