Sub-bands energy effect in the CNTFET chracteristics

Modeling of sub-band and diameter effect in carrier concentration of CNTFET

“…The increase of the drain current with respect to the diameter is directly associated with the decrease of the CNT band gap energy E g with its diameter. If the diameters of CNT increase, the band gap E g becomes small and the separation energy between the seconds and third sub-bands decreases [19]. Fig.…”

“…Due to the approximation of the graphene band structure and using the zone folding approximation in Eq. (5), the dispersion relation E(k) is [19] Eðk; qÞffi 7…”

“…This indicates that the carriers in the first sub-band are easier to move from valence to conduction band due to the smaller band gap compared to the other sub-bands. However, when the diameter increased, the band gap for the first, second and third sub-bands becomes too close and the passage of carrier becomes important [19]. Before the effect of sub-band on the carrier concentration, which indicates the number of occupied levels in the band energy per unit length, given in Eq.…”

“…Guo et al [21] have shown that up to two sub-bands are important in determining charge transport in practical CNT transistors. Moreover, when an electric potential is applied to the gate electrode, the nanotube energy levels are pushed down and the mobile charges are induced in the device [19][20][21]. Therefore more sub-bands will be participated in the drain current calculation and consequently the saturation drain current will be increased when more carriers are found on the higher bands.…”