Efficient Gate Modulation in a Screening-Engineered MoS₂/Single-Walled Carbon Nanotube Network Heterojunction Vertical Field-Effect Transistor

In this report, a screening-engineered carbon nanotube (CNT) network/MoS₂/metal heterojunction vertical field effect transistor (CNT-VFET) is fabricated for an efficient gate modulation independent of the drain voltage. The gate field in the CNT-VFET transports through the empty space of the CNT network without any screening layer and directly modulates the MoS₂ semiconductor energy band, while the gate field from the Si back gate is mostly screened by the graphene layer. Consequently, the on/off ratio of CNT-VFET maintained 10³ in overall drain voltages, which is 10 times and 1000 times higher than that of the graphene (Gr) VFET at V_sd = 0.1 (ratio = 81.9) and 1 V (ratio = 3), respectively. An energy band diagram simulation shows that the Schottky barrier modulation of CNT/MoS₂ contact along the sweeping gate bias is independent of the drain voltage. On the other hand, the gate modulation of Gr/MoS₂ is considerably reduced with increased drain voltage because more electrons are drawn into the graphene electrode and screens the gate field by applying a higher drain voltage to the graphene/MoS₂/metal capacitor.