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Interfacial phase‐change materials (iPCM), which are alternatively stacked with GeTe and Sb2Te3 in the superlattice structure, have been highlighted as next‐generation PCM with improved overall phase‐change characteristics. However, several studies have reported that a melt‐quenching process, whereby the initial superlattice structure is not maintained within the reversible switching process, rather than the initially proposed melting‐free phase‐change mechanism, occurs during operation. Herein, GeSbTe superlattices are synthesized using molecular beam epitaxy, and the reversible phases of the superlattice obtained by irradiation with an optical pulsed laser (KrF; 280 nm, 25 ns) and re‐annealing or by applying different electrical pulses are investigated through careful structural analyses. The results revealed that Te atoms are aligned parallel to the interface regardless of the reversible phase, whereas cations and inherent vacancies are distributed differently during the phase‐change process. The stability of memory cells with cycling operations can be enhanced by enriching inherent vacancies, and the switching energy can be reduced by expanding the interspaces via doping engineering. [ABSTRACT FROM AUTHOR]

Topological insulators have recently received attention in optoelectronic devices because of their high mobility and broadband absorption resulting from their topological surface states. In particular, theoretical and experimental studies have emerged that can improve the spin generation efficiency in a topological insulator‐based p–n junction structure called a TPNJ, drawing attention in optospintronics. Recently, research on implementing the TPNJ structure is conducted; however, studies on the device characteristics of the TPNJ structure are still insufficient. In this study, the TPNJ structure is effectively implemented without intermixing by controlling the annealing temperature, and the photocharacteristics appearing in the TPNJ structure are investigated using a cross‐pattern that can compare the characteristics in a single device. Enhanced photo characteristics are observed for the TPNJ structure. An optical pump Terahertz probe and a physical property measurement system are used to confirm the cause of improved photoresponsivity. Consequently, the photocharacteristics are improved owing to the change in the absorption mechanism and surface transport channel caused by the Fermi level shift in the TPNJ structure. [ABSTRACT FROM AUTHOR]

High‐performing 2D electrical and optical devices can be realized by forming an ideal van der Waals (vdW) metal contact with weak interactions and stable interface states. However, the methods for applying metal contacts while avoiding damage from metal deposition present challenges in realizing a uniform, stable vdW interface. To overcome this problem, this study develops a method for forming vdW contacts using a sacrificial Se buffer layer. This study explores this method by investigating the difference in the Schottky barrier height between the vdW metal contact deposited using a buffer layer, a transferred metal contact, and a conventional directly deposited metal contact using rectification and photovoltaic characteristics of a Schottky diode structure with graphite. Evidently, the Se buffer layer method forms the most stable and ideal vdW contact while preventing Fermi‐level pinning. A tungsten diselenide Schottky diode fabricated using these vdW contacts with Au and graphite as the top and bottom electrodes, respectively, exhibits excellent operation with an ideality factor of ≈1, an on/off ratio of > 107, and coherent properties. Additionally, when using only the vdW Au contact, the electrical and optical properties of the device can be minutely modulated by changing the structure of the Schottky diode. [ABSTRACT FROM AUTHOR]

In this study, spin‐to‐charge conversion (SCC) of various topological materials with ferromagnet is investigated using spintronic terahertz (THz) emission spectroscopy. Compared with other topological materials, significantly large THz emission is observed for topologically nontrivial phases of Bi1‐xSbx (x > 0.2) that predominantly originates from the topological surface state. When Bi is superposed above a certain stoichiometry of Bi1‐xSbx, it plays a crucial role in generating a highly spin‐split state and enhancing the spin‐mixing conductance, resulting in colossal THz emission. This proves that improving the SCC efficiency through interface engineering is a useful strategy to design a powerful spintronic device. Collectively, this study proposes a methodology for systematically analyzing SCC efficiency or spin Hall angle using THz emission spectroscopy and offers an efficient structure for future spintronic devices. [ABSTRACT FROM AUTHOR]

Topological insulator has gapless surface state, which results from bulk band inversion due to strong spin–orbit coupling. This nontrivial topology robust to nonmagnetic disorders and defects is considered one of the biggest obstacles for modulations of the surface state. In this work, the suppression of surface properties in Bi2Se3 of various thicknesses grown on antiferromagnetic NiO, which has a strong exchange interaction is investigated. Under perpendicular magnetic fields, a drastic decrease in mobility µ and in the number of phase coherent channels α in 5 QL Bi2Se3 on NiO are observed. In addition, the THz transmission study shows that an increase in the surface penetration depth ξ can accelerate the hybridization of surface states, which is also verified using the optical pump THz probe. This rapid collapse of surface states indicates the unique role of antiferromagnetic materials in band overlap, suggesting that the topological surface nature can be modulated by forming an antiferromagnet‐topological insulator heterostructure. [ABSTRACT FROM AUTHOR]