Efficient conversion of photons into electrical current in two-dimensional
semiconductors requires, as a first step, the dissociation of the strongly
bound excitons into free electrons and holes. Here we calculate the
dissociation rates and energy shift of excitons in monolayer MoS2 as a
function of an applied in-plane electric field. The dissociation rates are
obtained as the inverse lifetime of the resonant states of a two-dimensional
hydrogenic Hamiltonian which describes the exciton within the Mott-Wannier
model. The resonances are computed using complex scaling, and the effective
masses and screened electron-hole interaction defining the hydrogenic
Hamiltonian are computed from first principles. For field strengths above 0.1
V/nm the dissociation lifetime is shorter than 1 ps, which is below the
lifetime associated with competing decay mechanisms. Interestingly,
encapsulation of the MoS2 layer in just two layers of hexagonal boron nitride
(hBN), enhances the dissociation rate by around one order of magnitude due to
the increased screening. This shows that dielectric engineering is an
effective way to control exciton lifetimes in two-dimensional materials
