Vortex‐Oriented Ferroelectric Domains in SnTe/PbTe Monolayer Lateral Heterostructures

Kai Chang, John W. D. Villanova, Jing‐Rong Ji, Souvik Das, Felix Küster, Salvador Barraza‐Lopez, Paolo Sessi, Stuart S. P. Parkin
2021 Advanced Materials  
valleytronic, optical, thermal, magnetic, and ferroelectric performances in novel heterostructures and devices. Their weak interlayer coupling allows the relatively straightforward fabrication of vertical heterostructures by mechanical stacking of 2D materials. On the other hand, the creation of lateral heterostructures (LHSs), which are the elementary structures of the conducting channels in modern metal-oxide-semiconductor field-effect transistor based microelectronics, is much less explored
more » ... s it requires more complex growth and doping techniques. Encouraged by the potential outstanding performance and versatile tuning freedom that can emerge out of 2D LHSs, multiple experimental and theoretical studies have been carried out in this field. [1] 9] [10] [11] [12] All these TMDC LHSs display diode-like electric current rectification effects. Meanwhile, prototype devices including photodiodes and complementary metal-oxidesemiconductor transistor inverters with high performance were fabricated , [7, [10] [11] [12] Through either well-controlled gas flow switching techniques or lithography assisted anion substitution, TMDC LHS superlattices with atomically sharp interfaces were created [13] [14] [15] In addition, TMDC LHSs composed of only one material, but with varying thicknesses, [16, 17] or dielectric environments [18] across their interface, generated modifications of the electronic bandgap, rectification, and photovoltaic effects. Additional forms of 2D LHSs that combine materials with different spatial symmetries, such as graphene-TMDC LHSs [19] [20] [21] [22] hBN-TMDC LHSs, [19] graphene nanoribbon LHSs with varying doping [23] or widths, [24] metallic-semiconducting TMDC LHSs, [25] and group-IV monochalcogenide-dichalcogenide LHSs, [26] have been created through various enhanced CVD approaches, such as mechanical-exfoliation-assisted CVD, [19] seed-promoted CVD, [20] template-growth defined by plasma etching, [21] and thermally converting the chemical compositions. [26] terostructures formed from interfaces between materials with complementary properties often display unconventional physics. Of especial interest are heterostructures formed with ferroelectric materials. These are mostly formed by combining thin layers in vertical stacks. Here the first in situ molecular beam epitaxial growth and scanning tunneling microscopy characterization of atomically sharp lateral heterostructures between a ferroelectric SnTe monolayer and a paraelectric PbTe monolayer are reported. The bias voltage dependence of the apparent heights of SnTe and PbTe monolayers, which are closely related to the type-II band alignment of the heterostructure, is investigated. Remarkably, it is discovered that the ferroelectric domains in the SnTe surrounding a PbTe core form either clockwise or counterclockwise vortex-oriented quadrant configurations. In addition, when there is a finite angle between the polarization and the interface, the perpendicular component of the polarization always points from SnTe to PbTe. Supported by first-principles calculation, the mechanism of vortex formation and preferred polarization direction is identified in the interaction between the polarization, the space charge, and the strain effect at the horizontal heterointerface. The studies bring the application of 2D group-IV monochalcogenides on in-plane ferroelectric heterostructures a step closer.
doi:10.1002/adma.202102267 fatcat:7s2rlxecvbhsbdd4xqzjbst6h4