Spectroscopy of strongly localized excitons and band-gap states in semiconducting single-walled carbon nanotubes

It is often assumed that single-walled carbon nanotubes grown via catalytic chemical vapor deposition are free of defects, particularly when suspended over a trench. Here we show that semiconducting nanotubes grown in this manner can contain a surprisingly large number of states within the band gap. High-resolution photocurrent spectroscopy is used to probe these states in individual nanotubes. We observe a series of band-gap states in suspended nanotubes, resulting in long trapping and detrapping times. These states significantly alter the exciton spectra, resulting in a manifold of strongly localized exciton states with narrow linewidths (<1 meV at room temperature) within a broader exciton envelope.