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Laser-assisted doping of intrinsic silicon carbide (SiC) films deposited on Si (100) substrates by pulsed laser deposition (PLD) method and its influence on simultaneous annealing of the thin film is studied. PLD grown intrinsic SiC films are transformed to p-type SiC and n-type SiC, using laser-assisted doping in aqueous aluminum chloride and phosphoric solutions, respectively. Simultaneous doping and annealing of the SiC film are observed during laser-assisted doping. By precisely positioning the selectively doped region, lateral p–n diodes are formed on the SiC films without using any mask. Electric characteristics confirmed the formation of a lateral p–n diode structure. Numerical analysis of temperature distribution along the depth of the SiC films explains the mechanism of simultaneous doping and annealing during the laser treatment.

Currently, low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs), which are characterized by high mobility of electrons, are fabricated by excimer laser annealing. High mobility in low-temperature polycrystalline silicon is achieved by controlling the grain size to approximately 300 nm. However, with future potential growth of active-matrix organic light-emitting diodes in terms of their increasing use as backlight in active matrix micro-LEDs, even higher mobility is required. One of the methods to improve mobility is to produce grains of sizes above 300 nm. However, as far as we know, there are no reports of investigating the dependence between the device characteristics and the grain size of above 300 nm. In this study, we examine the possibility of controlling the grain size above approximately 350 nm by laser annealing with an intensity distribution and investigate the grain size dependence of the TFT characteristics. We show that the grain size can be controlled approximately in the range of 1–2.5 $\mu \text{m}$ , and mobility of 248±28 cm2 V−1s−1 is achieved at a grain size of 2.5 $\mu \text{m}$ . Furthermore, we compare the device characteristics of the step-and-repeat and scan annealing and verify that the device characteristics do not deteriorate even during scan annealing. The study confirms that it is technically possible to produce LTPS with grain sizes controlled in the range of 1–2.5 $\mu \text{m}$ for customizing device characteristics.

A laser-induced doping method was employed to incorporate phosphorus into an insulating monocrystalline diamond at ambient temperature and pressure conditions. Pulsed laser beams with nanosecond duration (20 ns) were irradiated on the diamond substrate immersed in a phosphoric acid liquid, in turns, and a thin conductive layer was formed on its surface. Phosphorus incorporation in the depth range of 40-50 nm below the irradiated surface was confirmed by secondary ion mass spectroscopy (SIMS). Electrically, the irradiated areas exhibited ohmic contacts even with tungsten prober heads at room temperature, where the electrical resistivity of irradiated areas was greatly decreased compared to the original surface. The temperature dependence of the electrical conductivity implies that the surface layer is semiconducting with activation energies ranging between 0.2 eV and 54 meV depending on irradiation conditions. Since after laser treatment no carbon or graphitic phases other than diamond is found (the D and G Raman peaks are barely observed), the incorporation of phosphorus is the main origin of the enhanced conductivity. It was demonstrated that the proposed technique is applicable to diamond as a new ex situ doping method for introducing impurities into a solid in a precise and well-controlled manner, especially with electronic technology targeting of smaller devices and shallower junctions.

We demonstrated that p- and n-type activation layers can be formed in Si films by laser doping with H3PO4 solution and Al2O3 sol coating. The phosphorus and aluminum concentrations at the laser doped region were found to be over 1019 cm-3 in Si films. In addition, generations of the activation carriers for n- and p-type layers were confirmed by Hall effects measurement. In this study, the characteristic of CMOS invertors fabricated by laser doping are presented.

We developed a novel KrF excimer laser doping system for 4H-SiC power devices, and demonstrated laser doping of 4H-SiC with Al thin film deposited on the surface. As seen from the results of the Al depth profile, high concentration implantation (~ 1021 cm-3 at the surface) of Al was achieved by laser ablation of the Al thin film. A high, built-in-potential (~3.5 V) of the pn junction diode was clearly seen in the I-V curve. In addition, the contact resistivity of the deposited Al/Ti electrodes on the surface was 1.9 × 10−4 Ωcm2 by TLM (Transmission Line Model). It was confirmed that a high concentration of Al doping and low contact resistivity were achieved by the KrF excimer laser doping system.

Al doping into 4H-SiC performed by irradiating pulse-width-expanded excimer laser to an Al film deposited on the 4H-SiC surface is investigated. An optical pulse stretcher was constructed to produce the laser pulse whose peak intensity was reduced as half as that of the original pulse and pulse width was expanded from 55 ns to 100 ns. The irradiation of the expanded pulses is found to reduce the ablation of the materials from the surface and enable irradiation of multiple shots. As the result, doping depth of Al is significantly increased. The multiple shots of the expanded pulses is also fund to decrease the sensitivity to spatial non-uniformity of laser intensity and increase the uniformity of doped region.

A singlecrystalline diamond (100)(Ib) plate immersed in 2% boric acid was irradiated by 193-nm ArF excimer laser beams for the formation of conductive layers on the surface of an insulating diamond substrate. From current-voltage measurements of the irradiated areas, it was confirmed that semiconducting layers with high conductivities are formed on the diamond surface. It was possible to form ohmic contacts by directly touching tungsten probes with the layer surface. Since Raman spectra exhibited only peaks due to diamond and no peaks due to amorphous carbon, the drastically enhanced conductivity is not attributed to amorphous carbon formation but due to the incorporation of boron atoms into the diamond subsurface from the dopant acid. Secondary ion mass spectrometric depth profile showed the incorporation of boron atoms up to 40 nm depths from the surface. From cathodoluminescence measurements at low temperatures, it was difficult to detect clear peaks for the substitutional incorporation of boron atoms into diamond lattices, which could be attributed to the small thickness of the doped layer for detection. The proposed technique is a new potential method for shallow doping and formation of conductive layers on singlecrystalline diamond surfaces.

Cubic silicon carbide (3C-SiC) films were grown by pulsed laser deposition (PLD) on magnesium oxide [MgO (100)] substrates at a substrate temperature of 800°C. Besides, p-type SiC was prepared by laser assisted doping of Al in the PLD grown intrinsic SiC film. The SiC phases, in the grown thin films, were confirmed by x-ray diffraction (XRD), Si–C bond structure is identified by Fourier-transform infrared spectroscopy spectrum analysis. Measurements based on the XRD and Raman scattering techniques confirmed improvement in crystallization of 3C-SiC thin films with the laser assisted doping. The studies on I–V characteristics by two probe technique, elemental analysis by energy dispersion spectrum, binding energy by x-ray photoelectron spectroscopy and carrier concentration by Hall effect, ensured Al doping in SiC thin film. From the UV–visible NIR spectroscopic analysis, the optical bandgap of the PLD grown 3C-SiC was obtained. Numerical analysis of temperature and carrier concentration distribution is simulated to understand the mechanism of laser assisted doping.

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 (

We demonstrate a radiation hydrodynamic simulation of optical vortex pulse-ablated microcone structures on silicon (Si) substrates. Doughnut-shaped craters were formed by single pulse irradiation on the Si substrate, and a twisted cone structure with a height of 3.5 µm was created at the center of the irradiation spot by the circularly polarized optical vortex pulse. A two-dimensional (2-D) radiation hydrodynamic simulation reproduced the cone structure well with a height of 3 µm. The central part of the incident laser power was lowered from the initial profile due to plasma shielding over the laser pulse duration for an inverted double-well laser profile. The acute tip shape of the silicon surface can survive over the laser irradiation period.

One option in enhancing metal-oxide-semiconductor transistor devices is by replacing silicon with high-mobility material of germanium. However, fabrication of Ge np junction faces low dopant activation problem due to the interaction between dopant and defect that was originated from ion implantation, during thermal annealing process results in dopant deactivation. Eventually, series resistance of np junction between source and drain regions will increase and affect the device drive current. Therefore, minimizing junction resistance remains an important issue to be solved. In this work, ultrafast/high temperature excimer laser of KrF was adopted for post-implantation annealing process in order to achieve high activation level. Laser energy fluences and shot numbers were varied between 100–2000 mJ/cm2 and 1–1000 shots, respectively to investigate the influence of laser parameter to the np junction resistance value, surface morphology and recrystallization. It is found that resistance lower than 300 Ω can be obtained when annealing the substrate between 500–1000 mJ/cm2 with shot number up to two. Taking into consideration on the morphological and structural analyses leads to the conclusion that an optimum parameter for LTA in the sample implanted with phosphorus at higher energy/dose concentration of 40 keV/6.0×1014 cm−2 is 700 mJ/cm2, with shot number of two.

Selective laser annealing system was developed to realize fabrications of low-temperature poly-Si thin-film transistors (TFTs) even for large substrate, while the conventional excimer laser annealing system has the limitation in substrate size due to the difficulty in obtaining uniform beam line. In this paper, this new system was applied to fabricate poly-Si TFTs, using two laser exposure methods such as the static exposure and the scan exposure. Grain size increased as the laser energy density increased, and TFTs with the field-effect mobility larger than 100 cm2V−1s−1 with the ON– OFF ratio of drain current of approximately 106 could be obtained. Furthermore, for the scan exposure, periodic grain structure was observed resulting from the lateral solidification. In this condition, variations of electrical properties of TFT could be reduced compared to the case of the static exposure.

Submicrometer spherical particles (SMSPs) are reported to be fabricated by pulsed laser irradiation with a frequency of 10 or 30 Hz onto raw nanoparticles dispersed in liquid. Here, the effect of the pulse frequency on particles obtained by laser irradiation onto the suspension in a vessel, especially at higher pulse frequencies up to 800 Hz, is investigated. At 200 Hz or lower, SMSPs of similar size can be fabricated, as at 10 or 30 Hz, by the same number of pulses. This indicates that the time required for particle fabrication can be greatly reduced and production efficiency can be improved using a high-frequency laser. In contrast, at 400 Hz or above, nanospherical particles (NSPs) are formed in addition to SMSPs, and the mass fraction of SMSPs is drastically decreased. This result suggests that consecutive laser pulse irradiation induces heat accumulation in particles and suspensions, resulting in a temperature increase and partial evaporation of the particles at 400 Hz or above. From the temperature increase of the suspension, the local temperature of the liquid surrounding the particles is believed to be increased by heat dissipation from the heated particles. Calculations suggest that an increase in the local liquid temperature would cause further heating of the particles.

Al is doped into 4H-SiC by irradiating pulsed KrF excimer laser to 4H-SiC immersed in AlCl3 aqueous solution. Impact on doping depth of the use of expanded laser-pulse width is investigated. Expanded laser pulse is produced by splitting and recombining the laser beam with mirrors. The laser pulse width was expanded from its original width of 55–100 ns, while the peak power of the expanded pulse is as half as that of the original pulse under the same laser fluence. Multiple shots of the expanded laser pulses increased the doping depth at the Al concentration of 1×1016 /cm3 to 100 nm from 30 nm of the single shot of the original short, high-peak power laser. The increased doping depth could be due to enhanced diffusion by extra vacancies generated by the repeated laser irradiations. Due to the smaller laser peak power, the expanded pulse laser can suppress damage generation under multiple laser shots and, as a result, leakage current of the pn junction diode is kept low.

Sub-micrometer spherical particles can be synthesized by irradiating particles in a liquid with a pulsed laser (pulse width: 10 ns). In this method, all of the laser energy is supposed to be spent on particle heating because nanosecond heating is far faster than particle cooling. To study the cooling effect, sub-micrometer spherical particles are fabricated by using a pulsed laser with longer pulse widths (50 and 70 ns). From the increase in the laser-fluence threshold for sub-micrometer spherical particle formation with increasing pulse width, it is concluded that the particles dissipate heat to the surrounding liquid, even during several tens of nanoseconds of heating. A particle heating-cooling model considering the cooling effect is developed to estimate the particle temperature during laser irradiation. This model suggests that the liquid surrounding the particles evaporates, and the generated vapor films suppress heat dissipation from the particles, resulting in efficient heating and melting of the particles in the liquid. In the case of small particle sizes and large pulse widths, the particles dissipate heat to the liquid without forming such vapor films.

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.

Al doping of 4H-SiC with high surface concentration and deep depth profile is found to be realized by irradiating single-pulse excimer laser to an Al film deposited on the surface. Optical emission spectra suggest that high-temperature molten Al is produced behind the laser-generated high-density Al plasma and Al is diffused from the molten Al into 4H-SiC. The Al doping depth reaches to ~200 nm by irradiating a single laser pulse. A pn junction diode fabricated by the doping with the molten Al shows on/off ratio over 10 orders of magnitude.

In this paper, we report on the characterization of Si thin films doped by wet-chemical laser processing. Using this method, implantation and dopant activation can be performed simultaneously. After laser doping, the mobility, carrier concentration, and resistivity of the films were 74 cm2/V·s, 5.5 × 1017 cm−3, and 0.15 Ω·cm, respectively.

Mg-doped p-type semiconducting aluminium-gallium-nitride hole source layer (p-AlGaN HSL) materials are quite promising as a source of hole ‘p’ carriers for the ultraviolet-B (UVB) light-emitting diodes (LEDs) and laser diodes (LDs). However, the p-AlGaN HSL has a central issue of low hole injection due to poor activation of Mg atoms, and the presence of unwanted impurity contamination and the existence of a localized coherent state. Therefore, first the impact of the Mg level on the crystallinity, Al composition and relaxation conditions in the p-AlGaN HSL were studied. An increasing trend in the lattice-relaxation ratios with increasing Mg concentrations in the p-AlGaN HSL were observed. Ultimately, a 40%–60% relaxed and 1.4 μm thick p-AlGaN HSL structure with total threading dislocation densities (total-TDDs) of approximately ∼8–9 × 108 cm−2 was achieved, which almost matches our previous design of a 4 μm thick and 50% relaxed n-AlGaN electron source layer (ESL) with total-TDDs of approximately ∼7–8 × 108 cm−2. Subsequently, structurally a symmetric p–n junction for UVB emitters was accomplished. Finally, the influence of excimer laser annealing (ELA) on the activation of Mg concentration and on suppression of unwanted impurities as well as on the annihilation of the localized energy state in the p-AlGaN HSL were thoroughly investigated. ELA treatment suggested a reduced Ga–N bonding ratio and increased Ga–O, as well as Ga–Ga bonding ratios in the p-AlGaN HSL. After ELA treatment the localized coherent state was suppressed and, ultimately, the photoluminescence emission efficiency as well as conductivity were drastically improved in the p-AlGaN HSL. By using lightly polarized p-AlGaN HSL assisted by ELA treatment, quite low resistivity in p-type AlGaN HSL at room temperature (hole concentration is ∼2.6 × 1016 cm−3, the hole mobility is ∼9.6 cm2 V1 s−1 and the resistivity is ∼24.39 Ω. cm) were reported. ELA treatment has great potential for localized activation of p-AlGaN HSL as well as n- and p-electrodes on n-AlGaN and p-AlGaN contact layers during the flip-chip (FC) process in low operating UVB emitters, including UVB lasers.

Impact of laser doping on the formation of ohmic contacts to 4H-SiC has been investigated. The laser doping was performed by irradiating pulse-width stretched KrF excimer laser to an Al film coated on the surface of 4H-SiC. Doping and contact formation on the carbon face of 4H-SiC were investigated. The doping was carried out while keeping the sample at room temperature. It is found that the laser doping is able to introduce Al up to a concentration as high as 5×1021 cm-3. As a result of heavy doping, the contact made of Ti/Al metallization provides the ohmic contact whose specific contact resistance as low as 4.0×10-6 Ωcm2 without additional heat treatment. The specific contact resistance is lower than that reported for ohmic contacts formed by using ion implantation.

We characterize poly-Si thin films doped by KrF excimer laser irradiation with a phosphoric-acid coating. In this method, implantation and dopant activation can be performed simultaneously without damage of the poly-Si crystallization. After the laser doping, the mobility, carrier concentration, activation ratio, and resistivity of poly-Si were 61 cm2/Vs, 1.5×1018 cm−3, 14.6 %, and 0.08 Ω.cm, respectively.

The emphasis on ubiquitous technology means that future technological applications will depend heavily on transparent conducting materials. To facilitate truly ubiquitous applications, transparent conductors should be fabricated at low temperatures (

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.

Higher carrier mobility in germanium has made germanium as a favorable candidate to replace silicon as a device substrate for a high-performance device. Further optimization on fabrication process parameters in germanium involving ion-implantation and thermal annealing is important to form a highly activated np junction. Co-implantation technique has prompted interest due to its reported stress-induced activation; which may be due to the implementation of two atoms different in size. Combining with ultra-fast/high temperature of laser thermal annealing may promotes the improvement in activation and damage removal. This works focused on introducing stress to the germanium substrate through co-implantation of dopant ions, follows by laser thermal annealing to activate and remove the implanted damages. It is found that Raman shift of the annealed co-implanted sample can be observed with 0.2% increase in the strain value, when comparing to the single implanted sample. 12% improvement of sheet resistance can also be observed, which may be related due to the increase in stress.

We have investigated thermoelectric (TE) properties of poly-Ge}_{1-x}Sn}_{x} layers prepared with pulsed laser annealing in water. Even for polycrystalline layers, relatively high power factors of 0.37 and 0.92 mWK−2m−1 were obtained for p- and n-type poly-Ge}_{1-x}Sn}_{x} layers, respectively. The Ge}_{1-x}Sn}_{x}-based TE generator has been firstly fabricated blow the process temperature of 300 °C.

Introduction Formation of crystalline GeSn film on insulator with high Sn concentration exceeding thermal equilibrium solid-solubility is strongly expected to realize high-speed thin film transistors. To explore non-thermal equilibrium processing [1], we examined crystallization of amorphous-GeSn (a-GeSn) with various modulated Sn concentration by pulsed laser annealing (PLA). In the present study, we focus on the influence of the Sn concentration on crystallization of a-GeSn by PLA. Experimental Procedure Schematic sample structure and PLA conditions are shown in Fig.1. A-Ge1-xSnx (0≦x≦0.2) films (thickness: 100 nm) were deposited on quartz substrates by a molecular beam technique. These samples were irradiated with a pulsed laser (energy : 10 - 230 mJ/cm2, pulse period : 1 sec, pulse number : 100 shot). The laser annealed regions were analyzed by Nomarski microscopy and Raman scattering spectroscopy. Results and Discussion Nomarski micrograph and Raman spectra of Ge0.8Sn0.2 samples before and after PLA with various energy are summarized in Fig. 2. In the samples after PLA, the contrast-changed regions were observed, compared with the as-deposited sample. Here, the contrast becomes stronger with increasing energy from 50 mJ/cm2 to 170 mJ/cm2, and finally the GeSn layer was damaged for energy of 230 mJ/cm2. Raman spectra reveales that Ge0.8Sn0.2 is crystallized on insulating substrates by 50 - 170 mJ/cm2 PLA. The process-window to achieve crystalline GeSn is summarized in Fig. 3(a), where the energy for starting crystallization and the energy just before damaging are indicated as Ecryst. and Edamage , respectively. Substitutional Sn concentration estimated from shift of Ge-Ge peak obtained by Raman measurements is shown in Fig. 3(b). The process window necessary for crystallization is significantly expanded by introducing Sn, i.e. 16 mJ/cm2 for Ge, ~ 130 mJ/cm2 for GeSn. High Sn concentration exceeding thermal equilibrium solid-solubility is obtained by PLA, for all GeSn samples. Interestingly, for samples with initial Sn concentration of 5 % and 10 %, almost all Sn atoms are incorporated into substitutional site, while for 20 % sample, only half of Sn atoms are incorporated into substitutional site. The detailed physics will be discussed in the presentation. References [1] M. Kurosawa, et al., Appl. Phys. Lett. 104, 061901 (2014). Figure 1

We report nitrogen (N) doping of 4H-SiC by KrF excimer laser irradiation in liquid N2. In comparison to phosphorus (P) doping performed using phosphoric acid solution, the liquid-N2 immersion-laser doping can introduce N atoms deeper (~ 1 μm depth) into the 4H-SiC, which results in reduction of doped layer resistance by approximately 3 orders of magnitude. Doping is shown to proceed by the thermal diffusion of species, while loss of the host material from the surface by ablation takes place at the same time. Chemical analysis shows that high density carbon (C) vacancies are generated in the N doped region, which suggests enhanced diffusion of N assisted by the presence of C vacancies. pn junction diodes are formed by using the N doping technique. Turn-on voltage is ~ -3V, which is reasonable for a pn junction diode of 4H-SiC.

A vertically aligned ZnO nanowall arrays have been synthesized on a patterned ZnO buffer layer using an interference laser beam. The average height and thickness of the ZnO nanowall were 4 μm and 200 nm, respectively. Room-temperature ultraviolet (UV) lasing was obtained from single piece of ZnO nanowall detached from the substrate. The threshold power density for lasing was estimated to be about 80 kW/cm2. In addition, UV lasing from vertically aligned ZnO nanowall was also observed owing to the presence of holes. The lasing spectra had no regularity in the mode spacing and many different spatial modes, suggesting that the action was supported by the random lasing mechanism. The threshold power density for lasing was about 300 kW/cm2, which was much higher than that of the single piece of ZnO nanowall because of the leakage of the light into buffer layer.

We succeed in fabricating Sb-doped ZnO nanowires by laser doping using Sb nanoparticles (Sb NPs). Vertically aligned ZnO nanowires with a diameter of 100 nm were synthesized by the nanoparticles-assisted pulsed laser deposition. Sb NPs were prepared by laser ablation in liquid. The average size of 50 nm Sb NPs was successfully fabricated by laser ablation in ethanol. Subsequently, laser doping was performed by irradiating Nd:YAG laser beam (355 nm) in Sb-dispersed ethanol. After laser doping, the tip of ZnO nanowires was slightly deformed into spherical shape by laser heating. A rectifying property with a threshold voltage of 4.5 V was observed between n-type ZnO nanowires and Sb-doped ZnO nanowires.

In this paper, we report on super low temperature doping of phosphorus to poly-Si thin films using XeF excimer laser irradiation in a phosphoric acid solution. In this method, the implantation of P atoms and dopant activation can be performed simultaneously. We prepared poly-Si films with a thickness of 50 nm, and these films were crystallized using XeF excimer laser annealing. After laser doping, the concentration of P atoms in the poly-Si films was approximately 3.5 × 1018 cm−3, and the resistance of the poly-Si films decreased by approximately 0.003 times as compared with that before laser doping.

We have succeeded in fabricating zinc oxide (ZnO) microsphere by laser ablation in the air and demonstrated ultraviolet whispering gallery mode lasing from an optically pumped ZnO microsphere. However, fabricated microspheres could not be controlled in size, and ejection direction of microsphere was random, because the generation mechanism was attributed to the droplet ejection by laser ablation. In this report, the effect of pulse duration on microsphere generation was investigated, and we introduced optical vortex to control the size and the ejection direction of droplets. The behavior of ablated target was visualized using a high-speed camera. As a result of time-resolved observation, it was found that many ZnO microspheres can be efficiency generated by the long pulse laser irradiation. In addition, it was observed that droplets were scattered randomly by Gaussian beam irradiation. In the case of optical vortex irradiation, straight flight of the droplet was achieved. Furthermore, the size of droplets changed with pulse energy and ablation spot size with optical vortex. From these results, controlled fabrication of ZnO microspheres is expected with optical vortex laser ablation.

Low-temperature (≤200°C) formation of GeSn (substitutional Sn concentration: >8%) films on insulator is desired to realize high-speed thin film transistors (TFTs) and high-efficiency optical devices on flexible plastic substrates (softening temperature: ∼200°C). This is because GeSn (substitutional Sn concentration: >8%) has higher carrier mobility than Si and Ge due to the direct-transition energy band structure with smaller effective mass of carriers.

Germanium (Ge) is a potential candidates to replace silicon (Si) due to its higher carrier mobility, which is the key point for realizing device high-drive-current. However, fabricating highly activated np junction in Ge is challenging due to the severe damages introduced from ion-implantation interact with dopant during subsequent annealing process, and results in dopant deactivation. Further optimization of fabrication process parameters is needed to overcome this problem. Co-implantation technique has gained attention due to its stress-induced carrier activation by implanting two atoms with different size. Combining with laser thermal annealing promise further improvement in activation and recrystallization. In this work, co-implantation of phosphorus (P) and tin (Sn) were performed, followed by KrF laser thermal annealing, to form an np junction in Ge. Laser fluence was varied to achieve np junction with higher activation and recrystallization. It is found that high degree of recrystallization was obtained in higher-fluence annealed sample, with 40% decrease of sheet resistance compare to those of lower-fluence annealed sample. Raman peak shift (≈ 3.5 cm−1) was also observed in the higher-fluence annealed sample, suggesting increase of localized strain in the sample.

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.

Zinc oxide (ZnO) nanocrystals, which are characterized by their configurations and fine structures, are unique oxide semiconductors. In this report, it is demonstrated that the number density of ZnO nanowires can be controlled by proper treatments of the buffer layer with ultraviolet laser irradiation. ZnO nanowires were synthesized on the locally laser-irradiated ZnO buffer layer using nanoparticle-assisted pulsed-laser deposition (NAPLD). The number density of ZnO nanowires decreased in the region laser-irradiated with