Controlled growth of ZnO nanowires and their optical properties (original) (raw)
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ACS Applied Materials & Interfaces, 2012
ZnO thin films were deposited on glass substrate using a sol-gel method. The structural and optical properties at different annealing temperatures were studied using X-ray diffraction (XRD), ultra-violet-visible spectroscopy and Raman spectroscopy. X-ray diffraction results show that the c-axis orientation became stronger as the annealing temperature increased from 300 to 500 º C. the optical band gap energy was calculated from the optical absorption using UV-Vis spectrophotometer. The optical band gap of ZnO thin films decreases from 3.378 eV to 3.338 eV as the annealing temperature increases from 300 to 500 ºC, the experimental data are in agreement with the calculated results by specific models of refractive index.
Fundamentals of zinc oxide as a semiconductor
Reports on Progress in Physics, 2009
In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.
Journal of Nanoscience and Nanotechnology, 2012
Using a hot-walled pulsed laser deposition (HW-PLD), nanowires (NWs) comprising 3 weight% Ga-doped ZnO (3GZO) have been successfully grown on a sapphire substrate. The structural and optical properties of 3GZO nanostructures have also been systematically investigated with respect to the target-substrate (T-S) distance and the growth temperature. The morphology transformations of nanostructures such as nano-horns, NWs, and clusters are strongly affected by growth temperatures due to different thermal energy. Also, the morphologies of nanostructures-including length, diameter, and density-are strongly affected by the T-S distance, illustrating a close correlation between the growth kinetics and the position in the plume formed by the particles from the GZO target. Also, the exciton that is bound to the neutral donor (D 0 X) peak of the 3GZO nanostructures is found at the low temperature PL spectra, indicating successful Ga-doping into ZnO NWs.
We report on the growth of ZnO nanostructures on n-type silicon substrate using pulsed laser deposition technique at substrate temperature ranging from room temperature to 600 ∘ C for one hour. We observe both rod-and wire-like structures with different dimensions at room temperature, 150 ∘ C, and 450 ∘ C substrate temperatures and only wire-like structures at 300 ∘ C and 600 ∘ C. These combinations of different shapes have been attributed to the initial growth of nanostructures (nucleation sites) on the surface obtained during the deposition for 20 minutes. The narrowing in the full-width-half-maximum of the peak corresponding to (002) plane of XRD is looked upon as another possible explanation. The blue shift of the peak at 396 nm observed in the photoluminescence is due to the quantum confinement. The intensity of 2 (high) mode at 437 cm −1 increases indicating improvement in crystallinity with the substrate temperature.
ZnO Nanowire Heterostructures: Intriguing Photophysics and Emerging Applications
2013
Over the last decades, semiconductor nanowires have been extensively studied for their applications in several disciplines. Many of these applications require heterostructures, which can be defined as the combination of two or more materials within the same nanowire structure. Recent research on the ZnO nanowires (NWs) heterostructures shows the possibility to overcome the existing limitation of the bare ZnO NWs based optoelectronic devices. Prospects for the commercialization of ZnO NWs based devices using the heterostructure approach are intensively pursued at present. This review article summarizes the current status of research worldwide and the findings from our group on various aspects of the ZnO NW heterostructures: fabrication methodologies, structural characterization, photophysical properties and related emerging applications. The fascinating properties of the ZnO NW heterostructures and its applications in different devices, mainly UV photodetectors, light-emitting-diodes, dye sensitized or quantum dots sensitized solar cells and photoelectrochemical cells are discussed. Focus of the article is on the impact of heterostructure approach on the selective properties and performance of the ZnO NWs based devices. The improvements in the key parameters of these devices are also discussed to highlight the effectiveness of the heterostructure approach and a future outlook of the field is presented at the end.
Self-seeded growth and ultraviolet photoresponse properties of ZnO nanowire arrays
Applied Physics Letters, 2007
The authors report on the self-seeded growth of ZnO nanowire ͑NW͒ arrays on glass substrates by a simple solvothermal method using two different sol concentrations for the seed layer formation. The formations of hexagonal-shaped NWs with diameter of 20-60 nm on the seed layer for 0.1M sol and mostly of trapezoidal-shaped NWs with base width of 135 nm on the seed layer for 0.03M sol have been explained considering the longitudinal and transversal growths of ZnO NWs. The photocurrent behavior of ZnO NW arrays in air as well as in vacuum is analyzed in terms of adsorbed oxygen and water molecules.
Optical Applications of ZnO Nanowires
IEEE Journal of Selected Topics in Quantum Electronics, 2000
This paper discusses different aspects of optical applications of ZnO nanowires NWs. After a description of the relevant synthesis and fabrication techniques, light-emitting diodes based on ZnO NW and NW arrays are introduced and different experimental realizations from the literature are discussed. The working principle of ZnO UV photodetectors is presented, and improvements and limitations of ZnO-NW-based dye-sensitized solar cells are discussed. Different aspects of ZnO-NW waveguides and their potential application for biological sensing are described. Finally, the current status of ZnO-NW-based UV lasers is presented.