| AVS 64th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology Division | Thursday Sessions |
| Session NS+AS+EM+MI+SP+SS-ThM |
| Session: | Nanoscale Imaging and Characterization |
| Presenter: | Anders Mikkelsen, Lund University, Sweden |
| Authors: | J. Knutsson, Lund University, Sweden M. Hjort, Lund University, Sweden P. Kratzer, University Duisburg-Essen, Germany J. Webb, Lund University, Sweden S. Lehmann, Lund University, Sweden K.D. Thelander, Lund University, Sweden C.J. Palmstrom, UCSB R. Timm, Lund University, Sweden A. Mikkelsen, Lund University, Sweden |
| Correspondent: | Click to Email |
Despite the many III-V nanowire (NW) technologies under current development, be it solar cells and light emitting diodes or high speed/low power electronics, there are still only few studies of their surfaces. The atomic scale structure and morphology of NW surfaces are however central in determining their functionality, due to the inherently large surface to bulk ratio. In addition, III-V NWs can be tailored with segments of both the cubic zinc blende (ZB) and hexagonal wurtzite (WZ) structures and in a variety of materials combinations. This allow experimental access to nanocrystallite surfaces and interfaces not found in the bulk. We have demonstrated atomically resolved Scanning Tunneling Microscopy/Spectroscopy (STM/S) on a wide variety of these III-V NWs and on operational NW devices [1-5]. We now use these methods for studying atomic scale surface structural changes and impact on local electronic properties on both GaAs and InAs NWs at room temperature and at 5K.
We explore the surface diffusion and alloying of Sb into GaAs NWs with controlled axial stacking of Wz and Zb crystal phases. We find that Sb preferentially incorporates into the surface layer of the -terminated Zb segments rather than the -terminated Wz segments. Density functional theory calculations verify the higher surface incorporation rate into the Zb phase and find that it is related to differences in the energy barrier of the Sb-for-As exchange reaction on the two surfaces. These findings demonstrate a simple processing-free route to compositional engineering at the monolayer level along NWs.
Using low temperature STM/S we measure local density of states of atomic scale tailored Zb segments in Wz InAs nanowires down to the smallest possible crystal lattice change. We find that Zb crystal phase signatures can be seen in the density of states both on the conduction and valence band sides as well as in the band positions down to the smallest possible Zb segment. Additionally we find indications of confined state effects due to the difference in bandgap between Wz and Zb. Finally we explore the stability of InAs NWs with atomic scale STM during the application of voltages through the NWs in a device configuration. We observe that applying realistic voltages to InAs NWs results in removal of atomic scale defects and smoothening of the morphology.
[1] E. Hilner et al., Nano Letters, 8 (2008) 3978; M. Hjort et al., ACS Nano 6, 9679 (2012)
[2] M. Hjort et al., Nano Letters, 13, 4492 (2013)
[3] M. Hjort et al., ACS Nano, 8 (2014) 12346
[4] J. L. Webb, et al Nano Letters 15 (2015) 4865
[5] J. L. Webb et al., Nano Research, 7 (2014) 877
[6] O. Persson et al., Nano Letters 15 (2015) 3684