Hybrid devices consisting of graphene
or transition metal dichalcogenides
(TMDs) and semiconductor quantum dots (QDs) were widely studied for
potential photodetector and photovoltaic applications, while for photodetector
applications, high internal quantum efficiency (IQE) is required for
photovoltaic applications and enhanced carrier diffusion length is
also desirable. Here, we reported the electrical measurements on hybrid
field-effect optoelectronic devices consisting of compact QD monolayer
at controlled separations from single-layer graphene, and the structure
is characterized by high IQE and large enhancement of minority carrier
diffusion length. While the IQE ranges from 10.2% to 18.2% depending on QD-graphene separation, d
s, the carrier diffusion length, L
D, estimated from scanning photocurrent microscopy (SPCM)
measurements, could be enhanced by a factor of 5–8 as compared
to that of pristine graphene. IQE and L
D could be tuned by varying back gate voltage and controlling the
extent of charge separation from the proximal QD layer due to photoexcitation.
The obtained IQE values were remarkably high, considering that only
a single QD layer was used, and the parameters could be further enhanced
in such devices significantly by stacking multiple layers of QDs.
Our results could have significant implications for utilizing these
hybrid devices as photodetectors and active photovoltaic materials
with high efficiency.