Growth of In-Plane Ge_1–xSn_x Nanowires with 22 at. % Sn Using a Solid–Liquid–Solid Mechanism

Abstract

Germanium−tin alloys have gained strong attention because of their optical and electrical properties and their compatibility with silicon-based technologies. By increasing the Sn content in the alloy, the charge carrier mobility can be improved, and the energy band gap can be transformed from indirect to direct. However, the fabrication of GeSn is a huge challenge as the equilibrium solubility of Sn in Ge is limited to <1 at. %. The aim of this study is the fabrication of in-plane GeSn nanowires catalyzed by Sn nanoparticles to overcome this limit. Transmission electron microscopy-based analysis shows that the in-plane GeSn nanowires can reach an out-of-equilibrium Sn concentration of 22 at. %. Moreover, a homogenous incorporation of Sn into the Ge nanowires is achieved during the in-plane solid−liquid−solid growth process, without Sn segregation or precipitation in the host material. The results are discussed in the framework of three kinetic-based models: the step growth model, the continuous growth model, and the dimer-insertion model, to account for the nonclassical physical aspects behind the extraordinary catalyst incorporation.

Facile synthesis of Ge1−xSnx nanowires

“…For practical applications in optoelectronic and electric devices, the thermal stability of Ge 1−x Sn x material is a crucial property which has been widely studied and reported [17,23,24,[41][42][43][44][45]. Zaumseil et al showed that the tin segregation temperature of Ge 1−x Sn x alloys increases with decreasing Sn content, and that Ge 0.91 Sn 0.09 was stable at temperatures up to 400°C [17].…”

“…Ge 1−x Sn x alloys are commonly fabricated using ion implantation, laser melting [4,5,19], molecular beam epitaxy (MBE) [7], and chemical-vapor deposition(CVD) approaches [6,[20][21][22]. Apart from these thin film based preparations, there are limited reports of the synthesis of anisotropic Ge 1−x Sn x nanostructures by top-down and bottom-up approaches [12,[23][24][25][26][27][28].…”

“…The most established synthetic approaches, for group IV nanowires (such as Ge and Ge 1−x Sn x ), involve the use of metal growth-promoters in bottom-up processes such as: vapour-liquid-solid (VLS), vapor-solid-solid (VSS), In-plane-solid-liquid-solid (IP-SLS), supercritical fluid-liquid-solid (SFLS) and solution-liquid-solid (SLS) mechanisms. [12,18,23,26,27,29]. Amongst these, the SLS approach offers benefits such as low equipment cost, high scalability, mild-reaction conditions, easy control, and access to non-flammable germanium precursors (such as triphenylchlorogermane) [30].…”

“…In order to fabricate Ge 1−x Sn x nanowires incorporating high tin content, non-equilibrium introduction of tin into the germanium lattice has been proposed and demonstrated by several groups. These used either a VLS mechanism from liquid-injection CVD upon Au [18] or AuAg catalysts [12,26], or IPSLS approach [23,27]. However, reports focused on self-seeded SLS growth of high quality Ge 1−x Sn x nanowires from tin catalyst are rare.…”

The Theoretical Optical Gain of Ge1−xSnx Nanowires

“…As we know, incorporating tin ( α ‐Sn) into Ge material has been proved to be an effective method to engineer the bandgap of the indirect L ‐valley and direct Γ‐valley, and similar to direct‐band‐gap III–V or II–VI group semiconductor compounds, GeSn alloys can be integrated into photonic circuits and used as light emitter, which consists of only group IV elements. Recently, apart from the bulk GeSn alloys, many experimental researchers also focused on low‐dimensional GeSn‐related systems, such as GeSn quantum dots (QDs), nanowires (NWs) or core‐shell nanowires, and quantum wells (QWs) . In these experiments, GeSn or straind GeSn related low‐dimensional structures with Sn fraction larger than 10% have been realized, and especially GeSn NWs with very high Sn content, namely 22% and 30%, have also been reported.…”