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.

Multilayer Ti∕Au contacts were fabricated on individual, unintentionally doped zinc selenide nanowires with 80nm nominal diameter. Four-terminal contact structures were used to independently measure current-voltage characteristics of contacts and nanowires. Specific contact resistivity of Ti∕Au contacts is 0.024Ωcm2 and intrinsic resistivity of the nanowires is approximately 1Ωcm. The authors have also measured the spectral photocurrent responsivity of a ZnSe nanowire with 2.0V bias across Ti∕Au electrodes, which exhibits a turnon for wavelengths shorter than 470nm and reaches 22A∕W for optical excitation at 400nm.

We have observed ferromagnetism in dilute (∼1–4at.%) Mn-doped crystalline ZnO nanowires at temperatures up to 400K. Arrays of freestanding single crystal ZnO:Mn nanowires were fabricated by Au-catalyzed vapor-liquid-solid growth. Structure and compositional analyses revealed that Mn was incorporated into the ZnO lattice. From the observed saturation magnetization, the magnetic moment per Mn atom is estimated to be between 0.3μB and 1.2μB. Photoluminescence measurements show a strong suppression of defect related midgap emission, indicative of an interplay between Mn doping and native point defects.

In this work, the origin of the deep level, defect related photoluminescence emission band in ZnSe is investigated. Using the dependence of the peak energy on excitation intensity, it was shown to originate from donor-acceptor pair recombination. The binding energy of the donor-acceptor pair was estimated to be 18±0.5meV and the shallow impurity Bohr radius was estimated to be 9.1±0.2nm. Using a postgrowth annealing treatment in a Zn atmosphere, the two species involved in the donor-acceptor pair recombination process were attributed to Zn vacancies and Zn interstitials.

In this paper, we study tunable holographic lithography using an electrically addressable spatial light modulator as a programmable phase mask. We control the phases of interfering beams diffracted from the phase pattern displayed in the spatial light modulator. We present a calculation method for the assignment of phases in the laser beams and validate the phases of the interfering beams in phase-sensitive, dual-lattice, and two-dimensional patterns formed by a rotationally non-symmetrical configuration. A good agreement has been observed between fabricated holographic structures and simulated interference patterns. The presented method can potentially help design a gradient phase mask for the fabrication of graded photonic crystals or metamaterials.