Development of Optical Phase Change Materials for Non-Volatile Photonics

Optical applications based on phase change materials (PCMs), that exhibit a significant change in optical properties upon an amorphous-crystalline structural phase transition, have attracted a lot of attention. For PCM-based nonvolatile optical applications, development of new optical PCM other than conventional Ge₂Sb₂Te₅ (GST) is highly desired. Indeed, the new class of optical PMCs such as Sb₂S₃, Sb₂Se₃ and Ge₂Sb₂Te₃Se₂ were reported to be suitable for a low-loss optical switch and a plasmonic devices because these materials have wider band gap [1-3], namely smaller extinction coefficient than GST.<br/>Here, we report on the simulation-based characterization and design of optical PCMs. We performed first principles calculations to find out new optical PCMs by using Vienna Ab initio Simulation Package (VASP). It was found that the partly substitutions of S atoms for Te atoms can enlarge the band depending on the composition and the position of the substitution sites. Based on the simulation results, a new composition Ge₂Sb₂Te₃S₂ (GSTS) was found to possess wider band gap than GST and expected to be used for a low-loss optical switch. We carried out the experimental evaluation of the optical properties of the thin film of GSTS by spectroscopic ellipsometry. We also report on the performance of the GSTS optical switches and propose a low-insertion-loss and non-volatile optical switches working near-infrared and mid-infrared wavelength ranges [4-5]. Part of this presentation is on the result obtained from the commissioned research (JPJ012368C03701) by National Institute of Information and Communications Technology (NICT), JAPAN and JSPS KAKENHI Grant Number JP24K00949.<br/><br/>[1] M. Delaney <i>et al.</i>, Adv. Func. Mater. 30, 2002447 (2020).<br/>[2] Y. Zhang <i>et al.</i>, Nat. Commun. 10, 4279, (2019)<br/>[3] L. Lu <i>et al.</i>, ACS Nano 15, 19722, (2021).<br/>[4] Y. Miyatake <i>et al.</i>, IEEE Trans. Electron Devices, 70, 2106, (2023).<br/>[5] Y. Miyatake <i>et al.</i>, J. Light. Technol., DOI: 10.1109/JLT.2024.3408877, (2024).