Ab initio investigation of ultrathin films of phase-change materials

Chalcogenide phase change materials such as GeTe and GeSbTe are capable of switching between the crystalline and the amorphous state on a nanosecond time scale at elevated temperatures. Furthermore, the two states exhibit a large electrical contrast, which is exploited in novel storage-class memory devices. The continuous miniaturization of such devices requires an understanding of the structural and electronic properties of these compounds in the quasi two-dimensional limit. Besides, few-layer crystalline films of GeTe and similar monochalcogenides have recently drawn attention because they display a peculiar in-plane ferroelectricity. In this work, we investigate thin layers of selected chalcogenides with varying thickness by first principles calculations based on density functional theory. We study the changes in said properties as a function of film thickness. We rationalize these changes in terms of bonding mechanisms and effects of depolarizing fields.