  2D Ferroelectric materials are promising for designing low-dimensional memory
devices. Here, we explore strain tunable ferroelectric properties of group-IV
monochalcogenides MX (M=Ge, Sn; X=S, Se) and their potential application in
lateral field tunnel junction devices. We find that these monolayers have
in-plane ferroelectricity, with their ferroelectric parameters being on par
with other known 2D ferroelectric materials. Amongst SnSe, SnS, GeSe, and GeS,
we find that GeS has the best ferroelectric parameters for device applications,
which can be improved further by applying uniaxial tensile strain. We use the
calculated ferroelectric properties of these materials to study the tunneling
electroresistance (TER) of a 4 nm device based on lateral ferroelectric tunnel
junction. We find a substantial TER ratio $10^3-10^5$ in the devices based on
these materials, which can be further improved up to a factor of 40 on the
application of tensile strain.
