Ambipolar to Unipolar Conversion in Graphene Field-Effect Transistors

Abstract

Typical graphene field-effect transistors (GFETs) show ambipolar conduction that is unfavorable for some electronic applications. In this work, we report on the development of unipolar GFETs. We found that the titanium oxide situated on the graphene surface induced significant hole doping. The threshold voltage of the unipolar p-type GFET was tunable by varying the density of the attached titanium oxide through an etching process. An annealing process followed by silicon nitride passivation was found to convert the p-type GFETs to unipolar n-type GFETs. An air-stable complementary inverter integrated from the p- and n-GFETs was also successfully demonstrated. The simple fabrication processes are compatible with the conventional CMOS manufacturing technology.

Controlled charge trapping by molybdenum disulphide and graphene in ultrathin heterostructured memory devices

“…4a. Similar unipolar behaviour was reported in graphene covered with water layer or in doped graphene by metallic oxide, and graphene dual dielectric memory 23,35,36 . To verify that the unipolar behaviour is due to charge trapping in the MoS 2 layer, we employed two devices fabricated on a same graphene flake without MoS 2 -trapping layer, but one on hBN (GB2) and the other on SiO 2 (GS2) (Supplementary Fig.…”

Back-gate graphene field-effect transistors with double conductance minima

“…5. The above assumptions can be proved by the experimental results in our study and in previous publications [17,18]. According to Fig.…”

“…2(a), it can be inferred that the graphene is n-doped for the negative shift of the charge neutrality point. On the other hand, Ti has been demonstrated to serve as a p-type dopant for graphene [17,18]. Therefore, the graphene p-n junction is formed between the graphene under the metal contact and in the channel area, and consequently gives rise to the Wshape r-V g curve with double local conductance minima.…”

A Study on Graphene—Metal Contact

“…Note that there is possible carbide formation after Ti deposition onto the graphene, similar to surface-carbide formation in additional Ni deposition on graphene [45]. However, the number of Ti-C bonds is very low and their influence on electron transport is negligible [46]. It was also observed that the significant increase in D band sputtered Al/SLG, Al/DLG contacts, asshown in Figure 6.…”