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Chalcogenide materials play essential roles in modern nonvolatile memory technology in the form of both phase‐change memory (PCM) and selector devices. Herein, Bi–Te binary alloys are explored as an alternative candidate for superlattice (SL) or interfacial PCM (iPCM). GeTe/Bi4Te3 (GT/BT) SL exhibits similar structural features to conventional GeTe/Sb2Te3 (GT/ST) SL, such as highly oriented crystal grains and intermixing. Furthermore, preliminary device measurements show that Ge–Bi–Te (GBT) SL switches in a similar manner to conventional Ge–Sb–Te (GST), suggesting that they may be a promising candidate for memory applications. In addition, Bi2Te3/Sb2Te3 (BT/ST) heterostructure films have been successfully fabricated and show clear interface stacking at the atomic level. Although the BT/ST heterostructure is ostensibly a p–n junction, rectifying behavior is not observed in current (I)–voltage (V) measurements due to the existence of a large number of carriers in both layers. Finally, density functional theory (DFT)‐based simulations suggest that an ideal BT/ST heterostructure may possess intriguing topological properties that can enable novel functional devices. The Bi–Te binary alloys offer promising potential for optimizing PCM performance as well as for the realization of novel functional electronic devices. [ABSTRACT FROM AUTHOR]

This paper summarizes recent progress on thin film growth of chalcogenides by sputtering. The materials discussed include Sb–Te, Bi–Te, Ge–Te, and their superlattices, materials that are technologically important particularly for non-volatile phase change memory. In this work, the sputter-growth behavior of high-quality layered chalcogenide films is discussed. Sputtering is one of the most commonly used thin-film growth techniques in the semiconductor industry, however, the complex interrelationship between growth parameters can lead to difficulty in fabricating high-quality films although the deposition method itself is relatively simple. Here, we successfully demonstrate the fabrication of highly-oriented layered chalcogenide materials by sputtering. The selection of the appropriate sputtering target is important. In particular, it was found that a Te-rich Sb–Te alloy target such as Sb33Te67 is necessary in order to obtain a stoichiometric Sb2Te3 film. Moreover, the growth temperature is also a key factor in obtaining a highly-oriented film, namely the ideal growth temperature for an Sb2Te3 film is between 230 °C and 250 °C after the growth of an amorphous seed layer at room temperature. Furthermore, it was found that this technique is also useful to grow films epitaxially on Al2O3 or Si(111) substrates even though there are some misoriented grains as well as twins present. Finally, we demonstrate the growth of highly-oriented Sb2Te3 films on a flexible substrate. The versatility of sputtering will become technologically more and more important for the various applications represented by phase change memory. [ABSTRACT FROM AUTHOR]

2D van der Waals chalcogenides such as topological insulators and transition-metal dichalcogenides and their heterostructures are now at the forefront of semiconductor research. In this paper, we discuss the fundamental features and advantages of van der Waals bonded superlattices over conventional superlattices made of 3D materials and describe in more detail one practical example, namely, interfacial phase change memory based on GeTe–Sb2Te3 superlattice structures. [ABSTRACT FROM AUTHOR]

Phase-change memories based on reversible amorphous-crystal transformations in pseudobinary GeTe-Sb2Te3 alloys are one of the most promising nonvolatile memory technologies. The recently proposed superlattice-based memory, or interfacial phase-change memory (iPCM), is characterized by significantly faster switching, lower energy consumption, and better endurance. The switching mechanism in iPCM, where both the SET and RESET states are crystalline, is still contentious. Here, using the ab initio density functional theory simulations, a conceptually new switching mechanism for iPCM is derived, which is based on the change in the potential landscape of the bandgap, associated with local deviations from the pseudobinary stoichiometry across the van der Waals gaps and the associated shift of the Fermi level. The crucial role in this process belongs to Ge/Sb intermixing on the cation planes of iPCM. These findings offer a comprehensive understanding of the switching mechanisms in iPCM and are an essential step forward to the insightful development of phase-change memory technology. [ABSTRACT FROM AUTHOR]

Ge–Sb–Te alloy based phase‐change memory devices have recently been shown to be switchable in a bipolar mode. However, to date bipolar switching has only been demonstrated at relatively low speeds (on the order of tens of µs), and with endurance limited to 104 switching cycles. In this work, in lieu of a Ge–Sb–Te alloy, fast and durable bipolar switching is demonstrated in interfacial phase change memory (iPCM). It is revealed that in iPCM devices, bipolar switching can be carried out at least a factor of 1000 times faster and with at least 1000 times greater endurance than in conventional Ge–Sb–Te alloy based phase‐change devices. Additionally, bipolar switching was found to exhibit a larger RESET to SET resistance ratio and lower power consumption compared to conventional Ge–Sb–Te alloy based devices. [ABSTRACT FROM AUTHOR]

Coherent phonons (CPs) generated by laser pulses on the femtosecond scale have been proposed as a means to achieve ultrafast, nonthermal switching in phase-change materials such as Ge2Sb2Te5 (GST). Here we use ultrafast optical pump pulses to induce coherent acoustic phonons and stroboscopically measure the corresponding lattice distortions in GST using 100-ps x-ray pulses from the European Synchrotron Radiation Facility (ESRF) storage ring. A linear-chain model provides a good description of the observed changes in the diffraction signal; however, the magnitudes of the measured shifts are too large to be explained by thermal effects alone, implying the presence of excited-state effects in addition to temperature-driven expansion. The information on the movement of atoms during the excitation process can lead to greater insight into the possibilities of using CP-induced phase transitions in GST. [ABSTRACT FROM AUTHOR]

This work reveals that doping Ag into Sb 2 S 3 substantially decreases its crystallisation temperature. We show that applying an electric field to Sb 2 S 3 through Ag electrodes provides control of the crystallisation temperature and crystallisation rate. The crystal nuclei incubation time decreases substantially when the applied electric field is set to 200 kV/m. The applied electric field appears to force the Ag cations through the amorphous chalcogenide film resulting in Ag doped Sb 2 S 3 filaments that extend from the cathode to the anode. This was confirmed by X-ray fluorescence composition mapping. Density functional theory molecular dynamics modelling of Ag doped Sb 2 S 3 reveals that the diffusion constant of Ag is twice that of Sb or S over a wide temperature range, which implies that the Ag atoms are mobile in the amorphous Sb 2 S 3 structure. The applied electric field provides a mechanism to enhance the crystallisation kinetics of Ag-doped Sb 2 S 3 . [ABSTRACT FROM AUTHOR]