Improving the ambipolar behavior of Schottky barrier carbon nanotube field effect transistors

Due to the capability of ballistic transport, carbon nanotube field-effect transistors (CNTFETs) have been studied in recent years as a potential alternative to CMOS devices. CNTFETs can be fabricated with ohmic or Schottky type contacts. We focus here on Schottky barrier CNTFETs which operate by modulating the transmission coefficient of Schottky barriers at the contact between the metal and the carbon nanotube (CNT). The ambipolar behavior of Schottky barrier CNTFETs limits the performance of these devices. We show that a double gate design can suppress the ambipolar behavior considerably. In this structure, for an n-type device, the first gate which is near the source controls electron injection and the second gate which is near the drain suppresses hole injection. The voltage of the second gate can be set to a constant voltage or to the drain voltage. We investigated the effect of the second gate voltage on the performance of the device and finally discuss the advantages and disadvantages of these designs.