The Ge2Sb2Te5 and GeTe compounds are of interest for applications in phase change memories. In the reset process of the memory the crystal is rapidly brought above the melting temperature Tm by Joule heating and then the liquid phase rapidly cools down leading to the formation of the amorphous phase. Since the liquid above Tm is metallic and the amorphous phase is semiconducting a semiconductor-to-metal transition occurs in the supercooled liquid. Based on density functional simulations, we estimated the metal-semiconductor transition temperature TM-SC by monitoring the opening of a band gap in the supercooled liquid phase. Due to previous evidence on the importance of the van der Waals (vdW) interaction in describing the liquid phase of these materials, we used both the revised Vydrov-van Voorhis functional which includes vdW nonlocal interactions and the Perdew-Burke-Ernzerhof functional without vdW corrections. The estimated TM-SC is about 100-150 K higher with the former than with the latter framework for both compounds. By including vdW interactions the estimated TM-SC is closer to Tm than to the glass transition temperature for both systems. The analysis of the structural properties as a function of temperature suggests a correlation between the metal-semiconductor transition and a Peierls distortion. However, the data support more a continuous structural transformation than the presence of a first order liquid-liquid phase change associated the metal-semiconductor transition.

Cobelli, M., Dragoni, D., Caravati, S., Bernasconi, M. (2021). Metal-semiconductor transition in the supercooled liquid phase of the Ge2Sb2Te5 and GeTe compounds. PHYSICAL REVIEW MATERIALS, 5(4) [10.1103/PhysRevMaterials.5.045004].

Metal-semiconductor transition in the supercooled liquid phase of the Ge2Sb2Te5 and GeTe compounds

Dragoni D.
;
Caravati S.;Bernasconi M.
2021

Abstract

The Ge2Sb2Te5 and GeTe compounds are of interest for applications in phase change memories. In the reset process of the memory the crystal is rapidly brought above the melting temperature Tm by Joule heating and then the liquid phase rapidly cools down leading to the formation of the amorphous phase. Since the liquid above Tm is metallic and the amorphous phase is semiconducting a semiconductor-to-metal transition occurs in the supercooled liquid. Based on density functional simulations, we estimated the metal-semiconductor transition temperature TM-SC by monitoring the opening of a band gap in the supercooled liquid phase. Due to previous evidence on the importance of the van der Waals (vdW) interaction in describing the liquid phase of these materials, we used both the revised Vydrov-van Voorhis functional which includes vdW nonlocal interactions and the Perdew-Burke-Ernzerhof functional without vdW corrections. The estimated TM-SC is about 100-150 K higher with the former than with the latter framework for both compounds. By including vdW interactions the estimated TM-SC is closer to Tm than to the glass transition temperature for both systems. The analysis of the structural properties as a function of temperature suggests a correlation between the metal-semiconductor transition and a Peierls distortion. However, the data support more a continuous structural transformation than the presence of a first order liquid-liquid phase change associated the metal-semiconductor transition.
Articolo in rivista - Articolo scientifico
denisty functional theory, metal-insulator transition, phase change materials;
English
20-apr-2021
2021
5
4
045004
reserved
Cobelli, M., Dragoni, D., Caravati, S., Bernasconi, M. (2021). Metal-semiconductor transition in the supercooled liquid phase of the Ge2Sb2Te5 and GeTe compounds. PHYSICAL REVIEW MATERIALS, 5(4) [10.1103/PhysRevMaterials.5.045004].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/316142
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