Solution-Based Processing of the Phase-Change Material KSb₅S₈

Abstract

A hydrazine-based process for solution-depositing phase-change materials (PCMs) is demonstrated, using KSb 5 S 8 (KSS) as an example. The process involves dissolving the elemental metals and chalcogen in hydrazine at room temperature and spin-coating the solution onto a substrate, followed by a short low-temperature (T e 250 °C) anneal. The spin-coated KSS films, which range in thickness from 10 to 90 nm, are examined using variable temperature X-ray diffraction, medium energy ion scattering (MEIS), Rutherford backscattering spectroscopy (RBS), and scanning electron microscopy (SEM). The spincoated KSS films exhibit a reversible amorphous-crystalline transition with a relatively high crystallization temperature (∼280 °C). Selected other chalcogenide-based PCMs are also expected to be suitable for thin-film deposition using this approach.

Solution Processing of Chalcogenide Semiconductors via Dimensional Reduction

“…Phase-change materials (PCMs) represent a further important application for metal chalcogenide films, as a result of emerging memory technologies, including commercially available rewritable optical media (e.g., CD-RW, DVD-RW, DVR) [5,6,45,78,79] and the development of nonvolatile phase-change memory (PRAM). [80,81] A PCM film must be switchable between two physical states (i.e., usually amorphous and crystalline), with the change in state being detectable using a physical measurement, such as optical absorption, reflectivity, or electrical resistivity.…”

“…Application of the hydrazine-based film deposition process to PCMs has been demonstrated using KSb 5 S 8 as an example. [45] Unlike many chalcogenide glasses, KSb 5 S 8 is a congruently melting stoichiometric compound, with a relatively high glass-to-crystallization temperature (287 8C) and large optical band gap (i.e., 1.82 eV for crystalline and 1.67 eV for glass forms). [82] The KSb 5 S 8 precursor solution was prepared by carefully dissolving elemental potassium, antimony and sulfur in hydrazine under an inert atmosphere.…”

“…[39] The simple approach described in this report generally employs additional chalcogen (S, Se, Te), typically in anhydrous hydrazine, to directly improve the solubility and film forming properties of selected metal chalcogenides, including SnSe 2-x S x , In 2 Se 3 , GeS 2 , GeSe 2 , Cu 2 S, Sb 2 Se 3 , Sb 2 Te 3 , CuInSe 2 , Cu(In,Ga)Se 2-x S x , and Ga 2 Se 3 . [40][41][42][43][44][45][46][47] Dissolution generally proceeds by formation of metal chalcogenide anions accompanied by hydrazinium cations. The additional chalcogen added to the hydrazine facilitates the disruption of the metal chalcogenide framework by breaking up M-X-M linkages, in analogy to the dimensional reduction examples described above.…”

“…a) X-ray diffraction (l ¼ 1.797 Å) from a spin-coated KSb 5 S 8 film, demonstrating good agreement with b) a simulated diffraction pattern for bulk KSb 5 S 8 (using 18 peak fwhm in the modeling). Reproduced with permission from[45]. Copyright 2006 American Chemical Society.…”

On the Complexity of Crystallization of Thioantimonates: In‐situ Energy Dispersive X‐ray Diffraction (EDXRD) Studies of the Solvothermal Formation of the Isostructural Thioantimonates [TM(tren)Sb4S7] (TM = Fe, Zn)

“…Main group chalcogenometalates are intensively studied due to promising properties like tuneable optical band‐gaps,1 photoconductivity,2 low dimensional magnetic properties,3,4 unusual thermal expansion of the lattice parameters,5 phase change behavior,6–8 non‐linear optical behavior 9 or ion exchange properties 10,11 photoconductive properties,12 but also due to the fascinating, beautiful and variable structural chemistry 13–22. In several reviews the structural chemistry and properties of chalcogenometalates were discussed 23–28…”