Phase Change in (GeTe)1-x(Sb2Te3)x Investigated by Hard X-ray Photoemission Spectroscopy
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1072-G02-07
Phase Change in (GeTe)1-x(Sb2Te3)x Investigated by Hard X-ray Photoemission Spectroscopy Keisuke Kobayashi1, Jung-Jin Kim2,3, Toshiyuki Matsunaga4, Kouichi Kifune5, Eiji Ikenaga2, Masaaki Kobata1, Shigonori Ueda1, Rie Kojima6, and Noboru Yamada6 1 National Institute for Materials Science, Spring 8, 1-1-1 Kouto, Sayo-Cho, Hyogo, 679-5148, Japan 2 Japan Synchrotron Radiation Research Institute, Spring 8, 1-1-1 Kouto, Sayo-Cho, Hyogo, 6795198, Japan 3 present affiliation, Samsung Electronics Ltd. Ltd., San#16 Banwol-Dong,Gyeonggi-Do, Hwasung-city, 445-701, Korea, Republic of 4 Characterization Technology Group, Materials Science and Analysis Technology Center, Matsushita Electric Industry Co. Ltd., 3-1-1 Yagumo- Nakamachi, Moriguchi, Osaka, 570-8501, Japan 5 Faculty of Liberal Arts and Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka, 599-8531, Japan 6 AV Core Technology Development Center, Matsushita Electric Industrial Co., Ltd., 3-1-1 Yagumo- Nakamachi, Moriguchi, Moriguchi, Osaka, 570-8501, Japan ABSTRACT The crystalline phase of (GeTe)1-x(Sb2Te3)x (GST) has been identified as having a NaCl-type cubic structure with random occupation of the A sites by Ge, Sb and vacancies, and 100% occupation of B sites by Te. This fact calls our attention to a possible close relation of the pcrystalline-amorphous phase change to the inherent crystal bonding instability observed for the average five valence electrons () family. We present here the results of systematic hard X-ray photoemission experiments on GST films with various compositions, and discuss that a similar chemical bonding instability does indeed play an essential role in the phase change mechanism in GST. We propose a model for the fast phase change, in which 6 fold to 3 fold transition of p-like bonding play an essential role, in this class of materials. INTRODUCTION The (GeTe)-(Sb2Te3) pseudo binary alloy system (GST) has been intensively studied for the research and development of optical and electronic rewritable memory devices. The amorphouscrystalline phase transition in this alloy system attracts much attention both in applied and basic research fields, however, no generally accepted understandings on the mechanism has yet been established. Recently important reports on the amorphous structure of GSTs were published by different groups basing upon experiments. Kobolov et al. [1] have conducted XAFS experiments, and proposed the umbrella-flip model. Local reconstruction of the 6-fold bonds Fig. 1 HX-PES experimental configuration to the sp3-like 4-fold bonds is the key to the at BL47XU in SPring-8
phase change in this model. Basing upon the reverse reverse Monte Carlo (RMC) analysis of diffraction results, Kohara et al. [2] have recently reported that amorphous phase is dominated by nearly rectangular 3-fold bonds. We have also irradiated the problem from the different direction by the high brilliant undulator X-rays of SPring-8 [3], using high resolution hard X-ray photoemission spectroscopy with much larger probing depths (H
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