  Ferroelectric tunnel junctions, in which ferroelectric polarization and
quantum tunneling are closely coupled to induce the tunneling electroresistance
(TER) effect, have attracted considerable interest due to their potential in
non-volatile and low-power consumption memory devices. The ferroelectric size
effect, however, has hindered ferroelectric tunnel junctions from exhibiting
robust TER effect. Here, our study proposes doping engineering in a
two-dimensional in-plane ferroelectric semiconductor as an effective strategy
to design a two-dimensional ferroelectric tunnel junction composed of
homostructural $p$-type semiconductor/ferroelectric/$n$-type semiconductor.
Since the in-plane polarization persists in the monolayer ferroelectric
barrier, the vertical thickness of two-dimensional ferroelectric tunnel
junction can be as thin as monolayer. We show that the monolayer
In:SnSe/SnSe/Sb:SnSe junction provides an embodiment of this strategy.
Combining density functional theory calculations with non-equilibrium Green's
function formalism, we investigate the electron transport properties of
In:SnSe/SnSe/Sb:SnSe and reveal a giant TER effect of 1460$\%$. The dynamical
modulation of both barrier width and barrier height during the ferroelectric
switching are responsible for this giant TER effect. These findings provide an
important insight towards the understanding of the quantum behaviors of
electrons in materials at the two-dimensional limit, and enable new
possibilities for next-generation non-volatile memory devices based on flexible
two-dimensional lateral ferroelectric tunnel junctions.
