| AVS 62nd International Symposium & Exhibition | |
| Materials Characterization in the Semiconductor Industry Focus Topic | Tuesday Sessions |
| Session MC-TuP |
| Session: | Materials Characterization in the Semiconductor Industry Poster Session (All areas) |
| Presenter: | Sofie Yngman, Lund University, Sweden |
| Authors: | S. Yngman, Lund University, Sweden S. McKibbin, Lund University, Sweden J. Knutsson, Lund University, Sweden F. Yang, Lund University, Sweden E. Lundgren, Lund University, Sweden M. Magnusson, Lund University, Sweden R. Timm, Lund University, Sweden A. Mikkelsen, Lund University, Sweden |
| Correspondent: | Click to Email |
III-V semiconductor nanowires (NWs) continue to show promising results as components in energy saving devices. GaAs NW arrays recently beat the record for photovoltaic solar cells presenting a conversion efficiency of 15.3% [1]. Given the large surface to volume ratio of NWs, performance in such devices may be strongly determined by surface characteristics for example, morphology, the presence of various oxide species and surface structure. We study GaAs NWs grown by using the novel growth technique aerotaxy [2]. In aerotaxy growth the NWs are catalyzed from Au aerosol nanoparticles floating freely in a continuous N2 flow mixed with group III and V precursor gases. The growth rate of NWs using aerotaxy is much faster than for epitaxially grown NWs and the absence of expensive crystal substrate allows large scale economic production. A detailed understanding of the surface properties of these aerotaxy NWs is highly relevant in order to optimize device performance.
We compare surface structure and morphology of GaAs aerotaxy NWs to GaAs NWs grown epitaxially on a substrate. We obtain images of the NWs from microns to the atomic scale using both Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM). Comparing this to chemical information obtained via X-ray Photoemission Spectroscopy (XPS) we find that the different growth techniques results in NWs with very different morphology. Using in air AFM phase measurements we show that the aerotaxy NWs exhibit a rounder cross section with few or no large facets in comparison to the hexagonal geometry of epitaxially grown NWs. XPS measurements show that by annealing the NWs in the presence of atomic hydrogen, we can remove the native oxides which form on them when exposed to air as previously observed for the expitaxially grown NWs[3][4]. From the XPS studies we can identify the different oxides present in the aerotaxy NWs before cleaning. We examine clean NWs using STM in Ultra High Vacuum. The morphology of the NWs is similar to as what is found in the AFM studies, however by direct atomic resolved imaging we can identify that even the round shaped aerotaxy NWs contain a considerable fraction of small unreconstructed patches of the {110} surface.
[1] http://www.solvoltaics.com/news.shtml (2015-05-01).
[2] M. Heurlin, et al. “Continuous gas-phase synthesis of nanowires with tunable properties”, Nature 492, 90-94 (2012).
[3] E. Hilner, et al. “Direct atomic scale imaging of III-V nanowire surfaces”, Nano Letters 8, 3978 (2008).
[4] M. Hjort, et al. “Direct imaging of atomic scale structure and electronic properties of GaAs wurtzite and zinc blende nanowire surfaces”, Nano Letters 13, 4492 (2013).