Eutectic-Bismuth Indium as a Growth Solvent for the Electrochemical Liquid-Liquid-Solid Deposition of Germanium Microwires and Coiled Nanowires

• Published in: Crystal growth & design 2018-02, Vol.18 (2), p.677-685
• Main Authors: DeMuth, Joshua, Ma, Luyao, Lancaster, Mitchell, Acharya, Saurabh, Cheek, Quintin, Maldonado, Stephen
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.7b01036

Crystalline germanium (Ge) micro- and nanowires have been grown from aqueous electrolytes through an electrochemical liquid-liquid-solid (ec-LLS) process using eutectic bismuth indium (e-BiIn) alloy as the liquid metal electrode. This alloy represents the first non-Hg or non-Ga containing liquid metal to be used for the growth of a group IV semiconductor crystal below the boiling point of water. The electrochemical stability of e-BiIn in aqueous electrolyte was assessed through cyclic voltammetry, which showed the metal alloy was destabilized either by anodic oxidation at potentials more positive than −1.0 V vs E(Ag/AgCl) or by cathodic reduction of Bi to BiH3 at potentials more negative than −1.4 V vs E(Ag/AgCl). Within this potential window, ec-LLS produced Ge micro- and nanowires that were evaluated with scanning electron microscopy, high resolution transmission electron microscopy, and selected area electron diffraction. The cumulative analyses showed pronounced crystallinity in the as-prepared Ge microwires and nanowires, with nanowires showing an unexpected coiled morphology. Atom probe tomography data showed some incorporation of In and Bi at 6 and 3 at. %, respectively. The tomography data further demonstrated that the distribution of the metals was not uniform, as In-rich clusters were observed. A high doping character in the as-prepared Ge nanowires was separately confirmed with two-terminal resistivity measurements. In total, this work not only identifies a new liquid metal type that is amenable for ec-LLS but also suggests strongly that the composition of the liquid metal influences the resultant crystal size, shape, and purity.