Non‐Volatile Photochemical Gating of an Epitaxial Graphene/Polymer Heterostructure

Abstract

Electronic devices using epitaxial graphene on Silicon Carbide require encapsulation to avoid uncontrolled doping by impurities deposited in ambient conditions. Additionally, interaction of the graphene monolayer with the substrate causes relatively high level of electron doping in this material, which is rather difficult to change by electrostatic gating alone.Here we describe one solution to these problems, allowing both encapsulation and control of the carrier concentration in a wide range. We describe a novel heterostructure based on epitaxial graphene grown on silicon carbide combined with two polymers: a neutral spacer and a photoactive layer that provides potent electron acceptors under UV light exposure. Unexposed, the same double layer of polymers works well as capping material, improving the temporal stability and uniformity of the doping level of the sample. By UV exposure of this heterostructure we controlled electrical parameters of graphene in a noninvasive, non-volatile, and reversible way, changing the carrier concentration by a factor of 50. The electronic properties of the exposed SiC/ graphene/polymer heterostructures remained stable over many days at room temperature, but heating the polymers above the glass transition reversed the effect of light.The newly developed photochemical gating has already helped us to improve the robustness (large range of quantizing magnetic field, substantially higher opera-tion temperature and significantly enhanced signal-to-noise ratio due to significantly increased breakdown current) of a graphene resistance standard to

Nonequilibrium mesoscopic conductance fluctuations as the origin of 1/f noise in epitaxial graphene

“…Stable and lowresistance contacts (<10 in the quantum Hall regime) were fabricated by an optimized two-step metallization process, Ti/Au (10 nm/30 nm) followed by Au (50 nm), which enables direct contact between the second gold layer and the graphene edge [33]. Photochemical gating [34] was applied to reduce the charge-carrier concentration by covering the sample with two polymers (70 nm of poly(methyl methacrylate) [PMMA] resist followed by 300 nm of ZEP520A resist) and subsequent ultraviolet (UV) radiation at room temperature. The main results were confirmed on three different devices.…”

Weak localization scattering lengths in epitaxial, and CVD graphene

“…Photochemical gating was used to control the carrier density on the epitaxial devices due to the impossibility of conventional backgating through SiC. 15 CVD graphene was grown on thin-film copper, subsequently transferred to Si/SiO 2 , and contacts were made using chromegold tracks / bond pads followed by gold-only final contacting, as described in our previous work. 13 Various sizes of largearea Hall bar were produced; dimensions were typically 64 × 16 μm 2 for the CVD devices, and 160 × 35 μm 2 for the epitaxial devices.…”

Graphene nanogap for gate-tunable quantum-coherent single-molecule electronics

“…10 In a wide perspective, graphene is a material with potential as a versatile and controllable bridge between the atomic and the micron scales, with unique opportunities for nanoelectronics applications. Chemistry tools may alter graphene properites either globally (for example, chemical gating) 11 or locally (atoms and molecules bound to graphene). 12,13 At the same time, modern lithographic techniques compatible with semiconducting technology can be used to pattern graphene into devices and integrate them with conventional electronics.…”