  Hybrid graphene photoconductor/phototransistor has achieved giant
photoresponsivity, but its response speed dramatically degrades as the expense
due to the long lifetime of trapped interfacial carriers. In this work, by
intercalating a large-area atomically thin MoS2 film into a hybrid graphene
photoconductor, we have developed a prototype tunneling photoconductor, which
exhibits a record-fast response (rising time ~17 ns) and a high responsivity
(~$3\times10^4$ A/W at 635 nm and 16.8 nW illumination) across the broad
spectral range. We demonstrate that the photo-excited carriers generated in
silicon are transferred into graphene through a tunneling process rather than
carrier drift. The atomically thin MoS2 film not only serves as tunneling layer
but also passivates surface states, which in combination delivers a superior
response speed (~3 order of magnitude improved than a device without MoS2
layer), while the responsivity remains high. This intriguing tunneling
photoconductor integrates both fast response and high responsivity and thus has
significant potential in practical applications of optoelectronic devices.
