Designing a Low-Loss Phase Change Material Platform for High-Performance Tunable Photonic Multi-Level Devices

Tunable photonic multi-level devices (TPMDs), with their low power consumption, multi-state programmability, and massive parallelism, are critical building blocks for next-generation photonic computing. However, the performance of TPMDs is fundamentally limited by a trade-off in conventional phase-change materials (PCMs): the inability to simultaneously achieve a low extinction coefficient (k) for low insertion loss (IL) and a high refractive index contrast (Δn) for a large extinction ratio (ER). Here, using a Se saturated substitution strategy, we successfully engineered GeSe0.3Te0.7to simultaneously possess a wide bandgap and an metavalant bonding. The resulting material exhibits an outstanding FoM of 27.2, a value 20-fold, 5-fold, and 6-fold greater than those of Ge2Sb2Te5, GeTe and Ge2Sb2Se4Te1, respectively. Femtosecond laser experiments demonstrate the material's reliable reversible switching performance and its capacity for high-precision, arbitrary pattern writing. The TPMD constructed from GeSe0.3Te0.7achieves a synergistic optimization of a high ER, low IL, and high Q. This work not only provides a promising new material for high-performance photonic applications but also introduces a generalizable strategy—saturated solid-solution substitution—for designing novel PCMs that combine a high Δn with a low k.