**4.2. Metallic doping by source drain contacts in graphene**

Graphene is a self-contained electronic sheet showing no classical band bending interactions when coupled to a metallic contact as shown in Figure 18. This creates an abrupt transition in the vacuum level, creating a barrier that any carrier would have to tunnel through, creating charge buildup at the band edges and large contact resistances. [56]

**Figure 18.** Classical band diagrams for a metal-silicon interface, a metal-metal interface, and a metal graphene inter‐ face.

In conjunction to this challenge is the relative inertness of a graphene sheet, making good electrical contacts difficult to realize and mainly occurring at grain edges. [56] This creates a situation where the bulk of the contact sits over the graphene electrostatically doping it, while also trying to realize good adhesion creating a search for a metals with good adhesion to graphene along with the correct Fermi level. [56] To achieve this goal, a double or triple metal stack is commonly used with an oxygen scavenger interfacing the graphene (normally Ti), followed by one or a couple of Fermi level contacts (Au, Pd, Ni). [56] The metallic doping effect, however, can be utilized for some interesting devices such as one using asymmetric contacts to create an internal electric field making an IR detector through the photothermoelectric effect, or using large gap superconducting contacts to confine electrons and holes in a graphene sheet to enhance bolometric response. [45, 57]

### **4.3. Dielectric deposition and trap states**

As stated in Section 1 and Section 3, graphene is a self-contained layer without any dangling bonds, thus adhesion and interfaces with graphene are a challenge. Multiple groups have been experimenting with different types of oxides with either an aluminum deposition and oxidation or a nitrogen dioxide surface pretreatment prior to a hafnium oxide, silicon dioxide, or aluminum oxide deposition. [58] The dielectric which seems to work the best (but has not yet been implemented in a complementary metal oxide semiconductor (CMOS) fabrication process) is another 2D self-contained dielectric BN with which graphene has shown mobilities of 140,000 cm2 /Vs, which is very close to completely suspended graphene grown from a SiC step edge, demonstrating low interaction and good isolation between the two substrates. [42]
