Developing new processes and applications
The nitride semiconductors (InN, GaN, AlN) are different from the ordinary III/V compounds in that the thermodynamic bulk structure of all of them is hexagonal, as compared to the other cubic III-V semiconductors. They also demand higher growth temperatures, and can readily be grown without seed particles. However, the band gap of these materials are in general larger, giving light emission in the UV-Blue region. There is promise of having very efficient LED:s based on these materials, ranging over the whole visible region by combinations of different nitrides, but to achieve this, the problem of avoiding threading dislocations due to the lattice mismatch at the interfaces have to be resolved.
Selected area growth, where small perfect nuclei can be grown from small holes in a mask, is one way of generating perfect single crystals, and by combinations of kinetic and thermodynamic growth, specific facets can be enhanced to show pyramidal, wire-like or prismatic nanostructures, giving varying application areas.
Aerotaxy: large-scale, gas-phase nanowire synthesis
Aerotaxy is a new method for growing semiconductor nanowires without involving a substrate, which we are trying to develop into a scalable process for mass production of designed nanowire materials. In short, Aerotaxy works by creating an aerosol of catalytic seed particles and adding precursor molecules in a tube furnace, which causes nanowires to grow at a very high speed of more then 1 µm/s, which is 100 – 1000 times faster than the substrate-based methods. The nanowires can be collected in filters, directly on substrates or dispersed in liquids. The nanowires are being studied using scanning and transmission electron microscopy, photoluminescence, scanning tunnelling microscopy, and with electrical transport.
The origin of the technology is due to a unique combination of aerosol and nanowire science, and builds on early work on aerosol synthesis of semiconductor nanoparticles. The fundamental motivation for the research is to reach a better understanding of the intrinsic mechanisms of nanowire growth, without a substrate being involved. The practical motivation is that nanowires show great potential for applications in solar cells, light emitting diodes, batteries or nanoelectronics.
Continuous gas-phase synthesis of nanowires with tunable properties.M. Heurlin, M. H. Magnusson, D. Lindgren, M. Ek, L. R. Wallenberg, K. Deppert, and L. Samuelson, Nature, 2012, 492: 90. DOI: 10.1038/nature11652
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High In-content InGaN nano-pyramids: tuning crystal homogeneity by optimized nucleation of GaN seeds. Zhaoxia Bi, Anders Gustafsson, Filip Lenrick, David Lindgren, Olof Hultin, L. Reine Wallenberg, B. Jonas Ohlsson, Bo Monemar and Lars Samuelson. J. of Applied Physics 123 (2), (2018) 025102. DOI: 10.1063/1.5010237
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GaAsP Nanowires Grown by Aerotaxy. Metaferia, Wondwosen; Persson, Axel R.; Mergenthaler, Kilian; Yang, Fangfang; Zhang, Wei; Yartsev, Arkady; Wallenberg, Reine; Pistol, Mats-Erik; Deppert, Knut; Samuelson, Lars; Magnusson, Martin H. NANO Letters 16:9 ( 2016) 5701-5707. DOI: 10.1021/acs.nanolett.6b02367
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