Influence of the composition on the thermoelectric and electro-physical properties of Ge-Sb-Te thin films for phase change memory application

Influence of the composition variation along the quasi-binary line GeTe-Sb2Te3 on the thermoelectric and electro-physical properties of thin films was investigated. GST amorphous thin films have high Seebeck coefficients, which drops nearly on the order of magnitude after the crystallization. Temperature dependences of the resistivities were studied, and it was determined that crystallization temperature increases with moving along the quasi-binary line GeTe-Sb2Te3 from GeSb4Te7 to GeSb2Te4, and then to Ge2Sb2Te5, while the phase transition temperature range decreases. Current-voltage characteristics of amorphous thin films have three voltage ranges with different dependencies due to the different mechanisms of charge carrier transport

NEW DYES BASED ON THIENO[3,2-b]INDOLE WITH AN EXTENDED Π-CONJUGATION SYSTEM FOR DYE-SENSITIZED SOLAR CELLS

This work was supported by the Russian Foundation for Basic Research, project # 22-73-00291

Novel push-pull thieno[2,3-b]indole-based dyes for efficient dye-sensitized solar cells (DSSCs)

New metal-free sensitizers (IK 3-6), based on the thieno[2,3-b]indole ring system, bearing various aliphatic substituents at the nitrogen atom (electron-donating part), several thiophene units (π-bridge linker) and 2-cyanoacrylic acid (the electron-accepting and anchoring group) have been synthesized for application in dye-sensitized solar cells (DSSCs). The relationship between the IK dye structure and efficiency of the corresponding DSSC has been elucidated. Power conversion efficiency (PCE) up to 6.3% (short-circuit photocurrent density (JSC) 19.0 mA cm-2, open-circuit voltage (VOC) 0.59 V, and fill factor (FF) 56.4%) were obtained for the DSSC, based on 2-cyano-3-{5-[8-(2-ethylhexyl)-8H-thieno[2,3- b]indol-2-yl]thiophen-2-yl}acrylic acid (IK 3), which proved to be a highly synthetic available compound, under simulated AM 1.5 G irradiation (100 mW cm-2), thus indicating that thieno[2,3-b]indole-based organic dyes are perspective candidates for DSSCs. © 2017 Arkat. All rights reserved

Inter-diffusion of Plasmonic Metals and Phase Change Materials

This work investigates the problematic diffusion of metal atoms into phase change chalcogenides, which can destroy resonances in photonic devices. Interfaces between Ge2Sb2Te5 and metal layers were studied using X-ray reflectivity (XRR) and reflectometry of metal-Ge2Sb2Te5 layered stacks. The diffusion of metal atoms influences the crystallisation temperature and optical properties of phase change materials. When Au, Ag, Al, W structures are directly deposited on Ge2Sb2Te5 inter-diffusion occurs. Indeed, Au forms AuTe2 layers at the interface. Diffusion barrier layers, such as Si3N4 or stable diffusionless plasmonic materials, such as TiN, can prevent the interfacial damage. This work shows that the interfacial diffusion must be considered when designing phase change material tuned photonic devices, and that TiN is the most suitable plasmonic material to interface directly with Ge2Sb2Te5.Comment: 23 pages, 8 figures, articl

Investigation of the Crystallization Kinetics in Ge-Sb-Te-Bi Thin Films for Phase Change Memory Application

In this work the mechanism and kinetics of crystallization of the Ge₂Sb₂Te₅+Bi thin films were investigated using differential scanning calorimetry. Ge₂Sb₂Te₅ with different amounts of Bi (0, 0.2, 0.5, 0.8, 1, 3, 5 wt.%) was synthesized using quenching technique. Thin films were prepared by thermal evaporation of synthesized materials. X-ray diffraction has shown that synthesized materials had trigonal modification of Ge₂Sb₂Te₅. Introduction of Bi led to the appearance of trigonal modification of Bi₂Ge₂Te₅, which indicates on the replacement of Sb by Bi. As-deposited thin films were amorphous up to 3% of Bi. Higher concentrations of Bi led to the appearance of crystalline phases. Composition of thin films was verified by Rutherford backscattering, and was found to be close to that of the synthesized materials. The joint application of model-free Ozawa-Flynn-Wall and model-fitting Coates-Redfern methods allowed to estimate kinetic triplet for crystallization process of GST225+Bi thin films, and to predict data processing and storage times of the phase change memory cells. It was shown that GST225+0.5 wt.% Bi thin films have the most promising kinetic characteristics among the investigated materials, due to the predicted smallest data processing and largest storage times

Structure and electronic properties of amorphous As40Se30S30 films prepared by ion-plasma sputtering method

The atomic and local structure, as well as the electrical, optical, photoelectrical properties and drift mobility of charge carriers in amorphous As40Se30S30 films, prepared by the method of RF ion-plasma sputtering (RF-films), were studied in comparison with those of the films, prepared by the method of thermal vacuum evaporation (TE-films). These two methods differ significantly in the conditions of substance vaporization and condensation of atoms on a substrate. It was found that the films fabricated by the different methods have differences in structure and electronic parameters. The essential differences in photoconductivity and transport phenomena are observed, too. It was concluded that RF As40Se30S30 films have a modified structure. This leads to changes in the spectrum of extended and localized electronic states in these films, which, in its turn, causes differences in their electronic properties

THIN FILMS OF BINARY CHALKOGENIDES As2X3 (X = S, Se) PREPARED BY SPIN COATING METHOD

This paper describes the processes of preparing solutions of binary vitreous semiconductor materials As2X3 (X = S, Se) and fabricating thin films based on them by spin coating. The initial materials are synthesized using semiconductor purity grade solvents by the direct synthesis in pre-vacuumed quartz vials at a maximum temperature of 750ºС and identified by the authors as glass. The obtained amorphous thin films are proven to have an island morphology. The thickness of the As2S3 film can vary in the range of 200 nm (at an average roughness of 0.7 nm) to 2.5 μm (at an average roughness of 100 nm). The thickness of the As2Se3 film can vary in the range of 200 nm (at an average roughness of 8 nm) to 3 μm (at an average roughness of 200 nm). The optical characteristics of thin films are also studied, in particular optical transmission in the visible spectrum. The band gap of the obtained films is determined by employing a Tauc plot. The findings of the experiment are compared with the literature data