2020, Kraft, Nikolas, Wang, Guoxiang, Bryja, Hagen, Prager, Andrea, Griebel, Jan, Lotnyk, Andriy

Ge-Sb-Te alloys are promising materials for non-volatile memory applications. Alloying of the materials with various elements is considered as prospective approach to enhance material properties. This work reports on the preparation and characterization of pure Ge-Sb-Te-O (GSTO) and alloyed with La-Sr-Mn-O (LSMO) thin films. Thermal heating of amorphous thin films to different temperatures show distinct crystallization behavior. A general trend is the decrease in the size of GSTO crystallites and the suppression in the formation of stable trigonal GSTO phase with increasing content of LSMO. Microstructural studies by transmission electron microscopy show the formation of metastable GSTO nanocrystallites dispersed in the amorphous matrix. Analysis of local chemical bonding by X-ray spectroscopy reveal the presence of different oxides in the GSTO-LSMO composites. Moreover, the composites with a high LSMO content exhibit higher crystallization temperature and significant larger sheet resistance in amorphous and crystalline phase, while a memory device made of GSTO-LSMO alloy reveals bipolar switching and synaptic behavior. In addition, the amount of LSMO in GSTO-LSMO thin films influences their optical properties and band gap. Overall, the results of this work reveal the highly promising potential of GSTO-LSMO nanocomposites for data storage and reconfigurable photonic applications as well as neuro-inspired computing.

2020, Wang, Guoxiang, Shi, Haizhou, Lotnyk, Andriy, Shi, Daotian, Wang, Rongping

Phase-change films with multiple resistance levels are promising for increasing the storage density in phase-change memory technology. Diffusion-dominated Zn2Sb3 films undergo transitions across three states, from high through intermediate to low resistance, upon annealing. The properties of the Zn2Sb3 material can be further optimized by doping with Bi. Based on scanning transmission electron microscopy combined with electrical transport measurements, at a particular Bi concentration, the conduction of Zn-Sb-Bi compounds changes from p- to n-type, originating from spinodal decomposition. Simultaneously, the change in the temperature coefficient of resistivity shows a metal-to-insulator transition. Further analysis of microstructure characteristics reveals that the distribution of the Bi-Sb phase may be the origin of the driving force for the p–n conduction and metal-to-insulator transitions and therefore may provide us with another way to improve multilevel data storage. Moreover, the Bi doping promotes the thermoelectric properties of the studied alloys, leading to higher values of the power factor compared to known reported structures. The present study sheds valuable light on the spinodal decomposition process caused by Bi doping, which can also occur in a wide variety of chalcogenide-based phase-change materials. In addition, the study provides a new strategy for realizing novel p–n heterostructures for multilevel data storage and thermoelectric applications.