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SiO2 nanoporous films has been attracting attention as low-k dielectric constant insulating films. We have succeeded in SiO2 nanoparticles with a particle size of a few nm and depositing a nanoporous film by pulsed laser deposition with controlling the ambient gas pressure. However, the details of the formation process of SiO2 nanoparticles have not been clarified. In this study, we visualized the time-resolved nanoparticle distribution in the gas phase by laser imaging technique to clarify the nanoparticle formation process and to be helpful for optimizing the growth condition of the low-k nanoporous film.

The formation of a twisted Au microstructure was demonstrated by irradiating the Au thin film with a focused optical vortex laser pulse. The theoretically calculated torque generated by optical radiation force of optical vortex was confirmed to be consistent with the twist direction of the experimental results. The microstructures formed by changing the focal position were experimentally investigated. Through simulations, it was shown that the spherical wave of the focused beam may affect the distribution of the optical radiation force at the defocus positions.

The crystallization of a-Si leads to alterations in the morphology of Si film such as surface color and surface roughness as a result of excimer laser annealing (ELA). These surface changes correlate with the characteristics of polysilicon films. The quality of crystallized poly Si has been evaluated by Non-destructive optical inspection methods. This study aims to use deep learning to estimate the quantitative relationship between the microscope images of a low-temperature polycrystalline silicon (LTPS) film and the mobility of an LTPS thin film transistor (TFT). This method would make it possible to measure the mobility from the images captured after annealing and improve the crystallization by in situ feedback. An a-Si substrate with a film thickness of 100 nm was polycrystallized by employing a KrF (wavelength of 248 nm) excimer laser, after which an optical microscope image of the substrate was captured. By changing the laser fluence and the number of shots (44 conditions N=10), LTPS films of various surface morphology were fabricated. We fabricated 440 transistors using these LTPS channels (channel size L = 20 μm, W = 30 μm) and measured their mobilities. Then, we performed deep learning with these sets of annealed optical microscope images and the corresponding mobilities. The mobility was estimated with an accuracy of ±12.8 cm2 V-1 s-1. Further improvement of the prediction accuracy (

Low-temperature poly-Si (LTPS) thin films formed by excimer laser annealing (ELA) are used as the channel material for thin film transistors (TFTs), which have an application as switching devices in flat panel displays. It is well known that one of the major problems in TFT manufacturing is the prominent ridges that form on LTPS thin films after ELA due to volume expansion by crystallization, which in turn induces gate leakage current in the TFTs. In this presentation, we report on the use of additional laser irradiation to reduce the height of the ridges and resulting changes in the electrical properties of LTPS-TFTs.

We have demonstrated the fabrication of semiconductor microspherical crystals such as ZnO and Si microspheres by a simple laser ablation technique. In addition, doped and alloyed microspheres have achieved by this technique. The fabrication mechanism of the spherical crystals is based on instantaneous heating of target material, formation of spherical shape by surface tension of liquid-state material, and rapid freezing with keeping the spherical shape. In this study, the technique is expanded to other various materials, and microspheres consisting of multicomponent semiconductor such as Sr3Sn2O7 was successfully fabricated. This technique is a candidate for fabrication of functional microspherical crystals.

Ultra-large scale integrated circuits (ULSIs) have been continually scaled down according to Moore’s law. This can improve their power consumption and operation frequency but not the RC delay of their interconnections; to this end, super low dielectric constant films are required. We propose a novel method to fabricate porous SiO2 films with a super low dielectric constant by F2 laser deposition. In this method, a quartz target is evaporated by F2 laser ablation in vacuum-chamber-controlled Ar partial pressure. The evaporated SiO2 molecules are agglomerated in the vacuum, and the size of the SiO2 nanoparticles are controlled by the Ar partial pressure. Porous SiO2 films are formed on a Si-receiving substrate, which is placed in front of the quartz target. The pulse duration of the F2 laser was approximately 20 ns, and the repetition rate of laser shots was 100 Hz. The base pressure of the vacuum chamber was 5 × 10−3 Pa. Then, Ar gas was introduced into the vacuum chamber through a mass flow controller to control the Ar partial pressure. The dominant size of the SiO2 nanoparticles decreased from 1.5–2.0 nm to 1.0–1.5 nm with the Ar partial pressure decreasing from 20 Pa to 4.5 Pa. In addition, the relative dielectric constant k of the porous SiO2 film formed at an Ar partial pressure of 4.5 Pa was 2.8, which is lower than that of thermal SiO2 (k = 4.0). In addition, the leakage current of the nanoporous SiO2 film was almost equal to that of the thermal SiO2 film. From these results, we conclude that nanoporous SiO2 films with a super low dielectric constant can be formed by F2 laser deposition.

We propose low-temperature and high-concentration doping of 4H-silicon carbide (4H-SiC)(0001) by KrF excimer laser irradiation of source films on a 4H-SiC substrate, in which a dopant atom is included. In n-type doping, a SiN x film with a thickness of 100 nm was deposited on an n-type 4H-SiC(0001) substrate by chemical vapor deposition. A gas supply nozzle for ambient environment control was installed to prevent oxidation of the SiC surface. High-concentration nitrogen doping (~1 × 10 21 /cm 3 at the surface) was achieved by laser ablation of the SiN x film. Al/Ti electrodes were formed on the doped area at a room temperature, and a contact resistance of 2.2 × 10 -5 Ω･cm 2 was obtained, which is sufficiently small for the backside contact resistance of Schottky barrier diodes. In p-type doping, an Al film with a thickness of 240 nm was deposited on a 4H-SiC substrate by sputtering deposition. After laser irradiation of the Al film in ambient Ar, high-concentration Al doping (~1 × 10 21 /cm 3 at the surface) was achieved. Al/Ti electrodes were formed on the doped area at a low temperature of 600 °C, and a contact resistance 1.9 × 10 -4 Ω･cm 2 was obtained. We conclude that low-temperature and high-concentration doping of 4H-SiC for low contact resistance can be achieved by laser ablation of the source films on the 4H-SiC substrate.

The electrical properties of poly-Si thin films doped using KrF excimer laser irradiation with a phosphoric-acid coating were investigated. After laser doping, the mobility, carrier concentration, activation ratio, and contact resistivity of the poly-Si were found to be 61 cm2 /Vs, 1.5×1018 cm-3 , 18.1 %, and 8.5 × 10−5 Ω⋅cm2 , respectively. Additionally, the operation of a bottom gate transistor fabricated using laser doping was realized and is described herein.

We have succeeded in synthesizing zinc oxide (ZnO) microspherical crystals and Silicon microspheres by a simple laser ablation technique in air, and demonstrated whispering-gallery-mode (WGM) lasing from optically-pumped ZnO microsphere. ZnO/MgO alloy microspheres were also successfully fabricated, and blue-shift of WGM lasing wavelength was achieved. Recently, size-controlled and on-demand fabrication of semiconductor microspheres by introducing of an optical vortex beam.

ZnO nano/microstructures have attracted much attention as building blocks for optoelectronic devices because of their high crystalline quality and unique structures. We have succeeded in synthesizing ZnO microspherical crystals by a simple atmospheric laser ablation method, and demonstrated ultraviolet whispering-gallery-mode lasing from the spheres. In the microsphere synthesis process, molten droplets formed into spherical shapes by surface tension, and crystalized during ejection from the ablation spot. In this study, we observed the generation of ZnO microspheres by high-speed camera. Now we are trying to control and manipulate the microspheres using a vortex beam.

We propose an innovative method for aluminum doping of 4H-SiC with passivation films, induced by XeF excimer laser irradiation in AlCl3 aqueous solution (28.6 wt%). A 100-nm thick Si passivation film was deposited on an n-type 4H-SiC substrate by physical vapor deposition. Using a laser beam (200 μm × 170 μm) with an irradiation fluence of 0.5–5.0 J/cm 2 , 1–300 shots were administered. After laser irradiation of 1.0 J/cm 2 and 300 shots, an Al-Si-O compound film was formed on the SiC surface. The compound film was removed by chemical wet etching and plasma treatment. After the removal of the compound film, no irradiation damage was observed on the SiC surface. From the results of secondary ion mass spectrometry measurements, high concentration aluminum doping (about 1 × 10 20 /cm 3 at the surface) was confirmed. The I-V characteristics of the junction between the n-type substrate and the irradiation area indicated clear rectification with a large on/off ratio of 9 decades in the range of ±10 V. When forward biased, electroluminescence phenomenon with a peak at 387 nm, corresponding to the electroluminescence of SiC’s band gap, was confirmed. These results prove the achievement of Al doping of n-type SiC to p-type using laser irradiation without any damage to the SiC surface.

We have proposed a novel method of low-temperature nitrogen doping into 4H-SiC(0001) induced by KrF excimer laser irradiation to a SiNx film. The SiNx film with a thickness of 100 nm was deposited on an n-type 4H-SiC(0001) substrate by chemical vapor deposition. Laser beam size on the sample surface was 300 μm×300 μm. Irradiation fluence was 1.0 J/cm2-4.0 J/cm2, and the number of shots was from 1 shot to 30 shots. Laser irradiation was performed in a vacuum chamber to avoid oxidation of the SiC surface. High concentration nitrogen doping (~1×1021 /cm3 at the surface) and very low contact resistance with ohmic I-V characteristics can be achieved by laser ablation of the SiNx film. In the case of laser irradiation at the fluence of 2.0 J/cm2, the SiNx film was almost ablated without laser ablation of the SiC substrate. Then, excellent ohmic contact characteristics was obtained at the irradiation number of 5 shots, and it was hardly deteriorated up to 30 shots. In the case of irradiation fluence above 3.0 J/cm2, ablation of the SiC substrates was induced and ohmic contact characteristics were deteriorated with increasing the number of shots. From these results, we conclude that excellent ohmic contact characteristics without irradiation damage to SiC substrates can be obtained in a stable.

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.

Observation of graphene growing process on SiC(0001) step and terrace structure formed by direct laser patterning is proposed. We have proposed a novel method of direct growth of patterned graphene on SiC(0001) surfaces using KrF excimer-laser irradiation. KrF excimer-laser with a wavelength of 248 nm and a duration of 55 ns was used to graphene forming in this study. Laser irradiation was achieved with various laser fluenece. Grain size and number of layers of the graphene was varied by laser irradiation condition. Through conductive atomic force microscopy, it was observed that graphene grain expanded from (112 _ n) faced step area to (0001) faced terrace area in initial graphene growth process. From the result of the Raman spectroscopy, transmission electron microscopy and Conductive AFM, we summarized graphene growth process on SiC(0001) surfaces.

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.

A novel method of direct growth of patterned graphene on SiC(0001) surfaces using KrF excimer-laser irradiation is proposed. It relies on the local sublimation of Si atoms within the irradiated area to induce graphene growth through a rearrangement of surplus carbon. A laser with a wavelength of 248 nm was pulsed with a duration of 55 ns and a repetition rate of 100 Hz that was used to graphene forming. Following laser irradiation of 1.2 J/cm2 (5000 shots) under an Ar atmosphere (500 Pa), characteristic graphene peaks were observed in the Raman spectra of the irradiated area, thereby confirming the formation of graphene. The ratio between the graphene bands in the Raman spectra was used to estimate the grain size at 61.3 nm. Through high-resolution transmission electron microscopy, it was confirmed that two layers of graphene were indeed formed in the laser irradiated region. Using this knowledge, we also demonstrate that line-and-space (LandS) graphene patterns with a pitch of 8 μm can be directly formed using our method.

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.

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.

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.

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 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.