Effect of sputter deposition parameters on the optical contrast and phase-change dynamics of Ge2Sb2Te5 thin films for reconfigurable photonic devices

ABSTRACT The chalcogenide phase-change material Ge2Sb2Te5 (GST) is paramount for developing next-generation reconfigurable photonic devices, yet its performance is critically dependent on thin-film quality. This work presents a systematic investigation into the influence of radio-frequency (RF) magnetron sputtering parameters—specifically argon (Ar) working pressure and substrate temperature—on the structural, chemical, optical, and kinetic properties of GST thin films. Films were deposited on SiO2/Si substrates under varying Ar pressures (0.4–3.0 Pa) and substrate temperatures (Room Temperature–160 °C). Comprehensive material characterization was performed using a suite of advanced analytical techniques. Results indicate that increasing Ar pressure leads to the formation of films with lower density and higher porosity, as confirmed by scanning electron microscopy analysis. This porous microstructure facilitates a lower crystallization temperature and faster crystallization dynamics, with switching times on the order of tens of picoseconds observed via time-resolved pump-probe reflectivity. However, this enhancement in switching speed is accompanied by a significant reduction in the optical contrast, a key figure of merit for photonic applications. Conversely, elevating the substrate temperature to an optimal 80 °C during deposition produces dense, pore-free amorphous films with a density of 6.16 g/cm3, only 1.5% lower than the crystalline phase. These films exhibit superior thermal stability and a maximized refractive index contrast (Δn) at telecommunication wavelengths. X-ray photoelectron spectroscopy confirmed that a protective capping layer is essential to prevent the rapid surface oxidation of Ge. These findings establish a clear process-structure-property-performance relationship, providing a crucial framework for tuning GST film properties to meet the divergent demands of high-speed, low-power optical memories versus high-performance, low-loss tunable photonic components.