Phonons and excitons in ZrSe₂-ZrS₂ alloys

Zirconium disulfide (ZrS2) and zirconium diselenide (ZrSe2) are promising materials for future optoelectronics due to indirect band gaps in the visible and near-infrared (NIR) spectral regions. Alloying these materials to produce ZrSxSe2−x (x = 0…2) would provide continuous control over key optical and electronic parameters required for device engineering. Here, we present a comprehensive analysis of the phonons and excitons in ZrSxSe2−x using low-temperature Raman spectroscopy and room-temperature spectroscopic ellipsometry (SE) measurements. We extract the Raman-active vibrational mode frequencies and find that they compare favorably with density functional theory (DFT) calculations. Our simulations and polarization-resolved measurements demonstrate that substitutional doping renders infrared (IR) modes to be Raman-active. This leads to a Raman spectrum dominated by nominally IR phonons, a phenomenon that originates from the large ionicity of the ZrSxSe2−x bonds. SE measurements of the complex refractive index quantify the blue-shift of direct, allowed exciton transitions with increasing S content, and we find strong light–matter interactions with low optical loss in the NIR. Correlating these data with DFT allows for an estimation of the Γ-point exciton binding energy at room temperature. This study illustrates the large effects of alloying on ZrSxSe2−x and lays the foundation for future applications of this material.

Oliver Sean M., Fox Joshua J., Hashemi Arsalan, Singh Akshay, Cavalero Randal L., Yee Sam, Snyder David W., Jaramillo R., Komsa Hannu-Pekka, Vora Patrick M.

A1 Journal article – refereed

Oliver, S. M., Fox, J. J., Hashemi, A., Singh, A., Cavalero, R. L., Yee, S., Snyder, D. W., Jaramillo, R., Komsa, H.-P., & Vora, P. M. (2020). Phonons and excitons in ZrSe2–ZrS2 alloys. Journal of Materials Chemistry C, 8(17), 5732–5743.