Phase Separation in Ge-Rich GeSbTe at Different Length Scales: Melt-Quenched Bulk versus Annealed Thin Films

• Published in: Nanomaterials (Basel, Switzerland) Vol. 12; no. 10; p. 1717
• Main Authors: Yimam, Daniel Tadesse, Van Der Ree, A J T, Abou El Kheir, Omar, Momand, Jamo, Ahmadi, Majid, Palasantzas, George, Bernasconi, Marco, Kooi, Bart J
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 18.05.2022; MDPI
• Subjects: Alloys; Annealing; Chemical composition; Composition; Crystallization; Density functional theory; EDX elemental chemical mapping; Electron microscopy; Ge-rich GST; Germanium; GGST; Lasers; Memory devices; Morphology; phase change materials; Phase separation; pulsed laser deposition; Quenching; Scanning electron microscopy; Software; Soldering; Ternary alloys; Thin films; Transmission electron microscopy; United States > US; GGST; phase separation; embedded memory; pulsed laser deposition; density functional theory; Ge-rich GST; phase change materials; EDX elemental chemical mapping
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano12101717

Integration of the prototypical GeSbTe (GST) ternary alloys, especially on the GeTe-Sb Te tie-line, into non-volatile memory and nanophotonic devices is a relatively mature field of study. Nevertheless, the search for the next best active material with outstanding properties is still ongoing. This search is relatively crucial for embedded memory applications where the crystallization temperature of the active material has to be higher to surpass the soldering threshold. Increasing the Ge content in the GST alloys seems promising due to the associated higher crystallization temperatures. However, homogeneous Ge-rich GST in the as-deposited condition is thermodynamically unstable, and phase separation upon annealing is unavoidable. This phase separation reduces endurance and is detrimental in fully integrating the alloys into active memory devices. This work investigated the phase separation of Ge-rich GST alloys, specifically Ge Sb Te or GST523, into multiple (meta)stable phases at different length scales in melt-quenched bulk and annealed thin film. Electron microscopy-based techniques were used in our work for chemical mapping and elemental composition analysis to show the formation of multiple phases. Our results show the formation of alloys such as GST213 and GST324 in all length scales. Furthermore, the alloy compositions and the observed phase separation pathways agree to a large extent with theoretical results from density functional theory calculations.