Interface Strains in 1D and 2D Si/Ge Structures for Quantum Computing

During the last decade great efforts were put in the development of materials for quantum computing for its outstanding properties such as high speed, large store capacity and low power consumption [1]. Silicon is the preferred platform for microelectronics infrastructures due to its scalability, low economic costs, harmless for the environment, established fabrication processes and easy implementation of advanced engineering techniques [2,3]. Moreover, silicon is a good quantum material due to its long coherence time of spins of localized electrons and efficient controllability [4]. Germanium is a semiconductor material compatible with silicon. Material engineering of Si-Ge in form of epitaxial planar heterostructures or nanowires lead to enhanced mobility properties for quantum purposes. Despite, strains arising from the 4% mismatch between Ge and Si lattice parameter create defects, these defects hinder mobility. With the purpose to achieve higher mobility, scattering must be minimized by diminishing strains and interface roughness. In this regard, an effective tool to evaluate strains and interface roughness is electron microscopy combined with Raman spectroscopy which allows structural and chemical characterization of samples at the nanoscale.<br/>In this work, we growth by chemical vapor deposition (CVD) 2D and 1D structures: (i) planar heterostructure’s composed with variable percentage of Si/Ge barrier’s and a Ge QW; and (ii) Ge-Si core-shell nanowires for quantum computing purposes. In a first step we chemically and structurally localized the Ge and Si by energy-dispersive X-ray (EDX) spectroscopy and scanning transmission electron microscopy (STEM) techniques. Finally, we aim to study strain of the Ge QW and core-shell interfaces by means of geometric phase analysis (GPA) and µ-Raman spectroscopy. High-resolution transmission electron microscope (HR-TEM) images of the samples were performed in a Jeol JEM F200 cFEG TEM/STEM to evaluate roughness of interfaces and defects. GPA is a microscopic technique by TEM based on the signal processing of HR-TEM images and its Fourier transform. For the µ-Raman measurements were performed at 633 nm wavelength in back scattering geometry with the help of a Horiba T64000 triple spectrometer and a liquid nitrogen-cooled CCD detector. The combination of both methods permits the control, calculation and mapping of strains in different directions (rotation xy, ε_xx, ε_xy and ε_yy) at high precision. By engineering the core-shell diameter ratio in 1D structures and Si_xGe_1-xcomposition of the barriers and Ge QW thicknesses in 2D structures, we proved and measured tensile/compressive strains in the interfaces between Ge QW and SiGe barriers and between core and shell NWs making our material suitable for integration in Si platforms for.quantum computing applications.<br/><br/><b>References</b><br/>[1] M. Hirvensalo,<i> Quantum computing.</i> Springer Science & Business Media, <b>2003</b>.<br/>[2] M.F. Gonzalez-Zalba, S. de Franceschi, E. Charbon, T. Meunier, M. Vinet, A. S. Dzurak, A. S., Nature Electronics,4(12), <b>2021</b>, 872-884.<br/>[3] R.Singh, M. M. Oprysko, D. Harame, Silicon germanium: technology, modeling, and design ,<b>2004.</b><br/>[4] A. M. Tyryshkin, S. A. Lyon, T. Schenkel, J. Bokor J. Chu, W. Jantsch, F. Schäffler J.L. Truitt, S. N. Coppersmith, M.A. Eriksson, Low-dimensional Systems and Nanostructures,<b> 2006, </b>35(2), 257-263.