  Photoexcited intralayer excitons in van der Waals heterostructures (vdWHs)
with type-II band alignment have been observed to tunnel into interlayer
excitons on ultrafast timescales. Such interlayer excitons have sufficiently
long lifetimes that inducing dissociation with external in-plane electric
fields becomes an attractive option of improving efficiency of photocurrent
devices. In the present paper, we calculate interlayer exciton binding
energies, Stark shifts, and dissociation rates for six different transition
metal dichalcogenide (TMD) vdWHs using a numerical procedure based on exterior
complex scaling (ECS). We utilize an analytical bilayer Keldysh potential
describing the interaction between the electron-hole pair, and validate its
accuracy by comparing to the full multilayer Poisson equation. Based on this
model, we obtain an analytical weak-field expression for the exciton
dissociation rate. The heterostructures analysed are MoS$_2$/MoSe$_2$,
MoS$_2$/WS$_2$, MoS$_2$/WSe$_2$, MoSe$_2$/WSe$_2$, WS$_2$/MoSe$_2$, and
WS$_2$/WSe$_2$ in various dielectric environments. For weak electric fields, we
find that WS$_2$/WSe$_2$ supports the fastest dissociation rates among the six
structures. We, furthermore, observe that exciton dissociation rates in vdWHs
are significantly larger than in their monolayer counterparts.
