Optical and thermal properties of Ge₂Sb₂Te₅, Sb₂Se₃, and Sb₂S₃ for reconfigurable photonic devices [Invited]

Abstract

Phase change materials (PCMs) are one of the most promising materials candidates for reconfigurable optics owing to their two solid-state atomic structures that render distinct optical properties. Recently, there have been growing interests in integrating these materials into photonic devices for achieving reconfigurable optical properties. In this paper, we focus on examining the optical and thermal properties of three essential phase change materials: Ge 2 Sb 2 Te 5 , Sb 2 Se 3 , and Sb 2 S 3 . The latter two have been specifically tailored for photonic applications, with minimal absorption losses in the near-infrared spectrum. In particular, we report the optical constants, refractive index (n) and extinction coefficient (k), for 300 nm thick Ge 2 Sb 2 Te 5 , Sb 2 Se 3 , and Sb 2 S 3 on CaF 2 substrate across a wide spectral range of 0.3 μ m to 40 μ m in amorphous and crystalline states. We observe that while Ge 2 Sb 2 Te 5 exhibits a larger contrast in the index of refraction upon phase transformation compared to the other two compositions, Sb 2 Se 3 and Sb 2 S 3 demonstrate a substantial reduction in their extinction coefficients within the infrared spectrum. In addition, using time-domain thermoreflectance (TDTR), we report their thermal conductivity as a function of temperature up to 320°C. According to our observation, the room temperature thermal conductivity of Sb 2 Se 3 and Sb 2 S 3 increases by almost a factor of four upon phase transformation from amorphous to crystalline. The findings of this study provides necessary parameters for modeling PCM based photonic devices and emphasize the strong potential of Sb 2 Se 3 and Sb 2 S 3 as promising material candidates for reconfigurable optics due to their low-loss transmission in infrared spectrum, paving the way for their practical implementation in future photonic devices.