Incorporating Si into Sb ₂ Se ₃ : Tailoring Optical Phase Change Materials via Nanocomposites

ABSTRACT Optical phase change materials (OPCMs) have attracted attention for their versatility as nonvolatile photonic modulators. Discovering novel materials or engineering existing ones is therefore crucial to achieving the performance that current materials lack. Here, we employ co‐sputtering to investigate the doping of Si into Sb 2 Se 3 . We investigate the optical, structural, and thermal properties and compare results with those obtained from first‐principles calculations. We also study the crystallization and melt‐quenching via nano‐differential scanning calorimetry (NanoDSC). We find that 20% Si increases the transparency window in both states, specifically to 800 nm in the amorphous phase, while reducing power consumption by lowering the melting temperature—at the cost of reducing the refractive index contrast and slowing the kinetics of the phase transition. Moreover, we demonstrate switching between the amorphous and crystalline states of Si‐Sb 2 Se 3 using electro‐thermal switching in photonic integrated devices, ∼100‐µm 2 microheaters, and the NanoDSC sensor. Importantly, we observe that phase segregation in recrystallized films forms a nanocomposite with Sb 2 Se 3 grains in an amorphous matrix, allowing both reversible switching and effective‐medium optical properties. By harnessing phase segregation rather than avoiding it, nanocomposites transform a potential failure mechanism into a design strategy, enabling deliberate tuning of OPCM properties through targeted dopant selection.