Among the family
of 2D materials, graphene is the ideal
candidate
as top or interlayer electrode for hybrid van der Waals heterostructures
made of organic thin films and 2D materials due to its high conductivity
and mobility and its inherent ability of forming neat interfaces without
diffusing in the adjacent organic layer. Understanding the charge
injection mechanism at graphene/organic semiconductor interfaces is
therefore crucial to develop organic electronic devices. In particular,
Gr/C60 interfaces are promising building blocks for future n-type
vertical organic transistors exploiting graphene as tunneling base
electrode in a two back-to-back Gr/C60 Schottky diode configuration.
This work delves into the charge transport mechanism across Au/C60/Gr
vertical heterostructures fabricated on Si/SiO2using a
combination of techniques commonly used in the semiconductor industry,
where a resist-free CVD graphene layer functions as a top electrode.
Temperature-dependent electrical measurements show that the transport
mechanism is injection limited and occurs via Fowler–Nordheim
tunneling at low temperature, while it is dominated by a nonideal
thermionic emission at room and high temperatures, with energy barriers
at room temperature of ca. 0.58 and 0.65 eV at the Gr/C60 and Au/C60
interfaces, respectively. Impedance spectroscopy confirms that the
organic semiconductor is depleted, and the energy band diagram results
in two electron blocking interfaces. The resulting rectifying nature
of the Gr/C60 interface could be exploited in organic hot electron
transistors and vertical organic permeable-base transistors.