Arrays of free-standing ZnSe nanowires of length 8-10 μm and diameter 60-150 nm were fabricated by Au-catalyzed vapor-liquid-solid growth. Electron microscopy showed that these were high quality single crystal nanowires. Photoluminescence (PL) measurements of the as-grown nanowires were characterized by weak near band edge emission and strong defect-related emission. The effect of post-growth annealing on the PL spectra under both Zn-rich and Se-rich conditions were studied. Annealing under a Zn-rich atmosphere was found to significantly enhance the near band edge emission and suppress deep-level emission, resulting in spectra dominated by the near band edge emission. On the other hand, annealing in a Se-rich atmosphere had the reverse effect, resulting in spectra dominated by deep level emission.
Photonic crystals consisting of semiconductor nanowire arrays grown using a metal catalyzed vapor-liquid-solid (VLS) method are excellent candidates for photonic elements and devices, such as micro-cavities, due to the high dielectric constant contrast and high aspect ratio. In addition, it is easy to control the crystal structure by patterning the metal catalysis, and the versatility of composition of nanowires (including II-VI, III-V and ternary III-V) makes the integration of optical components in diversified wavelength ranges possible. Here we use a Plane-Wave-Expansion (PWE) method and Finite Difference Time Domain (FDTD) technique toinvestigate the optical properties of nanowire based photonic crystals. It is found that arrays consisting of nanowires with radius at or below the edge of the effective single-wire confining range for a stand alone Fabry-Perot cavity can still form a high-Q value cavity with single mode operation. Our results will help to extend the concept of the-state-of-art 1-D distributed bragg reflector (DBR) and distributed feedback (DFB) lasers into 2-D ones with a working range from ultraviolet to near infrared.