Improved Surface Passivation of Colloidal Ge_1–xSn_x Nanoalloys through Amorphous SiO₂ Shell Growth

Abstract

Ge1– x Sn x alloy nanocrystals (NCs) are a class of semiconductors that show interesting (photo)­physical properties such as composition-dependent visible to near-IR energy gaps and enhanced light–matter interactions compared to single element Ge NCs. With decreasing size and increasing Sn content, the molar absorptivity and emission efficiency increase, making these NCs attractive for optoelectronic, molecular imaging, and sensing studies. To further improve the optical stability, there is a need to passivate the Ge1– x Sn x surface with a robust shell material to protect the core from oxidation and inhibit chemical exchange when exposed to extreme environments. Herein, we report a fluent synthetic method for the growth of a thin silica layer on bulk-like (14.9 ± 1.7 nm) and quantum-confined (4.4 ± 0.6 nm) Ge1– x Sn x NCs. Physical characterization of Ge1– x Sn x /SiO2 core/shell NCs suggests that the diamond cubic structure of the core is retained upon shell growth, whereas solid-state and solution-state absorption spectra confirm the composition-dependent energy gap tunability. The core–shell NCs (1.23–2.07 eV for x = 0.03–0.09) show an average energy gap increase of 0.38 eV relative to the core NCs (0.91–1.67 eV for x = 0.03–0.09) owing to minor surface etching induced by shell growth. Surface analysis of core–shell NCs suggests a notable decrease in Ge2+ species and greater dominance of Ge0 species relative to the organically passivated Ge1– x Sn x core NCs, confirming the production of robust, oxidation-resistant, and optically stable Ge1– x Sn x /SiO2 alloy NCs.

Colloidal Synthesis of Homogeneous Ge1–x–ySiySnx Nanoalloys with Composition-Tunable Visible to Near-IR Optical Properties

“…The smaller QDs exhibit composition-tunable absorption onsets and emission maxima from 1.21−1.94 and 1.77−1.97 eV for x = 1.8−6.8% and y = 0.9−16.1% compositions, respectively. These transition energies are significantly higher than those reported for GeSiSn thin films and ∼3−5 nm Ge 1−x Sn x alloy QDs, 35 signifying the effects of Si incorporation and strong size confinement effects. This constitutes an expansion of the optical properties that can be achieved for group IV alloy NCs.…”

Toward White Light Random Lasing Emission Based on Strained Nano Polygermanium Doped with Tin via Metal-Induced Crystallization (MIC)

“…Figure shows the existence of GeSn peaks (JCPDS File Card No. 01-089-5011) with different orientations in different planes: (111) at 2θ = 27.5°, and (311) at 2θ = 62.5°. , A Ge(220) peak is observed at 2θ = 46° in the sample of the second configuration (Al/Ge/Sn/Ge/Sn), and this peak disappeared in the first configuration (Al/Si/Sn/Ge/Sn), since the second configuration is rich with germanium …”

Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization

“…29 These together with the controlled technological processes ensuring reduced Ge oxidation, and NCs/QDs/NPs surface passivation, size control and improved functionality lead to demonstrating the potential of Ge-based NCs/QDs/NPs for optoelectronic and photovoltaic devices, e.g., in photodetectors 20,30 and photoMOSFETs for monolithically integrated Si optical interconnects, 31 for light harvesting and solar energy conversion in solar cells 28,32−34 or as bioimaging fluorescence probes in biomedical applications. 35,36 Extensive research has been done on Ge NCs/QDs/NPs embedded in dielectric matrices (SiO 2 , TiO 2 , HfO 2 , Si 3 N 4 , Al 2 O 3 ), the matrix playing the role in passivation of the NCs surface. Remarkable effects and performances such as multiple exciton generation effect 37 and high photodetector internal quantum efficiency (IQE) over 100% at room temperature (RT) 38,39 were evidenced in films formed of Ge QDs/NCs/NPs in oxides (mostly SiO 2 ) usually deposited by magnetron sputtering.…”

“…These are possible by tailoring and engineering QDs/NCs/NPs size, − density, composition, , strain, interface with embedding matrix, and shape, by employing core–shell nanostructures , and by doping . These together with the controlled technological processes ensuring reduced Ge oxidation, and NCs/QDs/NPs surface passivation, size control and improved functionality lead to demonstrating the potential of Ge-based NCs/QDs/NPs for optoelectronic and photovoltaic devices, e.g., in photodetectors , and photoMOSFETs for monolithically integrated Si optical interconnects, for light harvesting and solar energy conversion in solar cells ,− or as bioimaging fluorescence probes in biomedical applications. , …”