Structural Phase Transitions between Layered Indium Selenide for Integrated Photonic Memory

The primary mechanism of optical memoristive devices relies on phase transitions between amorphous and crystalline states. The slow or energy‐hungry amorphous–crystalline transitions in optical phase‐change materials are detrimental to the scalability and performance of devices. Leveraging an integrated photonic platform, nonvolatile and reversible switching between two layered structures of indium selenide (In2Se3) triggered by a single nanosecond pulse is demonstrated. The high‐resolution pair distribution function reveals the detailed atomistic transition pathways between the layered structures. With interlayer “shear glide” and isosymmetric phase transition, switching between the α‐ and β‐structural states contains low re‐configurational entropy, allowing reversible switching between layered structures. Broadband refractive index contrast, optical transparency, and volumetric effect in the crystalline–crystalline phase transition are experimentally characterized in molecular‐beam‐epitaxy‐grown thin films and compared to ab initio calculations. The nonlinear resonator transmission spectra measure of incremental linear loss rate of 3.3 GHz, introduced by a 1.5 µm‐long In2Se3‐covered layer, resulted from the combinations of material absorption and scattering. Transition between two topologically similar layered structures in In2Se3 breaks the speed and energy limitations of photonic memory, via reversible nonvolatile refractive index change induced by a single nanosecond pulse. In this work, the atomistic phase‐change pathway between the layered structures is unraveled with in situ high‐energy X‐ray diffraction and integrated photonic switching with a transferred epitaxial layer is demonstrated. Detailed analysis on the volumetric effect and by nonlinear spectroscopy are provided to harness the mode coupling and loss in the hybrid device.