Enhanced Conductivity in Artificial Charged Domain Walls of van der Waals Ferroelectric Heterostructures

The stacking order of two-dimensional (2D) materials based heterostructure leads to emerging interfacial properties not found in the parent materials, such as sliding ferroelectricity or the formation of new states. In case of 2D ferroelectrics, stacking oppositely polarized domains leads to artificial charged domain walls which allows lateral current flow. This geometry provides a unique opportunity to address the longstanding challenge of quantifying the intrinsic carrier density, type, and mobility of charged domain walls in ferroelectrics.
In this work, we stack opposite polar domains of α-In₂Se₃ and controllably generate atomically sharp lateral charged domain walls. We explore the influence of the atomic scale interfacial polar discontinuity on the microscale electrical transport characteristics by combining temperature-dependent electrical transport measurement, piezo-force microscopy, scanning transmission electron microscopy, and density functional theory (DFT).
We show that stacking two oppositely polarized α-In₂Se₃ flakes leads to lateral tail-tail (T-T) or head-head (H-H) charged domain wall formation. At room temperature, the T-T and H-H domain walls show metal-like conductance which are more than 3 and 6 orders of magnitude higher than single domain α-In₂Se₃. Below 200 K, the transfer curves of T-T and H-H show gate-tunable p-type and n-type transport characteristics, respectively. The sheet resistance and mobility of H-H domain walls reaches 0.8 kΩ/sq and 15000 cm²/Vs at 5.5×10¹² cm^-2 carrier concentration and 120 K temperature. Using DFT, we attribute the enhanced conductivity and mobility to the presence of interfacial screening charges induced by opposite polarization.
The study lays the groundwork for precise control and understanding of the electronic properties of ferroelectric domain walls. Enhanced and gate-tunable domain wall conductance in a semiconductor system, as demonstrated here, will be useful for patterning nanocircuitries and realizing polarity-controlled transistors. Altogether, these findings will be useful to integrate domain walls as functional building blocks in memory, logic, interconnects, and neuromorphic computing applications.