Examination of InAs/InSb heterointerfaces in Nanowires

Antimony based semiconductor nanowires (NWs) have been widely studied in recent years due to their large spin-orbit coupling, high Landé g-factor, and single subband conductance. They may become a key material in the field of quantum information processing and are currently used in the search for Majorana fermions by electrical transport [1]. Theory predicts that Majorana bound states can be realized in a 1D semiconductor coupled to a superconductor when exposed to an external magnetic field and manipulated by electrostatic gates [2]. Using NWs as a mean to achieve this goal has become even more promising after a recent report on epitaxial semiconductor/superconductor NW interfaces [3,4]. InSb NWs are expected to be the optimal material in this endeavor as the large spin-orbit interaction, and the possibility to induce superconductivity, in InSb makes it feasible to drive the wires into the topologically protected regime [2,5]. Realization of Majorana bound states in semiconductor/superconductor NWs would open the route to perform quantum information processing in networks by exploiting the unique non-abelian braiding statistics and non-trivial fusion rules which are inherent in Majorana Fermions [6].

In this work we present a detailed investigation of the growth of Au-seeded InSb NWs grown by molecular beam epitaxy (MBE) on (111)B InAs substrate. As InSb has proven difficult to grow directly on InAs substrates, an InAs stem mediates the growth as seen in Fig. 1. In Fig. 2 the growth deformation in this region is analyzed using Geometric Phase Analysis (GPA) and the abrupt interface indicates that the compositional change occur rapidly. To explore the growth dynamics of InSb, the transition region between InAs/InSb is investigated in order to study how incorporation of Sb affects the system. This analysis is performed using HR-TEM, Dark-Field Electron Holography (DFEH) [7], and Energy Dispersive x-ray Spectroscopy (EDS). In Fig. 3 a DFEH image is obtained by interfering the diffracted beam from the InAs part of the NW with that from the InSb part. Using DFEH the in-plane deformation in the growth direction is shown in Fig. 4.  Comparing the results from the aforementioned techniques with parameters used in the MBE during growth gives insight into the incorporation dynamics of Sb in NWs. Understanding the dynamics of NW growth is crucial in order to optimize and utilize these in novel devices. InSb NWs with two-facet Al shell are also investigated to explore the epitaxy of the interface, since the interface plays the major role in utilizing InSb/Al heterostructures for topological superconductivity and devices.

References:

[1] Kitaev, A.Y., 2001. Unpaired Majorana fermions in quantum wires. Physics-Uspekhi, 44(10S), p.131.

[2] Leijnse, M. and Flensberg, K., 2012. Introduction to topological superconductivity and Majorana fermions. Semiconductor Science and Technology, 27(12), p.124003.

[3] Chang, W., Albrecht, S.M., Jespersen, T.S., Kuemmeth, F., Krogstrup, P., Nygård, J. and Marcus, C.M., 2015. Hard gap in epitaxial semiconductor–superconductor nanowires. Nature Nanotechnology, 10(3), pp.232-236.

[4] Krogstrup, P., Ziino, N.L.B., Chang, W., Albrecht, S.M., Madsen, M.H., Johnson, E., Nygård, J., Marcus, C.M. and Jespersen, T.S., 2015. Epitaxy of semiconductor–superconductor nanowires. Nature Materials, 14(4), pp.400-406.

[5] Mourik, V., Zuo, K., Frolov, S. M., Plissard, S. R., Bakkers, E. P. A. M., & Kouwenhoven, L. P. (2012). Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices. Science, 336(6084), 1003-1007.

[6] Alicea, J., Oreg, Y., Refael, G., von Oppen, F. and Fisher, M.P., 2011. Non-Abelian statistics and topological quantum information processing in 1D wire networks. Nature Physics, 7(5), pp.412-417.

[7] Hÿtch, M., Houdellier, F., Hüe, F. and Snoeck, E., 2008. Nanoscale holographic interferometry for strain measurements in electronic devices. Nature, 453(7198), pp.1086-1089.

Figures:

Figure 1 HR-TEM image of the transition region between InAs and InSb.

Figure 2 Geometric Phase Analysis of Fig. 1 showing the deformation of the lattice planes along the growth direction.

Figure 3 Darkfield holography image of the transition region with pure InSb as the reference region.

Figure 4 In-plane deformation along the growth direction obtained from DFEH.

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EMC Abstracts - https://emc-proceedings.com/abstract/examination-of-inasinsb-heterointerfaces-in-nanowires/