Colloidal Synthesis of Homogeneous Ge1-x-y Si y Sn x Nanoalloys with Composition-Tunable Visible to Near-IR Optical Properties

Group IV alloy nanocrystals (NCs) are a class of direct energy gap semiconductors that show high elemental abundance, low to nontoxicity, and composition-tunable absorption and emission properties. These properties have distinguished Ge1-xSnx NCs as intriguing materials for near-infrared (IR) optical studies. Achieving a material with efficient visible emission requires a modified class of group IV alloys, and the computational studies suggest that this can be achieved with Ge1-x-ySiySnx NCs. Herein, we report a colloidal strategy for the synthesis of bulk-like (10.3 +/- 2.5-25.5 +/- 5.3 nm) and quantum-confined (3.2 +/- 0.6-4.2 +/- 1.1 nm) Ge1-x-ySiySnx alloys that show strong size confinement effects and composition-tunable visible to near IR absorption and emission properties. This synthesis produces a homogeneous alloy with a diamond cubic Ge structure and tunable Si (0.9-16.1%) and Sn (1.8-14.9%) compositions, exceeding the equilibrium solubility of Sn (<1%) in crystalline Si and Ge. Raman spectra of Ge1-x-ySiySnx alloys show a prominent red-shift of the Ge-Ge peak and the emergence of a Ge-Si peak with increasing Si/Sn, suggesting the growth of homogeneous alloys. The smaller Ge1-x-ySiySnx NCs exhibit absorption onsets from 1.21 to 1.94 eV for x = 1.8-6.8% and y = 0.9-16.1% compositions, which are blue-shifted from those reported for Ge1-x-ySiySnx bulk alloy films and Ge1-xSnx alloy NCs, indicating the influence of Si incorporation and strong size confinement effects. Solid-state photoluminescence (PL) spectra reveal core-related PL maxima from 1.77-1.97 eV in agreement with absorption onsets, consistent with the energy gaps calculated for similar to 3-4 nm alloy NCs. With a facile, low-temperature solution synthesis and direct control over physical properties, this methodology presents a noteworthy advancement in the synthesis of bulk-like and quantum-confined Ge1-x-ySiySnx alloys as versatile materials for future optical and electronic studies.

Automated summary

Group IV alloy nanocrystals are direct energy gap semiconductors with high elemental abundance, low toxicity, and composition-tunable absorption and emission properties. In this study, a colloidal strategy for the synthesis of Ge1-x-ySiySnx alloys with strong size confinement effects and composition-tunable properties was reported.