In this paper the device characteristics and performance of n-i-n and p-i-n carbon nanotube field-effect transistors (CNTFETs) are compared and investigated. The simulations have been performed by the self-consistent solution of 2-D Poisson–Schrodinger equations, within the nonequilibrium Green’s function (NEGF) formalism. p-i-n CNTFETs acts based on tunneling mechanism while n-i-n CNTFETs carrier transfer is mainly due to thermionic mechanism above the channel barrier. The comparisons are done in terms of ON current, OFF current, ON/OFF current ratio, and subthreshold swing at equal simulation conditions. Two gate all around CNTFETs with n-type and p-type source regions have been simulated and compared at the same physical parameters and bias conditions. Our simulations show that n-i-n structure has higher saturation current, lower leakage current and consequently higher current ratio than their p-i-n counterpart. But, the p-i-n results in better subthreshold swing parameter at subthreshold regime in comparison with n-i-n structures
