Robust Material Properties in Epitaxial In$_2$Te$_3$ Thin Films Across Varying Thicknesses

Abstract

Sesqui-chalcogenides serve as a critical bridge between traditional semiconductors and quantum materials, offering significant potential in applications such as thermoelectrics, phase change memory, and topological insulators. While considerable attention has been focused on antimony- and bismuth-based compounds, characterized by substantial property changes upon reduction in film thickness, indium containing sesqui-chalcogenides like In$_2$Te$_3$ are emerging as promising candidates for photovoltaics and electronic devices. However, the effects of film thickness on the properties of In$_2$Te$_3$ remain largely unexplored. In this study, we investigate high-quality In$_2$Te$_3$ thin films grown by molecular beam epitaxy on Si(111) substrates across a thickness range from 2.7 nm to 24 nm. We employ X-ray diffraction, reflective high-energy electron diffraction and atomic force microscopy to analyze both the crystal structure and film morphology. Additionally, we utilize broadband optical spectroscopy alongside femtosecond pump-probe measurements and Raman spectroscopy to assess optical and vibrational properties, respectively. Our analysis reveals that material properties exhibit minimal dependence on film thickness, contrasting sharply with behavior observed in other chalcogenides such as Sb$_2$Te$_3$, Bi$_2$Se$_3$, or GeTe. This phenomenon can be attributed to covalent bonding present in In$_2$Te$_3$, which differs from those in its antimony- and bismuth-containing counterparts.