Imaging transport in nanowires using near-field detection of light

Abstract

Major progress in the crystal growth of nanowires and related structures places new demands on our abilities to characterize optical and electronic properties with both an ease and a resolution commensurate with the materials of interest. In particular, transport properties, such as minority carrier diffusion length, are important for a range of applications in light emission, sensing and solar energy conversion. In this paper, a technique to "image transport" in nanostructures by monitoring the motion of charge via the recombination emission of light is reviewed. Transport imaging combines the resolution of near-field optics with the charge generation control of a scanning electron microscope. The technique is related to, but significantly different from standard cathodoluminescence, since it maintains the spatial information of the emitted light. Light is collected in the near-field from a scanning fiber in an atomic force microscope/near-field scanning optical microscope system. It is possible to determine minority carrier or exciton diffusion lengths from a single optical image, without any electrical contact to the sample. New results are presented for minority carrier hole transport in ZnO nanowires and nonobelts.