Near-field scanning photocurrent microscopy of a nanowire photodetector

A near-field scanning optical microscope was used to image the photocurrent induced by local illumination along the length of a metal-semiconductor-metal (MSM) photodetector made from an individual CdS nanowire. Nanowire MSM photodetectors exhibited photocurrents similar to 10(5) larger than the dark current (< 2 pA) under uniform monochromatic illumination; under local illumination, the photoresponse was localized to the near-contact regions. Analysis of the spatial variation and bias dependence of the local photocurrent allowed the mechanisms of photocarrier transport and collection to be identified, highlighting the importance of near-field scanning photocurrent microscopy to elucidating the operating principles of nanowire devices. (c) 2005 American Institute of Physics.