Effect of Scattering on Carbon Nanotube Field Effect Transistor Characteristics

Carbon nanotubes (CNTs) have been extensively explored for nanoelectronic applications due to their excellent electrical properties. We use the field effect transistor in witch the carrier channel is replaced with the carbon nanotube . This device is simulated by solving coupled Poisson and Schrodinger equations. Non-equilibrium Green’s function (NEGF) method is used to investigate the transport properties[1]. The uncoupled mode space approach is used to reduce the computational burden. Scattering plays an important role on carrier transport and I-V characteristics of CNTs. It is demonstrated that under low biases, the dominant scattering mechanism in a high-quality CNT is the near-elastic acoustic phonon (AP) scattering with a mean free path mfp of ~1μm. Due to the long mfp, near-ballistic transport can be readily achieved for CNTs with submicron-meter lengths. Under high biases, The most important scattering mechanism is the short-mfp of 10 nm optical phonon(OP) scattering. Because a channel length of 10 nm or above is preferred for controlling the short-channel effects and preventing the source-drain tunneling. OP scattering is expected to dominate even in a short-channel carbon nanotube field effect transistor(CNTFET). As the channel length of the CNTFETs is being aggressively scaled below 100 nm for potential nanoelectronic device applications, it is important to clearly understand the role of phonon scattering in shortchannel CNTFETs. A recent work using semiclassical simulations showed that OP scattering has a very small direct effect on the dc (on current) under modest gate biases[2].Also a quantum mechanical treatment of scattering in planar geometry of CNTFET is investigated[3]. In this paper we study the effect of scattering on coaxially gated CNTFET characteristic that channel length is changed and also effect of change in length between gate and drain and effect of change in doping region. In this work, a quantum treatment of phonon scattering in CNTFETs using the nonequilibrium Green’s function (NEGF) formalism with the self-consistent Born approximation is presented[4]. For a CNTFET with a one dimensional channel, the approach is physically much more rigorous than and computationally as efficient as a phenomenological treatment of scattering using the Büttiker probe approach, which has been widely used in mesoscopic physics.