Abstract
Phase‐change alloys are the functional materials at the heart of an emerging digital‐storage technology. The GeTe‐Sb2Te3 pseudo‐binary systems, in particular the composition Ge2Sb2Te5 (GST), are one of a handful of materials which meet the unique requirements of a stable amorphous phase, rapid amorphous‐to‐crystalline phase transition, and significant contrasts in optical and electrical properties between material states. The properties of GST can be optimized by doping with p‐block elements, of which Bi has interesting effects on the crystallization kinetics and electrical properties. A comprehensive simulational study of Bi‐doped GST is carried out, looking at trends in behavior and properties as a function of dopant concentration. The results reveal how Bi integrates into the host matrix, and provide insight into its enhancement of the crystallization speed. A straightforward explanation is proposed for the reversal of the charge‐carrier sign beyond a critical doping threshold. The effect of Bi on the optical properties of GST is also investigated. The microscopic insight from this study may assist in the future selection of dopants to optimize the phase‐change properties of GST, and also of other PCMs, and the general methods employed in this work should be applicable to the study of related materials, for example, doped chalcogenide glasses.
Highlights
Phase-change alloys are the functional materials at the heart of an emerging has been shown in various studies to offer high endurance,[2] sub-nanosecond digital-storage technology
The microscopic insight from this study may assist in the future selection of dopants to optimize the phase-change properties of GST, and of other Phase-change materials (PCMs), and the general methods employed in this work should be applicable the properties of GST are not optimal, and much research has been conducted into enhancing some of its properties by doping, for example, increasing the thermal stability of the amorphous mateto the study of related materials, for example, doped chalcogenide glasses
The heart of phase-change random-access memory (PCRAM), Bi has been shown to have a range of interesting effects, one of a handful of digital-storage technologies which are both on GST hosts,[11,12,13] and on other PCM systems.[14,15]
Summary
We found that the average pressure was reduced with increasing Bi content, suggesting that the equilibrium density of the doped systems would be lower than the undoped one These differences in pressure are small, and, based on previous work, are not expected to influence the behavior of the material (e.g., crystallization dynamics) to a large extent.[28]. To investigate the structure and physical properties in more detail, amorphous and crystalline configurations of each system, taken from the end of the quench and annealing periods of the simulation, respectively, were energy-relaxed, with the cell volume and shape being allowed to vary. Further structural characterization and property calculations were carried out on these optimized models
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