Thickness-dependent optical and structural properties of chalcogenide phase-change memory thin films grown at room temperature by pulsed laser deposition

Abstract

Phase-change materials, such as GeTe and Sb2Te3 alloys, are of great interest for applications in photonics, data storage, and computing due to their ability to rapidly and reversibly switch optical properties during phase transitions. This study investigates the thickness-dependent optical and structural properties of GeTe and Sb2Te3 thin films, deposited on amorphous substrates at room temperature using pulsed laser deposition. GeTe films, measured over a thickness range of 1.8–72.4 nm, show notable changes below 20 nm, with the high-frequency dielectric constant (εinf) increasing from 8.9 to 14.0 and the optical bandgap (Eg) decreasing from 0.95 to 0.74 eV. These variations are primarily attributed to quantum confinement effects in the amorphous GeTe structure. Sb2Te3 thin films develop with thickness, from mostly amorphous at 3.4 nm to partially amorphous-crystalline at 5.1–10 nm and finally to fully polycrystalline at larger thicknesses. Thinner films exhibit up to a 1.5% reduction in the c-lattice parameter, while thicker films show a clear change in crystal orientation. Correspondingly, εinf rises from 14.1 to 41.0, and Eg decreases from 0.69 to 0.41 eV. These results demonstrate how film thickness strongly influences the microstructure and optical behavior of PCMs, providing valuable insights for tailoring their properties in future electronic and optoelectronic applications.