Elucidating temperature-dependent local structure change and optical properties in GeTe phase-change material

Phase-change memory emerges as a top contender for non-volatile data storage applications. We report here a systematic change in local structure and crystallization kinetics of binary GeTe thin films using temperature-dependent resistivity measurements, which offers single-stage crystallization at around 187 degrees C, corroborated with x-ray diffraction. Furthermore, the change in chemical bonding upon crystallization is determined through x-ray photoelectron spectroscopy core level spectra, which reveals the existence of Ge and Te components that align with the GeTe crystal structure. Also, an investigation was carried out employing a UV-Vis-NIR spectrophotometer to explore the evolution of optical bandgaps (E-g ), Tauc parameter ( B ) representing the local disorder, and Urbach energy (E-u) of the GeTe material, as it undergoes the transition from a disordered amorphous state to a crystalline state. As crystallization progresses, a consistent shift of E-g from 0.92 to 0.70 eV corresponds to as-deposited amorphous at room temperature and crystalline at 250 degrees C, respectively. In addition, the reduction in E- u (from 199.87 to 141.27 meV) and a sudden increase of B around crystallization temperature is observed upon increasing temperature, indicating direct observation of enhanced medium-range order and distortion in short-range order, respectively, in GeTe thin films, revealing improved structural and optical properties. These enhancements make the GeTe material ideal for data storage applications of phase-change memory for next-generation computing technology.