S-Shaped Current-Voltage Characteristics of n+ - i - n - n+ Graphene Field-Effect Transistors due to the Coulomb Drag of Quasiequilibrium Electrons by Ballistic Electrons

We demonstrate that the injection of the ballistic electrons into the two-dimensional electron plasma in lateral ${n}^{+}$-$i$-$n$-${n}^{+}$ graphene field-effect transistors (GFETs) might lead to a substantial Coulomb drag of the quasiequilibrium electrons due the violation of the Galilean and Lorentz invariance in the systems with a linear electron dispersion. This effect can result in S-shaped current-voltage ($I$-$V$) characteristics. The resulting negative differential conductivity enables the hysteresis effects and current filamentation that can be used for the implementation of voltage-switching devices. Due to a strong nonlinearity of the $I$-$V$ characteristics, the GFETs can be used for an effective frequency multiplication and detection of terahertz radiation.