Norihiro Tetsuyama

Ultraviolet electroluminescence from hetero p-n junction between a single ZnO microsphere and p-GaN thin film.

We report ultraviolet electroluminescence from a hetero p-n junction between a single ZnO microsphere and p-GaN thin film. ZnO microspheres, which have high crystalline quality, have been synthesized by ablating a ZnO sintered target. It was found that synthesized ZnO microspheres had a high-optical property and exhibit the laser action in the whispering gallery mode under pulsed optical pumping. A hetero p-n junction was formed between the single ZnO microsphere/ p-GaN thin film, and a good rectifying property with a turn-on voltage of approximately 6 V was observed in I-V characteristic across the junction. Ultraviolet and visible electroluminescence were observed under forward bias.

Applications of nanosecond laser annealing to fabricating p-n homo junction on ZnO nanorods

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.

Emission characteristics of electrically- and optically-pumped single ZnO micro-spherical crystal

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.

Electroluminescence from ZnO nanowire-based heterojunction LED

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.

Control of optical and electrical properties of ZnO nanocrystals by nanosecond-laser annealing

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.

Fabrication of UV-LED using ZnO nanowires directly grown on p-GaN film by NAPLD

We report the direct of ZnO nanowires on a p-GaN film by Nano-particle Assisted Pulsed Laser Deposition (NAPLD) and the ultra-violet electroluminescence characteristic from the fabricated p-n heterojunction LED.

Effect of High Repetition Pulsed Laser Annealing on Optical Properties of Phosphorus Ion-Implanted ZnO Nanorods

We report on the effect of high repetition pulsed laser annealing with a KrF excimer laser on the optical properties of phosphorus ion-implanted ZnO nanorods. The recovery levels of phosphorus ion-implanted ZnO nanorods have been measured by photoluminescence spectra and cathode luminescence (CL) images. After ion implantation on the surface of ZnO nanorods, CL was disappeared over 400 nm below the surface due to the damage caused by ion implantation. When the annealing was performed at a low repetition, CL was recovered only shallow area below the surface. The depth of the annealed area was increased with the repetition rate of the annealing laser. By optimizing the annealing conditions such as the repetition rate, the irradiation fluence and so on, we have succeeded to anneal the whole damaged area over 400 nm in depth and to observe CL. Thus, the effectiveness of high repetition pulsed laser annealing on phosphorus ion-implanted ZnO nanorods was demonstrated.