  The possibility of electrical manipulation and detection of charged exciton
(trion) before its radiative recombination makes it promising for excitonic
devices. Using a few-layer graphene/monolayer WS$_{2}$/monolayer graphene
vertical heterojunction, we report inter-layer charge transport from top
few-layer graphene to bottom monolayer graphene, mediated by coherently formed
trion state. This is achieved by using a resonant excitation and varying the
sample temperature, the resulting change in the WS$_{2}$ bandgap allows us to
scan the excitation around the exciton-trion spectral overlap with high
spectral resolution. By correlating the vertical photocurrent and in situ
photoluminescence features at the heterojunction as a function of the spectral
position of the excitation, we show that (1) trions are anomalously stable at
the junction even up to 463 K due to enhanced doping, and (2) the photocurrent
results from the ultra-fast formation of trion through exciton-trion coherent
coupling, followed by its fast inter-layer transport. The demonstration of
coherent formation, high stabilization, vertical transportation and electrical
detection of trions marks a step towards room temperature trionics.
