Abstract
By pretreating the substrate of a graphene field-effect transistor (G-FET), a stable unipolar transfer characteristic, instead of the typical V-shape ambipolar behavior, has been demonstrated. This behavior is achieved through functionalization of the SiO2/Si substrate that changes the SiO2 surface from hydrophilic to hydrophobic, in combination with postdeposition of an Al2O3 film by atomic layer deposition (ALD). Consequently, the back-gated G-FET is found to have increased apparent hole mobility and suppressed apparent electron mobility. Furthermore, with addition of a top-gate electrode, the G-FET is in a double-gate configuration with independent top- or back-gate control. The observed difference in mobility is shown to also be dependent on the top-gate bias, with more pronounced effect at higher electric field. Thus, the combination of top and bottom gates allows control of the G-FET’s electron and hole mobilities, i.e., of the transfer behavior. Based on these observations, it is proposed that polar ligands are introduced during the ALD step and, depending on their polarization, result in an apparent increase of the effective hole mobility and an apparent suppressed effective electron mobility.
Highlights
The lack of a proper bandgap in graphene has prevented its serious consideration for use in fieldeffect devices so far
The graphene-based field-effect transistor (G-FET) was one of the first devices to be manufactured in the original study in 2004.1 The G-FET is a suitable platform for evaluation and comparison of electronic behaviors, processes, and different methods or dopants.[2,3]
Graphene was produced by chemical vapor deposition (CVD) on Cu-foil substrate with Ar:H2:CH4 feed gases mixed at ratio of 100:75:1
Summary
The lack of a proper bandgap in graphene has prevented its serious consideration for use in fieldeffect devices so far. One specific category of interfacial additives are those of polar nature Such additives have been shown to have a great effect on the mobility of the G-FET when in the vicinity of the graphene.[4]. Introducing bis(trimethylsilyl)amine (HMDS), a known surfactant for increasing the hydrophobicity of the SiO2 surface, prior to transfer of the graphene will greatly affect the ability of the ALD process to deposit a high-quality film of Al2O3. This change of the substrate wettability is here shown to alter the Al2O3 film properties and thereby efficiently affect the ambipolar behavior of the G-FET and increase the effective hole mobility. G-FETs are studied both without a top gate (showing the most pronounced elevation/suppression of mobility) and with a top gate covering the channel
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