11:00 AM - EQ18.03.02
InAs Nanowires on Nanomembranes—Growth and Device Aspects
Didem Dede1,Kristopher Cerveny2,Chunyi Huang3,Valerio Piazza1,Nicholas Morgan1,Martin Friedl1,Lucas Güniat1,Jean-Baptiste Leran1,Jaime Segura Ruiz4,Valentina Bonino4,Lincoln Lauhon3,Dominik Zumbuhl2,Anna Fontcuberta i Morral1
Ecole Polytechnique Federale de Lausanne1,Universität Basel2,Northwestern University3,European Synchrotron Radiation Facility4
Show Abstract
Even though many advances have been made in the field of quantum computing, Majorana fermions, the exotic mystery of topological qubits, have yet to be conclusively identified and are thus still waiting to be explored.[1] Materials science is still the bottleneck of this progress; high-quality semiconductor nanowires (NWs) in a precise configuration are required, as well as a deeper understanding of their structural, electrical, and transport properties. Previously, selective area growth of horizontal In-based NW networks by molecular beam epitaxy has been proposed for these systems due to the scalability of the process, inherent properties of the material, and the cleaner environment of the machine.[2,3]Growing NWs on defect-free GaAs templates or nanomembranes (NMs) results in high crystal quality, eliminating undesired impurity incorporation coming from the substrate. As a result, these NWs show field-effect gating, quantum coherence, and induced superconductivity.[3,4] Moreover, the carrier concentration of the In(Ga)As NW branches can be enhanced by quasi-remotely doping the (111)B GaAs NMs. This results in the observation of weak anti-localization, an indication of strong spin-orbit interaction (SOI), and enhanced coherence length and mean free path.[5] However, the maximum achievable In concentration on these NMs is 50%, and Si dopants accumulate at the NW/NM interface contributing to the donor interface scattering. Thus, advancements are still necessary to achieve the optimal material design for efficient quantum transport.
In this study, we address several challenges related to the design, growth, and exploitation of horizontal NWs grown epitaxially on NMs. First, we explore the crystal orientation of the GaAs substrate as a design parameter for changing the morphology of the In(Ga)As NWs. Since growths on (111)B, (100), and (110) are all governed by both thermodynamics and kinetics, the GaAs NMs have different morphologies and facets depending on the surface energy. Consequently, the NW geometry and the amount of In incorporation in the wire change depending on the substrate orientation. We demonstrate that growth on (100) substrates results in NWs that grow conformally around a low-aspect-ratio NM. These nanowires can be nearly pure InAs and exhibit only a narrow-intermixed region. For growth on (110) substrates, the NWs have a trapezoidal cross-section with a moderate In concentration. Subsequently, we explore the possibility to modify the morphology of the NMs by adding a small amount of Sb during the epitaxial growth (less than 5 at%). Sb acts as a “morphactant” in the system, favoring the formation of a flat top facet. This provides a smoother growth surface for the InAs NW, helping to decrease the scattering at the NM-NW interface. We also investigate new routes to suppress Si dopant diffusion in remotely-doped structures by two different approaches: (i) suppressing dopant mobility during the growth by decreasing the temperature and (ii) introducing a few-nm thick trapping layer after the doped layer growth. Dopant displacement was characterized by atom probe tomography. Finally, we investigate the magnetotransport properties of some of the quasi-remotely doped NWs. By fabricating a dual gated architecture at each side of the NW, we aim to keep carrier density constant while changing the electric field across two gates. This novel device design would make it possible to tune the SOI present in these NWs.
References
[1] P. Yu et al., Nat. Phys. 2021, 17, 482.
[2] M. Friedl et al.,Nano Lett. 2018, 18, 2666.
[3] F. Krizek et al.,Phys. Rev. Mater. 2018, 2, 093401.
[4] S. Vaitiekenas et al.,Phys. Rev. Lett. 2018, 121
[5] M. Friedl et al., Nano Lett. 2020, 20, 3577.
Acknowledgments: Funding from Swiss National Science Foundation, NCCR QSIT