Ferroelectric control of the semiconductor-metal transition in two-dimensional $M{\mathrm{Si}}_2{P}_4$/${\mathrm{Sc}}_2{\mathrm{CO}}_2$ ($M$= $\mathrm{Mo}$, $W$) van der Waals heterostructures and application to nonvolatile memory devices

The integration of two-dimensional (2D) ferroelectrics with other materials holds immense significance for exploring physics at the nanoscale. In this work, we systematically investigate the electronic and transport properties of 2D ${\mathrm{Mo}\mathrm{Si}}_2{P}_4$/${\mathrm{Sc}}_2{\mathrm{CO}}_2$ and ${\mathrm{WSi}}_2{P}_4$/${\mathrm{Sc}}_2{\mathrm{CO}}_2$ ferroelectric van der Waals heterostructures using density-functional theory and the nonequilibrium Green function method. The results reveal that the semiconductor-metal transition of ${\mathrm{Mo}\mathrm{Si}}_2{P}_4$ and ${\mathrm{WSi}}_2{P}_4$ monolayers can be flexibly realized by switching the ferroelectric polarization of the ${\mathrm{Sc}}_2{\mathrm{CO}}_2$ monolayer. Moreover, the metallicity of ${\mathrm{Mo}\mathrm{Si}}_2{P}_4$ and ${\mathrm{WSi}}_2{P}_4$ monolayers is further enhanced as the thickness of the ferroelectric layer increases, and the clamped sandwich structure also allows the nonvolatile electrical control of the metallicity of these two materials. Accordingly, proof-of-concept diodes based on ${\mathrm{Mo}\mathrm{Si}}_2{P}_4$/${\mathrm{Sc}}_2{\mathrm{CO}}_2$ and ${\mathrm{WSi}}_2{P}_4$/${\mathrm{Sc}}_2{\mathrm{CO}}_2$ heterostructures exhibit giant current on:off ratios of up to ${10}^6$ and ${10}^5$, respectively. These findings not only provide viable strategies to realize and control metallicity in 2D semiconductors, but also offer promising candidates for the design of advanced memories.