Tailoring Light-Matter Interactions in Semiconductor Nanowires with Nanocavity Plasmons

Controlling the optical properties of semiconductors with an engineered surface plasmon nanocavity is of great importance for understanding the underlying physics and designing new nanoscale photonic devices including highly efficient photovoltaics. In this talk we will demonstrate highly enhanced absorption and also emission from single CdS-SiO₂-Ag core-shell plasmonic nanowires, properties of which are different from simple photonic CdS nanowires. We will demonstrate that by fabricating a complete nanoplasmonic cavity, drastically enhanced absorption in comparison to metal nanoparticles attached to the nanowires is obtained due to the optical antenna effect, which can be tuned completely by controlling the nanowire size. Likewise, by tuning the plasmonic cavity size to match the whispering gallery mode resonances, an almost complete transition from thermalized excitonic to hot-excitonic emission can be achieved, which reflects exceptionally high radiative rate enhancement. Time-resolved measurements for the plasmonic nanowires showed the excited-state lifetime shortening by a factor of >1000, resulting in sub-picosecond lifetimes. Numerical calculations also confirms that the electromagnetic field enhancement by the whispering gallery plasmon nanocavity is as high as 5000 in these structures. In addition, we also demonstrate bright light emission from Si nanowires with large diameters (~100 nm) coupled to a plasmonic nanocavity due to hot carrier recombination with a quantum efficiency of ~1%. This represents many orders of magnitude radiative rate enhancement over their photonic counterparts, which can be useful for fabricating Si-based light emitting devices. Another example is the ~300X enhancement in second-harmonic generation signals from metal-coated semiconductor nanowires due to optimum mode confinement leading to very large optical fields. These observations indicate that the intrinsic optical properties of semiconductors can be engineered- by their interaction with nanocavity plasmons and is important for understanding and designing nanoscale optoelectronic devices with tailored responses.