AVS 51st International Symposium
    Nanometer-scale Science and Technology Monday Sessions
       Session NS-MoM

Paper NS-MoM6
Carbon Nanotube Photo-detectors

Monday, November 15, 2004, 10:00 am, Room 213D

Session: Carbon Nanotubes-Electrical Properties
Presenter: M.S. Marcus, University of Wisconsin-Madison
Authors: M.S. Marcus, University of Wisconsin-Madison
O.M. Castellini, University of Wisconsin-Madison
J.M. Simmons, University of Wisconsin-Madison
M.A. Eriksson, University of Wisconsin-Madison
Correspondent: Click to Email
We demonstrate two different nanotube device structures for use as photo-detectors: Bundle devices on quartz using photo-generated currents in the bundle, and transistor devices on Si/SiO@sub 2@ substrates that use photo-generated voltages in the substrate to provide a gating effect. The transistor devices are fabricated on SiO@sub 2@/p-Si substrates, where the p-Si is used as a gate for the nanotube channel. Light is absorbed by not only the carbon nanotube producing photocurrents, but also in the silicon gate that produces a photo-voltage at the interface between the Si/SiO@sub 2@. We observe that photo-voltages of ~15mV change the channel current by up to 1nA in the transistor. The small addition of the photo-voltage when the nanotube is illuminated by a modulated light source acts to probe the derivative of the channel current with respect to the gate voltage. When the laser illuminates at large distances from the nanotube we find that there are smaller but still measurable changes in the channel current, indicating that the carriers responsible for photo-gating are mobile. In order to isolate the nanotube-light interaction from the silicon gate, we have fabricated nanotube bundle devices on transparent quartz substrates. We measure a variety of response times, some of which are surprisingly slow sometimes taking ~8ms to transition from a light off to on state. We propose that inter-tube coupling plays a role in the long response times, and present a model of why it can take photo-generated carriers a long time to be extracted as photocurrent.