Correlation between crystallization behavior, electrical switching and local atomic structure of Ge–Te glasses Manisha Upadhyay, Sevi Murugavel ⁎ Department of Physics and Astrophysics, University of Delhi, Delhi – 110007, India abstract article info Article history: Received 22 December 2012 Received in revised form 20 February 2013 Available online 22 March 2013 Keywords: chalcogenide glass; crystallization kinetics; electrical switching We report the results of the crystallization behavior, electrical switching and structure of the bulk Ge x Te 100-x glasses to ascertain the role of composition on phase change behavior. Obtained quantities like crystallization temperature and switching parameters exhibit threshold behavior at x = 17 and 22. Within this compositional range, we find that measured properties are insensitive to x content and beyond this composition window it shows strong composition dependence and may be driven by the ordering among the structural units. The order- ing of the glass molecular structure becomes maximized and shows anomalous behavior at x = 20 (x c ). An effort has been made to understand the electrical switching characteristics and variation of threshold switching fields with Ge content on the basis of local atomic structure. The thickness dependence of switching fields and cyclability of these glasses identifies the mechanism of switching and influence of local atomic structure. The ob- served compositional variations are interpreted on the basis of the local atomic structure of the given glass and the corresponding crystalline phase. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. 1. Introduction Chalcogenide glasses are interesting class of materials which possess unique combination of properties including fast crystallization of the amorphous state accompanied by a drastic change in their electronic properties such as optical reflectivity and electrical resistance. Such large contrast in the optical and electrical properties of these materials makes us to use them as potential candidate for the optical and electrical data storage applications. Nearly four decades back Ovshinsky reported the first switching and memory effects in these classes of materials with complex systems like Si 12 Te 48 As 30 Ge 10 , Ge 15 Tl 81 Sb 2 S 2 , Ge 10 Te 5 In 2.5 Ga 2.5 etc. that draw much attention of various researchers [1–3]. Later, it has been found that the pseudobinary compounds of GeTe–Sb 2 Te 3 (GST) al- loys are the most suitable candidate for the commercial phase change memory (PCM) devices. In 1987, these GST alloys were introduced by SONY with 500 Mb in the rewritable optical disc, since then memory has increased to 50 Gb in blu-ray disc. The flash memory has been obeying Moore's law of scaling and it has achieved limiting value of 64 Gb NAND flash memory with 30 nm feature size. Hence, the size limiting feature can be overcome by the PCM based materials and it could be the next generation non-volatile memory for the successful replacement of currently used flash memory. More recently, it has been shown that nanostructured devices such as GeTe nanowires of as small as two to three times the lattice constant retain their phase change properties and it could remove the scaling limit of flash memory with phase change technology [4]. The increasing demand on such devices largely depends on the thermal parameters such as crystallization temperature (T c ), crys- tallization speed and melting temperature (T m ) of the given glass composition. Since, the phase change technology is mainly based on the reversible switching between the crystalline and amorphous state induced by an electric field, light or combination of both [5]. In this context, the binary Ge–Te alloys, which exhibit superior thermal properties (higher T c ) than ternary Ge–Sb–Te (GST) alloy composi- tions, appear attractive, if their crystallization speed becomes ade- quately fast [6]. Furthermore, a sufficient knowledge of the thermal crystallization kinetics is necessary for the development of suitable phase-change materials with optimized parameters. Within the Ge– Te alloys, the stoichiometric Ge 50 Te 50 has attracted considerable in- terest due to the rapid crystallization and relative stability at ambient conditions. Recently, it has been shown that the eutectic, GeTe 6 ap- pears to be potential selector device, which exhibits Ovonic threshold switching behavior with superior performance in the switching pa- rameters. In this context, significant progress has been made in binary Ge–Te glass system with various compositions and found that the T c and crystallization speed exhibit a strong compositional dependence [7,8]. However, the reason behind such strong dependence of crystal- lization kinetics on chemical composition remains to be established. It is interesting to note that an early work done by Barton et al. revealed that the minimum pulse width required for crystallization of Ge–Te films has been found to be least for stoichiometric Ge 50 Te 50 composi- tion and it increases while shifting away from this composition [7]. Journal of Non-Crystalline Solids 368 (2013) 34–39 ⁎ Corresponding author. Tel.: +91 1127667061. E-mail address: murug@physics.du.ac.in (S. Murugavel). 0022-3093/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnoncrysol.2013.02.028 Contents lists available at SciVerse ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol