Pushing the Composition Limit of Anisotropic Ge_1–xSn_x Nanostructures and Determination of Their Thermal Stability

Abstract

Ge 1−x Sn x nanorods (NRs) with a nominal Sn content of 28% have been prepared by a modified microwavebased approach at very low temperature (140 °C) with Sn as growth promoter. The observation of a Sn-enriched region at the nucleation site of NRs and the presence of the low temperature -Sn phase even at elevated temperatures support a template-supported formation mechanism. The behaviour of two distinct Ge 1−x Sn x compositions with high Sn content of 17% and 28% upon thermal treatment has been studied and reveal segregation events occurring at elevated temperatures, but also demonstrate the temperature window of thermal stability. In situ transmission electron microscopy investigations revealed a diffusion of metallic Sn clusters through the Ge 1−x Sn x NRs associated with temperatures where the material composition changes drastically. These results are important for the explanation of distinct composition changes in Ge 1−x Sn x and the observation of solid diffusion combined with dissolution and redeposition of Ge 1−y Sn y (x>y) exhibiting a reduced Sn content. Absence of metallic Sn results in increased temperature stability by ~70 °C for Ge 0.72 Sn 28 NRs and ~60 °C for Ge 0.83 Sn 17 nanowires (NWs). In addition, a composition-dependent direct bandgap of the Ge 1−x Sn x NRs and NWs with different composition is illustrated using Tauc plots. ASSOCIATED CONTENT Supporting Information. Additional SEM, TEM, EDX and XRD data are provided. Moreover, a video for the phase separation in the TEM is supplied. This material is available free of charge via the Internet at http://pubs.acs.org.

Solution-based low-temperature synthesis of germanium nanorods and nanowires

“…Shifts of reflections in the XRD pattern should not be expected due to the similarity in size of Ga and Ge [35]. Similar to the observation of the unusually high Ga content in the here presented Ge NRs, low-temperature synthesis methods and kinetic process control can lead to the formation of metastable alloys with considerable metal incorporation in the Ge matrix, such as the Ge–Sn alloy [36–38] or efficient Bi incorporation in Ge nanocrystals [39]. The incorporation of the impurity dopants in the actual lattice should be investigated in detail using single-crystalline material and accumulation at twin planes should be excluded [40].…”

Influence of growth kinetics on Sn incorporation in direct band gap Ge1−xSnx nanowires

“…xSnx nanowires have been previously reported via both top-down fabrication 13,14 and bottom-up growth. [15][16][17] However, the etch chemistry required to fabricate highly crystalline, uniform top-down Ge1-xSnx nanowires is, as of yet, still in its infancy, and bottom-up grown nanowires often exhibit low aspect ratios and non-uniform morphologies, with bending and kinking, thus restricting efficient light emission from these materials. 15 Taking account of the lack of optically efficient group IV alloy nanomaterials, we have recently reported the fabrication of direct bandgap Ge1-xSnx nanowires with up to 9.2 at.…”

Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19nanowires

“… 29 – 33 Besides a large body of data related to the thin film growth on single crystalline substrates and significant recent advancements in this field, 17 , 22 , 34 – 36 the number of reports on one-dimensional nanostructures and nanoparticles with significant Sn incorporation is still very limited. 37 Top-down approaches based on the post-growth etching of epitaxial films to prepare desired morphologies have been applied 38 and a few reports describing suitable bottom-up approaches for a reliable formation of Ge 1– x Sn x nanoparticles 39 – 43 and one-dimensional nanostructures 44 – 50 are available. Morphological control to obtain shape anisotropic single crystalline materials has been achieved using Ge NWs as templates in order to obtain core–shell Ge/Ge 1– x Sn x NWs 45 but also non-templated metal-seed supported growth of Ge 1– x Sn x NWs via gas-phase 46 , 47 and solution-based synthesis 44 , 48 , 49 has been described in literature.…”

“… 37 Top-down approaches based on the post-growth etching of epitaxial films to prepare desired morphologies have been applied 38 and a few reports describing suitable bottom-up approaches for a reliable formation of Ge 1– x Sn x nanoparticles 39 – 43 and one-dimensional nanostructures 44 – 50 are available. Morphological control to obtain shape anisotropic single crystalline materials has been achieved using Ge NWs as templates in order to obtain core–shell Ge/Ge 1– x Sn x NWs 45 but also non-templated metal-seed supported growth of Ge 1– x Sn x NWs via gas-phase 46 , 47 and solution-based synthesis 44 , 48 , 49 has been described in literature. To date, anisotropic Ge 1– x Sn x nanostructures usually are in the range of 9–13 at% Sn, 45 , 46 while our microwave-based synthesis procedures gives access to highly crystalline material with very high Sn content of 17–32 at%.…”