Abstract
A band gap is opened in bilayer graphene (BLG) by applying an electric field perpendicular to the layer, which offers versatility and controllability in graphene-based electronics. The presence of the band gap has been confirmed using double-gated BLG devices in which positive and negative gate voltages are applied to each side of BLG. An alternative method to induce the electric field is electron and hole doping of each side of BLG using electron-transfer adsorbates. However, the generation of the band gap by carrier doping is still under investigation. Here, we determined whether the electron/hole doping can produce the electric field required to open the band gap by measuring the temperature dependence of conductivity for BLG placed between electron-donor self-assembled monolayers (SAMs) and electron-acceptor molecules. We found that some devices exhibited a band gap and others did not. The potentially irregular and variable structure of SAMs may affect the configuration of the electric field, yielding variable electronic properties. This study demonstrates the essential differences between gating and doping.
Highlights
Control of carrier density is a key issue when engineering the electronic properties of materials
A notable example is bilayer graphene (BLG), which has two quasi-quadratic bands in contact with each other. This zero-gap semiconductor exhibits a band gap when it was subjected to a perpendicular electric field[18], which was confirmed from transport and optical properties[19,20,21] for a double-gated field-effect transistor (FET) structure
The molecular density of SAMs33, i.e., the number of NH2-alkylsilane (NH2-AS) per unit area is typically (1–2) × 1014 cm−2, while the electron density transferred from NH2-self-assembled monolayers (SAMs) is estimated to be 5 × 1012 cm−2 as described before
Summary
Control of carrier density is a key issue when engineering the electronic properties of materials. A notable example is bilayer graphene (BLG), which has two quasi-quadratic bands in contact with each other This zero-gap semiconductor exhibits a band gap when it was subjected to a perpendicular electric field[18], which was confirmed from transport and optical properties[19,20,21] for a double-gated FET structure. The double-doping method (or electron/hole doping) is expected to give the same effect in BLG as the double-gating, the mechanism that produces the electric field is completely different. The electronic property of doped BLG has been studied in several experiments far[27,28,29,30], and the presence of a band gap is confirmed in some reports[27, 28].
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