Improved Transfer of Graphene for Gated Schottky-Junction, Vertical, Organic, Field-Effect Transistors

Abstract

An improved process for graphene transfer was used to demonstrate high performance graphene enabled vertical organic field effect transistors (G-VFETs). The process reduces disorder and eliminates the polymeric residue that typically plagues transferred films. The method also allows for purposely creating pores in the graphene of a controlled areal density. Transconductance observed in G-VFETs fabricated with a continuous (pore-free) graphene source electrode is attributed to modulation of the contact barrier height between the graphene and organic semiconductor due to a gate field induced Fermi level shift in the low density of electronic-states graphene electrode. Pores introduced in the graphene source electrode are shown to boost the G-VFET performance, which scales with the areal pore density taking advantage of both barrier height lowering and tunnel barrier thinning. Devices with areal pore densities of 20% exhibit on/off ratios and output current densities exceeding 10(6) and 200 mA/cm(2), respectively, at drain voltages below 5 V.

Gate‐Controlled Energy Barrier at a Graphene/Molecular Semiconductor Junction

“…This is mainly caused by the large DOS in conventional metals, which requires an exceedingly large amount of induced charges to modulate their Fermi-level. [ 14 ] Figure 3 d shows the current-voltage ( I DS -V DS ) characteristics of both graphene/C 60 /Al and graphene/C 60 /Cu devices, in the dark and without applying any V GS . As indicated above, the diodes are considered to be in forward bias when a negative V DS is applied, i.e., electrons are being injected from the LUMO level of C 60 to graphene whereas a positive V DS changes the diode operation into reverse bias condition.…”

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wileyonlinelibrary.comGraphene, [ 11 ] a one-atom thick zero band gap semiconductor has allowed the development of new electronic device schemes such as the graphene-barristor, [ 12 ] the graphene-vertical-fi eld-effecttransistor (VFET), [13][14][15][16] and the graphenebase hot electron transistor. [ 17 ] In organic electronics, graphene can be an ideal choice to use as the injector (or source) electrode for a VFET since its Fermi level, its corresponding work function and its available low density of states (DOS) [ 18 ] can all be easily modulated, providing a tunable energy barrier which eventually controls the device operation.

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“…Graphene, similar to carbon nanotubes in its electrical and mechanical properties, has additional advantages over them due to the large-scale availability (chemical vapor deposition (CVD)-grown graphene) of chemically inert high quality 2D surfaces. [ 14,22 ] On the other hand, fullerene (C 60 ) is one of the most widely studied molecular semiconductors [ 2,5,20,[23][24][25] and a common choice as an active media for transistors. C 60 has an energy gap ( E g = 1.7 eV), between its highest occupied molecular orbital…”

Direct Determination of Field Emission across the Heterojunctions in a ZnO/Graphene Thin-Film Barristor

“…These TFTs operate through the formation of a channel with a high density of charge carriers induced by a gate bias. However, we believe that the unique switching characteristic of our device originates from current passing across a series of ZnO/graphene heterojunctions, as in graphene barristors 2,7 . In graphene barristors, a gate bias is used to modulate graphene's work function, which is directly linked to the height of SB.…”

“…In graphene barristors, a gate bias is used to modulate graphene's work function, which is directly linked to the height of SB. 8,9 The barrier height and the current across it follow a reverse exponential relationship under thermionic emission (TE) where thermal energy excites charge carriers over the SB ( Table 1) 2,7 . This allows for the high on/off ratios achieved in graphene barristors (e.g.…”