| Single-Wall carbon nanotubes (SWCNTs) are promising for use in solar cells and photodetectors because of their strong optical absorption in most of the solar spectrum. There have been many reports about the photovoltaic effect in nanoelectronic devices based on individual SWCNTs, but they have been limited by complicated fabrication and miniscule absorption. Here we report the photovoltage (PV) and photocurrent (PC) in an easily fabricated macroscopic SWCNT film with a p-n junction, and we attribute these phenomena to the photothermoelectric (PTE) effect. Various factors affecting the PV amplitude and response time were studied, including the junction length, substrate, and doping level. We observed a maximal responsivity of ~1 V/W with SWCNTs on Teflon tape, and a fast response time of ~80 micros with SWCNTs on AlN substrates. We found that there exists a tradeoff between responsivity and response time based on the choice of substrate. It was found that the PV depended nonlinearly on the n-doping concentration, indicating the existence of an optimal doping level. Finally, we checked the photoresponse in a wide wavelength range (360--900 nm), and the PV was observed throughout, indicating that the device could potentially be used as a broadband photodetector. |
