In order to realize the full potential of nanowires for optical applications, it is essential to synthesize nanowires that can emit predominantly via band to band or band edge (BE) transitions. However, many compound semiconductor nanowires, irrespective of the method of their growth, contain a high density of native defects; these result in competing deep defect (DD) related emission, limiting their utility for optoelectronic device applications. The concentration of these native defect states depends on the gas phase stoichiometry. In this work, we report on the influence of gas phase stoichiometry on the structural and optical properties of single crystal zinc selenide (ZnSe) nanowires. We find that nanowires grown under stoichiometric conditions contain such defect states with associated weak BE emission and strong DD emission. However, nanowires grown under Zn-rich conditions were characterized by photoluminescence spectra dominated by strong BE emission while those grown under Se-rich conditions showed strong DD related emission. Hence, it is necessary to develop a strategy for enhancing the BE emission while simultaneously quenching the DD emission. We demonstrate a technique of postgrowth treatment that can effectively perform this function, and using this strategy the ratio of the BE/DD emission can be increased by a factor of several thousands, at least an order of magnitude higher than previously reported values. This reveals BE dominated photoluminescence in these nanowires and makes these nanowires suitable for developing future optoelectronic devices.

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The synthesis of ZnSe nanowires is a rapidly expanding research field with numerous applications. Key to realizing the potential of such nanowires is an ability to prepare structurally uniform defect-free material. Microstructure studies on as-grown nanostructures reveal that the structure of these nanowires are highly sensitive to the growth temperature, with higher temperature growth (750°C) resulting mostly in nanoribbons having different morphologies. Planar defects (mainly stacking faults and twins) are found to extend throughout the nanoribbons. At lower growth temperatures (650°C) structurally uniform nanowires are typically found. Photoluminescence (PL) measurements on crystalline nanowires show that the spectrum comprises two characteristic peaks corresponding to strong near band edge emission, and a weaker emission associated with defect states. However, the PL spectra of ZnSe nanoribbons which contain a high density of structural defects are dominated by defect related emission.

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Arrays of free-standing ZnSe nanowires with the length of 8–10μm and diameters of 80–150nm were fabricated by Au-catalyzed vapor-liquid-solid growth. Current-voltage characteristics of the arrays over the temperature interval of 90–400K showed a superlinear character. The differential conductance varied between two saturating regimes at low and high biases, respectively. This behavior was explained using a model of nonuniform wires with concentration fluctuations along them. The nanowire photoconductivity had a spectral edge corresponding to the ZnSe band gap and a strong frequency dispersion, presumably due to carrier capture by deep centers.

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