  We report a combined experimental and computational study of the optical
properties of individual silicon telluride (Si2Te3) nanoplates. The p-type
semiconductor Si2Te3 has a unique layered crystal structure with hexagonal
closed-packed Te sublattices and Si-Si dimers occupying octahedral
intercalation sites. The orientation of the silicon dimers leads to unique
optical and electronic properties. Two-dimensional Si2Te3 nanoplates with
thicknesses of hundreds of nanometers and lateral sizes of tens of micrometers
are synthesized by a chemical vapor deposition technique. At temperatures below
150 K, the Si2Te3 nanoplates exhibit a direct band structure with a band gap
energy of 2.394 eV at 7 K and an estimated free exciton binding energy of 150
meV. Polarized reflection measurements at different temperatures show
anisotropy in the absorption coefficient due to an anisotropic orientation of
the silicon dimers, which is in excellent agreement with theoretical
calculations of the dielectric functions. Polarized Raman measurements of
single Si2Te3 nanoplates at different temperatures reveal various vibrational
modes, which agree with density functional perturbation theory calculations.
The unique structural and optical properties of nanostructured Si2Te3 hold
great potential applications in optoelectronics and chemical sensing.
