Anomalous Raman Modes in Tellurides

TL;DR

This paper investigates the origin of broad anomalous Raman bands in tellurides, attributing them to nanoscale or microscale clusters of trigonal Te and Se precipitates, enhancing understanding of chalcogenide materials.

Contribution

It demonstrates that the anomalous Raman modes in tellurides are due to Te and Se precipitates, providing a unified explanation for these features across various chalcogenides.

Findings

Anomalous bands are caused by Te and Se precipitates.

Laser heating influences Te segregation.

Provides a general framework for Raman characterization of chalcogenides.

Abstract

Two broad bands are usually found in the Raman spectrum of many Te-based chalcogenides, which include binary compounds, like ZnTe, CdTe, HgTe, GaTe, GeTe, SnTe, PbTe, GeTe2, As2Te3, Sb2Te3, Bi2Te3, NiTe2, IrTe2, TiTe2, as well as ternary compounds, like GaGeTe, SnSb2Te4, SnBi2Te4, and GeSb2Te5. Many different explanations have been proposed in the literature for the origin of these two anomalous broad bands in tellurides, usually located between 119 and 145 cm-1. They have been attributed to the own sample, to oxidation, to the folding of Brillouin-edge modes onto the zone center, to the existence of a double resonance, like that of graphene, or to the formation of Te precipitates. In this paper, we provide arguments to demonstrate that such bands correspond to clusters or precipitates of trigonal Te in form of nanosize or microsize grains or layers that are segregated either inside or at the surface of the samples. Several mechanisms for Te segregation are discussed and sample heating caused by excessive laser power during Raman scattering measurements is emphasized. Finally, we show that anomalous Raman modes related to Se precipitates also occur in selenides, thus providing a general vision for a better characterization of selenides and tellurides by means of Raman scattering measurements and for a better understanding of chalcogenides in general.