Elucidating the Degradation Mechanisms in Silicon Telluride through Multimodal Characterization

Silicon telluride (Si2Te3) and many other tellurium-containing compounds show emergent Raman peaks located at ∼120 and ∼140 cm–1 as they age. The origin of these two emergent peaks is controversial in the literature and has been attributed to myriad causes such as the intrinsic Raman modes of the telluride materials, surface oxidation, defects, double resonances, and tellurium precipitates. The controversial nature of these peaks has led to the misidentification of highly degraded materials as pristine and to the misinterpretation of changes in Raman spectra. Here, we present a comprehensive and multimodal study on Si2Te3 thin films and bulk crystals grown by a chemical vapor deposition process. We find that the two emergent Raman peaks originate from tellurium nanocrystallites formed in the degraded surface layers of Si2Te3. The formation of the tellurium nanocrystallites is shown to be a result of a hydrolysis process in which Si2Te3 reacts with atmospheric water vapor. This study unambiguously clarifies the origin of the controversial Raman peaks seen in numerous telluride compounds and provides a blueprint for the accurate characterization of these material systems in the future.