Performance of Zero-Schottky-Barrier and Doped Contacts Single and Double Walled Carbon Nanotube Transistors

Atomistic quantum simulation is performed to compare the performance of single walled (SW) and double walled (DW) carbon nanotube field effect transistors (CNTFETs) with two different types of contacts: zero-Schottky-barrier (SB) contacts and doped (DP) contacts. Both the DW and SW CNTFETs have better performance with doped contacts. The conduction band under the gate region is pushed down below the source Fermi level when the applied gate bias is ${\geq} E_{\text{g}}/2$. Beyond this gate voltage, the current in SB CNTFETs becomes almost constant. This does not happen to the doped contacts devices and they have better on-state performance. With the same type of contacts, the SW and DW CNTFETs exhibit similar $I$–$V$ characteristics. However, the switching delay and the unity current gain frequency are much better in DW CNTFETs for both types of contacts. The better switching performance of DW CNTFETs results from the smaller gate capacitance. ©2010

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