posted on 2014-01-22, 00:00authored byJong G. Ok, Jae Yong Lee, Hyoung Won Baac, Sameh H. Tawfick, L. Jay Guo, A. John Hart
We
investigate the rapid and anisotropic UV-induced photoconductive response
of hybrid thin films comprising zinc oxide (ZnO) nanowires (NWs) directly
grown on horizontally aligned (HA-) carbon nanotube (CNT) sheets.
The films exhibit anisotropic photoconductivity; along the CNTs, conductivity
is dominated by the CNTs and the photoconductive gain is lower, whereas
perpendicular to the CNTs the photoconductive gain is higher because
transport is influenced by ZnO nanoclusters bridging CNT-CNT contacts.
Because of the distributed electrical contact provided by the large
number of ZnO NWs on top of the HACNT film, this hybrid nanoarchitecture
has a significantly greater photocurrent than reported for single
ZnO NW-based devices at comparable UV illumination intensity. Moreover,
the hybrid architecture where a thin basal film of ZnO ohmically contacts
metallic CNTs enables rapid transport of photogenerated electrons
from ZnO to CNTs, resulting in sub-second photoresponse upon pulsed
illumination. The built-in potential generated across ZnO–CNT
heterojunctions competes with the externally applied bias to control
the photocurrent amplitude and direction. By tuning the anisotropic
conductivity of the CNT network and the morphology of the ZnO or potentially
other nanostructured coatings, this material architecture may be engineered
in the future to realize high-performance optical and chemical sensors.