| In-Situ XAFS Study of Amorphous Ge50Se50 Film under DC Electric Field |
| Sang Yeol SHIN |
| Korea Aerospace University |
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Ovonic threshold switching (OTS) of amorphous chalcogenide film is normally more reproducible and durable than that of other amorphous materials. For practical switching devices application, a good amorphous chalcogenide film showing OTS phenomenon should maintain its non-crystalline state during operation without temperature- or current- induced crystallization. In this respect, OTS of amorphous film in binary Ge-Se system is quite attractive thanks to its reasonably high electrical conductivity as well as wide operation temperature range given by crystallization temperature exceeding 300 oC. Indeed, quite a good performance of OTS device was recently achieved using equiatomic Ge50Se50 film [1, 2]. The underlying mechanism of OTS, however, has not been fully resolved despite a number of previous investigations. As such, in an effort to better understand OTS of amorphous chalcogenide film, in this study, we employ in-situ X-ray absorption spectroscopic analysis of Ge50Se50 film under DC electric field being applied.
Preliminary EXAFS study of this equiatomic GeSe film with no applied electric field reveals that the local atomic environments of each constituent atom undergo conspicuous changes during the phase change. Specifically, its amorphous structure satisfies the 4(Ge):2(Se) arrangements, which becomes the 3(Ge):3(Se) arrangements after crystallization [3]. This clear structural contrast associated with crystallization would facilitate our in-situ XAFS analysis. Based on this consideration, we have designed a suitable geometry of specimen for obtaining X-ray absorption spectra during electric field being applied. XANES and EXAFS spectra of both Ge K- and Se K-edges are delineated in relation to magnitude of applied DC electric field. Information thus obtained is explained in connection with the non-ohmic I-V characteristics of this equiatomic GeSe film.
References:
[1] S.-D. Kim, H.-W. Ahn, S.Y. Shin, D.S. Jeong, S.H. Son, H. Lee, B.-k. Cheong, D.W. Shin and S. Lee, Electrochem. Solid-State Lett. 2 (2013) Q75.
[2] D.S. Jeong, H. Lim, G.H. Park, C.S. Hwang, S. Lee and B.-k. Cheong, J. Appl. Phys. 111 (2012) 102807.
[3] S.Y. Shin, R. Golovchak, S. Lee, B.-k. Cheong, H. Jain and Y.G. Choi, Scripta Mater. 86 (2014) 56.
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| Acknowledgements : This work has been supported by NSF¡¯s International Materials Institute for New Functionality in Glass (IMI-NFG) through Grant No. DMR 0844014, and also by Basic Science Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2003832). |
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