Jun 27, 2012
Seed particles govern nanowire growth and properties
Researchers from MIT, led by Silvija Gradečak, have demonstrated that the choice of metal particles for seeding nanowire growth is critical to achieving the desired dimensions, density and structural quality for future devices, such as high-efficiency LEDs.
In the study, metal seed layers (gold and nickel) of different thicknesses were deposited onto a substrate via electron beam evaporation prior to growth. The films de-wet on the surface to form localized seeds at elevated temperatures, and act as preferential nucleation sites for GaN nanowires. The rate of nucleation events and probability of defect formation is governed by the supersaturation and surface energies of the seeds.
The team found that gold-seeded GaN nanowires grow slower compared with nickel-seeded ones, and also contain 2D defects that are seldom found in nickel-seeded GaN nanowires. The optical properties of the final material were also observed to differ as a result of the nanowire growth rate and substrate effects. These phenomena are all closely tied to the fraction of gallium atoms in the seed particles during nanowire growth.
Full details can be found in the journal Nanotechnology.
About the author
This study was conducted in the lab for Nanophotonics and Electronics at MIT, supervised by Silvija Gradečak, Thomas Lord associate professor of Materials Science and Engineering. The lead author, Xiang Zhou, is a PhD candidate supported by the Center for Excitonics, an Energy Frontier Research Center funded by the US Department of Energy. Jordan Chesin and Samuel Crawford are also PhD candidates in the Gradečak group. All three of them are working on developing GaN-based nanowires for energy-related applications including LEDs for solid-state lighting and photovoltaic applications.