Amorphous Ge2 Sb2 Te5 (a-GST) films were deposited by ion beam sputtering deposition. Extended x-ray absorption fine structure (EXAFS) data confirmed the existence of the Ge-Ge homopolar bonds in the films. Raman spectra also indicated that the Ge tetrahedral coordination in the a-GST film disappeared after an annealing treatment above 220 °C. Resonantly excited Ge L2,3 x-ray emission spectra (which probe occupied Ge 3d4s -electronic states) show that the phase change from the amorphous to crystalline state is accompanied by a reduction in the Ge I (L2)/I (L 3) intensity ratio due to a L2 L3 N Coster-Kronig transition, indicating that the number of carriers is increased in the Ge 4sp valence state. These findings constitute direct evidence for the contribution of the Ge electronic states to the resistivity change.
Bibliographical noteFunding Information:
This research was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea, and a joint program between Yonsei University-Hynix Semiconductor Inc. We also acknowledge support from the National Sciences and Engineering Research Council of Canada (NSERC). E.Z. acknowledges support of the Russian Science Foundation for Basic Research (Project No. 08-02-00148) and the Research Council of the President of the Russian Federation (Grant No. NSH-3572.2010.2).
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)