On the current delivery limit of semiconducting carbon nanotubes

The current carrying capacity of single-walled semiconducting carbon nanotubes (CNTs) is studied by self-consistent quantum simulations using the non-equilibrium Green's function formalism with the self-consistent Born approximation. The simulation shows that the current carrying capacity depends on the bias regime and is drastically different from that of metallic tubes. For long CNTs (with a length much longer than zone boundary and optical phonon scattering mean free path), the current saturates around 20 mu A in the forward bias regime with unipolar transport due to phonon scattering. In ambipolar transport regime, the current delivery limit is still about 20 mu A due to recombination of electron and hole currents. In contrast, for short semiconducting CNTs, the current delivery capacity can be above 25 mu A in the unipolar transport regime and further double in the ambipolar transport regime. In reverse bias regime, the current of a long CNT can exceed 20 mu A due to the second subband conduction and increased electron injection from the drain. The simulation provides a coherent explanation to the dependence of current delivery limit on bias regime and channel length, which is consistent with recent experiments.