Photocurrent Measurements of Carbon Nanotube PN Junctions

Gated p-n junctions in semiconducting nanotubes have recently drawn much attention for their electronic and optoelectronic characteristics [1,2,3]. We investigate the photocurrent response at a nanotube gated p-n junction using a focused laser illumination source. We find that the photocurrent at zero source-drain bias increases linearly with optical power for the component of light along the length of the nanotube. Scanned photocurrent imaging demonstrates that carrier generation occurs primarily between the p- and n- type segments of the device. Measurements in an optical cryostat down to 4K reveal large photoresponse and step-like structure in the reverse bias photocurrent. These results show that nanotube p-n junctions are highly sensitive, nanoscale photodetectors. [1] J.U. Lee et al, App. Phys. Lett. \textbf{85}, 145 (2004). [2] J.U. Lee, App. Phys. Lett. \textbf{87}, 073101 (2005). [3] K. Bosnick et al, App. Phys. Lett. \textbf{89}, 163121 (2006).