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In this invited contribution at the 29th International Conference on the Physics of semiconductors (ICPS 2008), we review two examples of solid-catalytic nanowire (NW) growth in parallel comparisons to the NW growth from the eutectic liquid catalyst. First, we demonstrated the Cu-catalyzed Ge NW growth using GeH4 vapor precursor at 200 °C, which is far below the Cu–Ge eutectic temperature of 644 °C, with a relatively uniform diameter distribution directly templated from that of the catalysts. We provide evidence that the formation of solid Cu3Ge catalysts and Ge diffusion across the catalysts are responsible for such low-temperature growth of Ge NWs in a size-deterministic manner. Second, we show the spontaneous silicidation of NiSix NWs on continuous Ni bulks using SiH4 vapor precursor at 400 °C. This growth is particularly marked in that NiSix NWs are formed in a self-organized manner without employing the nanocluster catalysts. We discuss this spontaneous growth of NiSix NWs within the frame of the nucleation kinetics in the low supersaturation limit in analogous with the earlier examples of the vapor-condensation at the low vapor pressures. [ABSTRACT FROM AUTHOR]

We measure absolute optical absorption cross-sections of one- (1D) and two-dimensional (2D) nanostructures using a focused laser beam while varying the numerical aperture (NA) of the focusing lens. We find the optical absorption deviates at higher NA. In the high NA regime, absorption by graphene decreases from 2.2% to below 1.8%; for Ge nanowires, it decreases from an expected value by a factor of 1.2. We explain this using the depolarization effect at the focal spot and conclude that these corrections allow for accurate quantitative measurements of optical and optoelectronic processes in 1D or 2D nanostructures. [ABSTRACT FROM AUTHOR]

We demonstrate fabrication of vertically aligned, intrananowire p-n diodes by large-area epitaxial growth of Si nanowires (NWs). The axially modulated doping profile of p-n junctions is achieved by in situ doping with alternating addition of dopants in the axial sequence during Au-assisted chemical vapor deposition. We provide direct evidence of the intra-NW p-n junctions using scanning local probes in both individual NWs and vertically aligned NWs at large areas. Our study suggests implication for integrated electronics and optoelectronics based on bottom-up Si NWs. [ABSTRACT FROM AUTHOR]

The authors present the demonstration of nanowire field-effect transistors incorporating group IV alloy nanowires, Si1-xGex. Single-crystalline Si1-xGex alloy nanowires were grown by a Au catalyst-assisted chemical vapor synthesis using SiH4 and GeH4 precursors, and the alloy composition was reproducibly controlled in the whole composition range by controlling the kinetics of catalytic decomposition of precursors. Complementary in situ doping of Si1-xGex nanowires was achieved by PH3 and B2H6 incorporation during the synthesis for n- and p-type field-effect transistors. The availability of both n- and p-type Si1-xGex nanowire circuit components suggests implications for group IV semiconductor nanowire electronics and optoelectronics. [ABSTRACT FROM AUTHOR]