Large Optical Transitions in Rewritable Digital Versatile Discs: An Interlayer Atomic Zipper in a SbTe Alloy
- PDF / 834,060 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 71 Downloads / 189 Views
1072-G06-02
Large Optical Transitions in Rewritable Digital Versatile Discs: An Interlayer Atomic Zipper in a SbTe Alloy Junji Tominaga, Paul Fons, Takayuki Shima, Masashi Kuwahara, Osamu Suzuki, and Alexander Kolobov Center for Applied Near-Field Optics Research, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, 305-8562, Japan ABSTRACT Chalcogenides, in particular germanium-antimony-tellurium (GeSbTe) and antimony-rich tellurium (RSbTe) based alloys, are the most technologically significant alloys currently being applied to recordable optical storage as typified by rewritable digital versatile discs (DVD-RW), DVD random access memory, (DVD-RAM). The same alloys are also being applied to nonvolatile random access memory electrical memory in the form of phase change random access memory (PCRAM). In 2004, the phase transition mechanism of GeSbTe was first revealed, demonstrating that the amorphous state is not a random configurational network but is locally well-ordered with the crystalline to amorphous switching process being based upon Ge atoms moving between octahedral and tetrahedral symmetry positions. The kinetic barrier between these two states gives rise to the non-volatile nature of GeSbTe as a storage medium. In contrast, no theoretical analysis has been proposed for SbTe alloys because a Ge-free system. In this paper, the Sb2Te structure has been investigated using the local density approximation (LDA) using a plane-wave basis and compared with experimental results. The effect of external stress on the structure was also investigated. It was found that Sb2Te undergoes two phase-transitions at around 18 GPa (compressive) and –3 GPa (tensile). In the case of negative stress, the c-axis was found to expanded more than the other axes, giving rise a large refractive index change. We report on coherent (uniaxial) melting induced by the breaking a sigma bond between Sb2Te3 and Sb superlattices. We believe this to be the origin of the phase transition that induces a large change in physical properties.
INTRODUCTION Antimony (Sb)-rich tellurite (R-SbTe) both in pure form and with the addition of additional alloying components have been used as recording materials in re-writable digital versatile discs (DVD-RW) in the same was as germanium-antimony-tellurium alloys (GeSbTe) have been used in DVD-random access memory (DVD-RAM) [1, 2]. On the other hand, these same materials are also attractive for utilization in phase change random access memory (PCRAM)[3]. It is well known that these two alloys are typical chalcogenides and give rise to large changes in refractive index (Δn>1) and electronic conductivity (Δσ>103) between amorphous and crystalline phases [Ref. 4-5]. However, the mechanism behind the large change in refractive index of GeSbTe was not understood until 2004 as the amorphous state had long been assumed to be at random configurational network [4]. Kolobov et al. first pointed out that the so-called amorphous phase of GeSbTe was not in fact a ran
Data Loading...
