Center for Functional Nanomaterials Seminar

Semiconductor nanowires are being considered as novel functional components for nanoelectronics, but quantitative measurements of critical material properties are not abundant. This is due in part to the challenge of identifying and/or adapting characterization techniques that are suitable for these highly scaled devices. The realization of reliable nanowire device technology can therefore be facilitated by the development of techniques to quantify fundamental metrics including carrier mobility, diffusion, and lifetime. Scanning probe techniques are well suited to the study of properties in nanoscale materials as they provide high spatial resolution, low sampling volume, and high sensitivity. Two such techniques and their application to semiconductor nanowire characterization will be discussed: electron-beam induced current (EBIC) and scanning photocurrent microscopy (SPCM). In each case, a focused beam of energetic particles is used to locally excite an excess carrier population in a nanowire device while the induced change in current is monitored as a function of the beam position. The resulting induced current map can be used to separate the electrical properties of the nanowires from the overall device characteristics. The influence of the metal contacts and compositional and morphological inhomogeneities on device characteristics can also be identified and will be discussed. Quantitative determination of minority carrier diffusion lengths in n-type silicon nanowires have been used to show that minority carrier transport is dominated by surface recombination in wires with diameters as large as 100 nm. This result along with detailed compositional analysis has been used to address the long-standing question of catalyst contamination in Au-catalyzed vapor-liquid-solid nanowire growth (1).


1 J. E. Allen, E. R. Hemesath, et al. Nature Nanotechnology 3, 168-173(2008).