We synthesized magnesium (Mg)-doped ZnO microspheres by laser ablation of a ZnO sintered target containing magnesium oxide (MgO) with the fundamental of a Nd:YAG laser at 1064 nm. The well-spherical ZnO microcrystals with diameters of 1-20 μm were collected on a substrate which was put near the ablation spot. X-ray diffraction and micro-Raman spectrum indicate that the ZnO microspheres have a crystalline structure. Room-temperature photoluminescence properties of the microsphere were investigated under third harmonic generation of a Nd:YAG laser excitation at 355 nm. An ultraviolet (UV) lasing in whispering gallery mode (WGM) and blue-shift of the UV WGM peaks were observed from the Mg-doped ZnO microsphere.
Various zinc oxide (ZnO) nanocrystals are expected as new building blocks for optoelectronic devices. Among them, we have studied about fabricating ZnO nanowires using nanoparticle-assisted pulsed laser deposition (NAPLD). Recently, we achieved to fabricate the periodically-aligned ZnO nanowires with a period of from 4 to 5 μm using interfering four-beams of nanosecond ultraviolet (UV) laser processing. ZnO nanowires with diameters of several dozen nanometers were grown on the ZnO buffer layer prepared by pulsed laser deposition at the low-chamber pressure of 3 Pa. Additionally, crystallization of ZnO nanoparticles collected on a sapphire substrate was achieved by UV-laser annealing. In this method, ZnO nanoparticles were collected at room temperature, then they were laser-annealed with a KrF excimer laser. The particle size increased by instantaneous melting and aggregation of ZnO nanoparticles because of the high absorption efficiency of ZnO in the UV spectral region. It was found that the optical property was improved by UV-laser annealing process. Additionally, their x-ray diffraction peaks of wurtzite ZnO crystals had narrower full width half maximum than those before laser annealing.
The dynamics of zinc oxide (ZnO) nanoparticles formed in Ar gas of 200 Torr by laser ablation are visualized by ultraviolet Rayleigh scattering imaging. The time-resolved imaging of the ZnO nanoparticles are presented for several conditions of single-pulse ablation and 10 Hz ablation at room temperature. Scattering light from the nanoparticles appeared at 1-2 ms after ablation, and the spatial distribution was a mushroom like swirling cloud. The cloud propagates forward about 2.6 m/s without lateral expansion. In addition, nanoparticle distribution at a substrate heating condition, which is growth condition of ZnO nanocrystals is investigated. The nanoparticles under heating condition formed almost the same spatial distribution as that of room temperature and their speed was increased to 3.2 m/s at 750 °C.
We succeeded in synthesizing antimony (Sb)-doped ZnO microspheres by ablating a ZnO sintered target containing 5 wt% of Sb with a Nd:YAG laser at a fluence of 25 J/cm2 in air. The well-spherical ZnO microcrystals with diameters of 1-20 μm were collected on a substrate which was put near the ablation spot. Most of the ZnO microspheres have a crystalline structure. In addition, Raman peak of the Sb-doped ZnO microspheres was shifted toward lower frequency side, indicating substitutional Sb3+ at Zn antisite. Room-temperature photoluminescence properties of the microsphere were investigated under 325 nm He-Cd laser or 355 nm Nd:YAG laser excitation. An ultraviolet (UV) emission and lasing in whispering gallery mode were observed from the photoexcited microsphere.
We have demonstrated that fabrication of the ZnO nanowire/GaN hetero-junction light emitting diode (LED) by
contacting the tip of the ZnO nanowires with the GaN film, and UV electroluminescence from the p-n junction. In this
study, we fabricated the heterojunction by directly-growth of the ZnO nanowires on the GaN film using nanoparticleassisted
pulsed laser deposition. Photoluminescence spectrum of the ZnO nanowires showed a weak near-band-edge
ultraviolet (UV) emission and a visible broad emission, which was related to transition by ZnO defect state. We applied a
selective laser irradiation to the p-n junction of the ZnO-based LED. The UV emission was strongly enhanced from the
laser-irradiated p-n junction.
Zinc oxide (ZnO) nano/microstructures have been attractive as the building blocks for the efficient opto-electronic
devices in the ultraviolet (UV) region. We have succeeded in growing the ZnO micro/nanosphere by a simple laser
ablation in the air, and therefore we have obtained UV lasing from the sphere under optical pumping. Recently, large size
of several 10 micrometer ZnO microspheres were grown using Nd:YAG laser without Q-switching, and ZnO
microsphere/p-GaN heterojunction were fabricated to obtain the electroluminescence (EL) from the microsphere by
electrical pumping. Room-temperature EL in near-UV region with peak wavelength of 400 nm is observed under
forward bias.
Effects of laser annealing on electrical and optical properties of Zinc oxide (ZnO) nanocrystals, which are expected as
building blocks for optoelectronic devices, have been investigated in this study. In the case of fabricating p-n junction in
single one-dimensional ZnO nanocrystal, phosphorus-ions implanted p-type ZnO nanocrystals were recrystallized and
recovered in the optical properties by nanosecond-laser annealing using a KrF excimer laser. Antimony-doped p-type ZnO
nanocrystals were synthesized by irradiating laminated structure which antimony thin film were deposited on ZnO
nanocrystals with the laser beam. Additionally, it is possible to control the growth rate of ZnO nanowires by using laser
annealing. Irradiating with pulsed laser a part of ZnO buffer layer deposited on the a-cut sapphire substrate, then ZnO
nanowires were grown on the ZnO buffer layer by the nanoparticle assisted pulsed laser deposition method. As a result,
the clear boundary of the laser annealed and non-laser annealed area was appeared. It was observed that ZnO nanowires
were grown densely at non-laser annealed area, on the other hand, sparse ones were grown at the laser-annealed region. In
this report, the possibility of laser annealing techniques to establish the stable and reliable fabrication process of ZnO
nanowires-based LD and LED are discussed on the basis of experimental results.
ZnO nanocrystals have received much attention as building blocks for nano/micro-devices due to their unique morphologies, electronic and optoelectronic properties. In order to apply the ZnO nanocrystals to the practical optoelectronic applications, control of the growth density, shape and position is required. We have achieved density-controlled ZnO nanowires and periodic ZnO nanostructures using laser interference patterning. Various shapes of ZnO nanostructure, such as microcylinder and aligned nanowall, were grown using interference patterned film and substrate. In addition, optically pumped ultraviolet lasing from a piece of the ZnO nanocrystal was achieved.
We have proposed the ZnO film annealing method using CO2 laser. We fabricated the layered structure to enhance the
annealing effect. The sample structure was SiO2/ZnO/Quartz substrate. The ZnO film was deposited on quartz by a
pulsed laser deposition and the SiO2 film was deposited on ZnO film by physical vapor deposition. We used
photoluminescence measurement to investigate the optical property of ZnO film. We found that the optical property was
improved in two steps. The first step was surface passivation effect of SiO2 coating and the second one was the annealing
effect of CO2 laser. We analyzed the fabricated film for surface state by XPS and for crystallinity by TEM measurements.
The change of ZnO surface state was observed when the SiO2 film was deposited on the ZnO film. The change of
crystallinity of ZnO was observed after CO2 laser annealing. The crystallinity of ZnO before laser annealing seemed to
be polycrystal, while the crystallinity of ZnO after laser annealing seemed to be single crystal.
Zinc oxide (ZnO) has a wide band-gap energy of 3.37 eV and a large exciton binding energy of 60 meV which is considerably larger than the thermal energy at room temperature (26 meV), and therefore, efficient exciton emission in ultraviolet (UV) region can be expected. Especially, ZnO micro/nanocrystals are quite attractive as building blocks for efficient UV opto-electronic devices. We have been investigating micro-cavity UV lasing from variously-shaped ZnO micro/nanocrystals, and micro-cavity lasing from ZnO nanowire and nanosheet have been confirmed, so far. Recently, we could fabricate ZnO micro/nanosphere crystals by a simple laser ablation method of ZnO sintered target in the air. In this study, we report UV micro-cavity lasing from an optically-pumped single ZnO micro/nanosphere crystal, for the first time. The spherical-micro-cavity lasing characteristics were investigated and discussed by comparisons with theoretical considerations in terms of quality factor and mode spacing of its lasing spectra with modal structures. From those considerations, it was found that the lasing mechanisms within a ZnO sphere crystal was attributed to whispering-gallery- mode (WGM) cavity lasing, and a ZnO sphere crystal had a good light confinement property due to the internal total reflections. Since the fabrication method is very simple and productive without any time-consuming crystal-growth process, ZnO micro/nanosphere crystals can be promising building blocks for UV opto-electronic devices such as a UV laser diode. In addition, since a ZnO micro/nanosphere can operate as an active WGM refractometric sensor for small molecules in UV region, high sensitivity enhanced by high quality factor, refractive index, and wavelength dispersion can be expected.
Zinc oxide (ZnO) has attracted considerable attension due to its wide applications in particular ultra violet light emitting diode (UV-LED). In addition, the one-dimensional ZnO crystals are quite attractive as building blocks for light emitting devices like laser and LED, because of their high crystallinity and light confinement properties. However, a method for the realization of the stable p-type ZnO has not been well established. In our study, we have investigated the effect of the nanosecond laser irradiation to the ZnO nanorods as an ultrafast melting and recrystallizing process for realization of the p-type ZnO. Fabrication of the p-n homo junction along ZnO nanorods has been demonstrated using phosphorus ion implantation and ns-laser annealing by a KrF excimer laser. Rectifying I-V characteristics attributed to p-n junction were observed from the measurement of electrical properties. In addition, the penetration depth of laser annealed layer was measured by observing cathode luminescence images. Then, it was turned out that high repetition rate laser annealing can anneal ZnO nanorods over the optical-absorption length. In this report, optical, structural, and electrical characteristics of the phosphorus ion-implanted ZnO nanorods annealed by the KrF excimer laser are discussed.
Zinc oxide (ZnO) nano-crystal is great interest for optoelectronic applications in particular ultraviolet (UV) region such as UV-LEDs, UV-lasers, etc. For the practical optoelectronic applications based on the ZnO nanocrystals, control of nanowire growth direction, shape, density, and position are essentially required. In our study, we introduced a ZnO buffer layer and interference laser irradiation to control the growth position of ZnO nanocrystals. In this presentation, structural and morphological characteristics of periodic ZnO nano-crystals synthesized by the nanoparticle-assisted pulsed laser deposition will be discussed.
We have succeeded in growing various ZnO nanocrystals, such as nanowires, nanorods, and nanowalls, by a
nanoparticle-assisted pulsed-laser deposition (NAPLD). In this study, low-density ZnO nanowires were synthesized by
introduction of a ZnO buffer layer. Low-density hexagonal cone-shape ZnO cores are formed on the buffer layer, and
vertically-aligned ZnO nanowires are grown on the cores. The density of the nanowires was clearly decreased with
increasing the thickness of the Buffer layer. The buffer layer can be used as one of the effective additives to control the
growth density of the ZnO nano-crystals synthesized by NAPLD.
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