  We demonstrate a graphene-MoS2 architecture integrating multiple field-effect
transistors and we independently probe and correlate the conducting properties
of van der Waals coupled graphene-MoS2 contacts with the ones of the MoS2
channels. Devices are fabricated starting from high-quality single-crystal
monolayers grown by chemical vapor deposition and characterized by scanning
Raman and photoluminescence spectroscopies. Transconductance curves of MoS2 are
compared with the current-voltage characteristics of graphene contact stripes,
revealing a significant suppression of transport on the n-side of the
transconductance curve. Based on ab-initio modeling, the effect is understood
in terms of trapping by sulfur vacancies, which counter-intuitively depends on
the field-effect, even though the graphene contact layer is positioned between
the backgate and the MoS2 channel.
