Temperature-dependent high-resolution X-ray photoelectron spectroscopic study on Ge₁Sb₂Te₄

Oxygen-free and amorphous Ge₁Sb₂Te₄ thin film was obtained in an ultra-high vacuum and then annealed in situ to the stable-phase temperature. High-resolution X-ray photoelectron spectroscopy using synchrotron radiation was performed on the film at the different annealing temperatures of 100, 130, 150, 180, and 250 °C. The Te 4d, Sb 4d, and Ge 3d shallow core levels as well as the valence-band spectra were acquired. In the shallow core-level spectra, we observed distinguishable changes in the Sb 4d and Ge 3d levels as the film phase changed. As the temperature increased, a higher binding-energy (BE) component appeared at the Sb 4d level, the intensity of the component increased, and the spin-orbit split feature was enhanced at the Ge 3d level. In the valence-band spectra, a slight increase was observed at 0-1, ~ 3, ~ 9, and ~ 12 eV BE, and a decrease, at ~ 1.5 and ~ 4.5 eV BE. The energy resolution employed in this study was about 150 meV.