Ferroelectricity in untwisted heterobilayers of transition metal dichalcogenides

Two-dimensional materials with out-of-plane (OOP) ferroelectric and piezoelectric properties are highly desirable for the realization of ultrathin ferro- and piezoelectronic devices. We demonstrate unexpected OOP ferroelectricity and piezoelectricity in untwisted, commensurate, and epitaxial MoS2/WS2 heterobilayers synthesized by scalable one-step chemical vapor deposition. We show d(33) piezoelectric constants of 1.95 to 2.09 picometers per volt that are larger than the natural OOP piezoelectric constant of monolayer In2Se3 by a factor of similar to 6. We demonstrate the modulation of tunneling current by about three orders of magnitude in ferroelectric tunnel junction devices by changing the polarization state of MoS2/WS2 heterobilayers. Our results are consistent with density functional theory, which shows that both symmetry breaking and interlayer sliding give rise to the unexpected properties without the need for invoking twist angles or moire domains.

Automated summary

We have successfully demonstrated unexpected out-of-plane ferroelectric and piezoelectric properties in MoS2/WS2 heterobilayers, which can be utilized in ultrathin ferro- and piezoelectronic devices.