A considerable amount of research has been done regarding one dimensional semiconductor nanowires. In particular, group-IV semiconductor nanowires such as silicon and germanium nanowires (SiNWs and GeNWs) have attracted attention as NW-based devices are of interest for their compatibility with present Si complementary metal-oxide semiconductors (CMOS) integrated circuit technology. Here I will report the growth and impurity doping of group-IV semiconductor NWs. Laser ablation and chemical vapor deposition methods using vapor-liquid-solid growth mechanism will be discussed. Impurity doping is one of the important techniques to functionalize NWs. The crucial point is how the states of impurity atoms can be clarified. I will introduce results characterized by Raman scattering and electron spin resonance, showing that B and P atoms were doped and electrically activated in SiNWs and GeNWs. Finally, data for core-shell NWs using Si and Ge will be introduced, which are expected to be of use in next generation high-speed transistor channels.

  One crucial challenge for semiconductor nanowires has been the development of a complementary metal–oxide–semiconductor (CMOS)-compatible synthesis approach which produces semiconductor heterostructure nanowire with excellent optical and electrical properties. This remains challenging mostly because gold (Au), which is widely used as a catalyst particle when nanowires are synthesized with the bottom-up vapor-liquid-solid (VLS) approach¹, is not permitted in the mainstream CMOS process as Au is highly detrimental to the performance of minority carrier electronic devices^{2, 3}. Here we describe the growth, structural and optical properties of InP, InAs and InP/InAs heterostructure nanowires by developing an Au-free indium-particle-catalyzed (or self-catalyzed) VLS approach. The nanowire exhibits excellent optical property, enabling lasing operation with tunable lasing wavelength range in full telecom band at room temperature. We also present a novel approach to form the site-defined InP/InAs nanowires by combining bottom-up self-assembly with top-down micro-photolithography technique. We have also revealed a distinct growth phenomenon of self-catalyzed VLS approach that the catalyst particle size (thus, the nanowire diameter) can be tailored by modulating V/III flow ratio during the growth process.

  We report the analysis of twinning-superlattice formation in group III-V semiconductor nanowires (NWs) by considering two-dimensional nucleation using surface and twinning energies obtained by performing electronic structure calculations within density functional theory. The calculations for GaP, GaAs, InP, and InAs demonstrate that surface energies strongly depend on the growth conditions such as temperature and pressure during the epitaxial growth. Furthermore, the calculated twinning energies are found to be much smaller than previously estimated values by the dissociation width of edge dislocations, which lead to smaller segment length of twinning-superlattice. The nonlinear relationship between segment length and nanowire diameter depending on constituent elements mainly originates from the difference in twinning energies. These results imply that twinning formation as well as surface stability are crucial for the formation of twin plane superlattices in group III-V semiconductor NWs.

  From around the beginning of this century, semiconductor nanowires have been paid attention as a promising building block for nanotechnology. They have realized ultra-small and functional electronic and photonic devices, utilizing their self-assembled nanoscale 1-dimensional structure applicable to charge carriers and optical waveguides. On the other hand, thin-film GaAs-related compound semiconductor heterostructures had realized high-speed and high-efficiency devices, e. g., lasers, sensors, transistors, electro-optical modulators, and solar cells. Over the past decades, the function of GaAs was extended by the introduction of small amount of nitrogen and bismuth. Diluting those materials provides the greater tunability of band gap and strain status, or is expected to suppress non-radiative recombination. Selective oxidation for Al-rich AlGaAs is a vital technique for vertical surface emitting lasers, enabling the optical and electrical confinement, heat transfer, and mechanical robustness. The author tried to introduce the above thin-film technology to extend the functions of compound semiconductor nanowires.

  Single crystalline metal oxide nanowires have demonstrated a great promise for IoT sensors, biomedical and environment-analytical devices because of their thermal/chemical robustness in air and water conditions. This report introduces a rational concept for designing the single crystalline metal oxide nanowires. The anisotropic nanowire growth can be achieved by rigorously controlling a material supply flux or a precursor concentration within an appropriate range, so-called “flux/concentration window”. The flux/concentration window is determined by the competitive nucleation events at different crystal growth interfaces. Recent our study shows the critical importance of the flux/concentration window to control not only the nanowire structure, but also their composition, crystal phase and functional properties.