Phonons and excitons in ZrSe2–ZrS2 alloys. Issue 17 (1st April 2020)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Journal of materials chemistry. Volume 8:Issue 17(2020)
• Page Start: 5732
• Page End: 5743
• Publication Date: 2020-04-01
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d0tc00731e
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : We combine experimental and theoretical methods to understand the impact of long-range Coulomb interactions on phonons and excitons in ZrS x Se2− x . Abstract : 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 ZrS x Se2− 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 ZrS x Se2− 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 ZrS x Se2− 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 ZrS x Se2− x and lays the foundation for future applications of this material.