Nanowire Optoelectronics

Semiconductor nanowires have been used in a variety of passive and active
optoelectronic devices including waveguides, photodetectors, solar cells,
light-emitting diodes (LEDs), lasers, sensors, and optical antennas. We review
the optical properties of these nanowires in terms of absorption, guiding, and
radiation of light, which may be termed light management. Analysis of the
interaction of light with long cylindrical/hexagonal structures with
subwavelength diameters identifies radial resonant modes, such as Leaky Mode
Resonances, or Whispering Gallery modes. The two-dimensional treatment should
incorporate axial variations in “volumetric modes,”which have so far been
presented in terms of Fabry–Perot (FP), and helical resonance modes. We report
on finite-difference timedomain (FDTD) simulations with the aim of identifying
the dependence of these modes on geometry (length, width), tapering, shape
(cylindrical, hexagonal), core–shell versus core-only, and dielectric cores with
semiconductor shells. This demonstrates how nanowires (NWs) form excellent
optical cavities without the need for top and bottommirrors. However, optically
equivalent structures such as hexagonal and cylindrical wires can have very
different optoelectronic properties meaning that light management alone does not
sufficiently describe the observed enhancement in upward (absorption) and
downward transitions (emission) of light inNWs; rather, the electronic
transition rates should be considered. We discuss this “rate management” scheme
showing its strong dimensional dependence, making a case for photonic integrated
circuits (PICs) that can take advantage of the confluence of the desirable
optical and electronic properties of these nanostructures.