Designing a Switchable High-Optical- Contrast Material Platform for Visible Reconfigurable Nanophotonics

The integration of phase change materials (PCMs) with planar multilayer structures, metasurfaces, waveguides, and photonic integrated circuits has triggered a technological revolution in nonvolatile tunable nanophotonic devices. The performance of devices is largely determined by PCMs, which is highly desired to have a high optical contrast and switchable capability. Here, we present a novel material platform based on Ge0.9 Sb0.1 Te suitable for nanophotonics applications across the entire visible spectral region. Ge0.9 Sb0.1 Te exhibits an optical contrast of up to 66%, significantly higher than that of the most widely reported Ge2Sb2Te5 (30%~35%) and GeTe (45%~50%). Through experiments and first-principles calculations, we reveal that this excellent performance originates from the unique solid-solution structure of crystalline Ge0.9 Sb0.1 Te, which combines high structural order with a narrow optical band gap. Using ultrafast laser induction technology, we demonstrate that the crystalline state of Ge0.9 Sb0.1 Te can be arbitrarily written and erased, achieving 16 distinct optical levels, which exceeds the 7 levels of Ge2Sb2Te5. In addition, we demonstrated grayscale lithography based on Ge0.9 Sb0.1 Te, proving that Ge0.9 Sb0.1 Te has a broad range of application potential as a visible reconfigurable nanophotonic platform.