GE K-EDGE EXTENDED X-RAY ABSORPTION FINE-STRUCTURE STUDY OF THE LOCAL-STRUCTURE OF AMORPHOUS GETE AND THE CRYSTALLIZATION

The local structure and crystallization of amorphous GeTe (a-GeTe) were examined by means of Ge K-edge EXAFS. In a-GeTe, both Be-Be and Be-Te bonds were observed to exist in nearest neighbors of Ge. The average coordination number around Ge is 3.7, which is close to the tetrahedral structure. A random covalent network (rcn) model seems to be suitable for the local Structure. After a-GeTe crystallized at 129-degrees-C, the Ge-Ge bond disappears and the Ge-Te bond length increases considerable. As temperature rises, in a-Ge-Te the Debye-Waller factor of the GE-Te bond increases greatly, while that of the Ge-Ge bond increases only slightly. At the crystallization, it is found that the fluctuation of the Ge-Te bond length plays a major role in the change of the local structure and bonding state around Ge.