Stacking Dependent Piezoelectric Response of Bilayer and Heterobilayer Group-IV Monochalcogenides under Applied External Strain

Abstract

Layered two-dimensional (2D) materials are promising materials for piezoelectric and optoelectronic devices due to the introduction of new and interesting properties not seen in the single layers alone. In particular, the group-IV monochalcogenides (MX, M = Ge/Sn and X= S/Se) are highly piezoelectric layered materials which have outstanding optical adsorption properties in the isolated monlayer form. It is possible that combinations of MX monolayers, in a bilayer or heterobilayer system, could exhibit properties that are different to their monolayer counterparts. Using density functional theory calculations, the stacking-dependent piezoelectric response of group-IV monochalcogenide bilayers and heterobilayers with and without applied strain was determined. Of the four materials, SnSe yields the largest e22 value in both the monolayer (0.86 C/m2) and bilayer (1.36 C/m2) form. Of the different heterobilayers examined, GeSe/SnSe has the largest e22 value (1.58 C/m2). With the application of strain, the piezoelectric response can be significantly enhanced, allowing bilayer SnSe to achieve a maximum response of 6.13 C/m2, which is a ~450% increase compared to its unstrained form, and is 450-730% higher than reported for other layered materials, such as ZnO and MoSTe. Indirect-to-direct band gap transitions can also be achieved using differing stacking arrangements, with the GeSe/SnSe heterobilayer being determined to have a type II band gap, demonstrating there are potential applications for the heterobilayers in optoelectronic devices. Overall, the group-IV monochalcogenide bilayers have the potential to achieve extraordinary piezoelectric responses under applied strain, making them ideal for nano-based piezoelectric and optoelectronic devices.

Supplementary files

Article information

Article type
Paper
Submitted
30 Sep 2024
Accepted
01 Feb 2025
First published
03 Feb 2025

Nanoscale, 2025, Accepted Manuscript

Stacking Dependent Piezoelectric Response of Bilayer and Heterobilayer Group-IV Monochalcogenides under Applied External Strain

K. Tran and M. J. Sapountzis Spencer, Nanoscale, 2025, Accepted Manuscript , DOI: 10.1039/D4NR04020A

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