Graphene-semiconductor Schottky diodes for new-generation field-effect transistors.

Graphene forms a Schottky junction (SJ) with many conventional semiconductors because its semimetal nature. The graphene-semiconductor SJ have been used to fabricate solar cells and photodetectors. However, they can also be used to modulate the conductivity of the channel of a graphene-semiconductor field-effect transistor (FET). This contribution will discuss the characterization of the SJ between graphene and the following three n-type semiconductors: Ge, Si, and GaAs. We will also demonstrate that the graphene-GaAs SJ can be used as a gate of a FET. This FET exploits the possibility of adjusting the graphene work function by an additional control gate stack fabricated on top of the graphene gate. A change of the graphene work function results in the modulation of the graphene-GaAs Schottky barrier height (SBH) and, therefore, the threshold voltage ($V_{th}$) of the FET. We used the modulation of the SBH to realize FETs that can be converted from the depletion mode FETs (with a negative $V_{th}$), into the enhancement mode FETs (with a positive $V_{th}$). This allowed the fabrication of digital logic gates with a positive switching threshold, which is needed for realizing integrated circuits.