Use of graphene in optoelectronic devices as a transparent electrode
Suk-Ho Choi
Department of Applied Physics, Kyung Hee University, Yongin 17104, Korea
E-mail:
Tel: 82-31-201-2418, Fax: 82-31-204-8122
Graphene is currently being recognized as one of the candidates promising for its application
in transparent conducting electrodes (TCEs). In this talk, I’ll review our recent studies on the
use of graphene in the TCEs of optoelectronic devices such as photodetectors (PDs) and solar
cells. I introduce graphene-based vertical-junction diodes first developed in our group by
using solely graphene or its convergence structures and compare them with those of other
device structures. I discuss all-graphene p-n vertical tunneling junctions that were fabricated
by chemical vapor deposition and chemical treatment
.
One of the most important
characteristics of the graphene tunneling junctions is the asymmetric rectifying behavior
showing on/off ratio of
10
3
under bias voltages below ± 10 V without gating.
The observed
rectification results from the strongly-corrugated insulating/semiconducting interlayers,
graphene quantum dots (GQDs), or hybrid of GQDs/silica nanoparticles, sandwiched
between the doped or pristine graphene sheets, which is actually a structure like
metal-insulator-metal or metal-semiconductor-metal tunneling diode. These graphene-based
vertical-tunneling diodes show unique PD characteristics, which follow well what are
expected from their band structures. I also introduce first fabrication of graphene/Si quantum
dots (SQDs)-heterojunction tunneling diodes that work as PDs showing high performances
very sensitive to the variations in size of SQDs as well as in doping concentration of
graphene. I discuss the tunneling behaviors of the graphene/SQDs diodes and how the
graphene acts as a transparent electrode in the photovoltaic applications of the
graphene/SQDs diodes, depending on the annealing temperature and doping concentration of
the graphene on the devices. The I-V measurements demonstrate that the tunneling diodes
show temperature-dependent negative differential resistance in a voltage region, i.e.,
resonant-tunneling behaviors.
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