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We report the fabrication of p-n+ diamond homojunction through an innovative approach of laser irradiation in liquid-ambient. A shallow phosphorus-doped layer with a high electric conductivity is processed on top of a p-type diamond substrate to form the p-n+ homojunction. The current–voltage measurements at room temperature confirmed high conductivity of the induced n+ layer and showed exceptional rectification properties with an ideality factor of 1.07, excellent low on-resistance of 3.7 × 10−2 Ωcm2, and current density over 260 Acm−2 at forward-biasing of 10 V. Furthermore, undetectable leakage-current provides a rectification ratio exceeding 1010 at ±6 V, promoting the junction in UV detection applications.

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.

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.

Low temperature (8%) on insulating substrates is essential to realize next generation flexible electronics. To achieve this, a growth method of high quality GeSn films on insulating substrates by combination of laser irradiation and subsequent thermal annealing is developed. Here, the laser fluence is chosen as weak, which is below the critical fluence for crystallization of GeSn. It is clarified that for samples irradiated with weak laser fluence, complete crystallization of GeSn films is achieved by subsequent thermal annealing at ∼170 oC without incubation time. In addition, the quality of GeSn films obtained by this method is higher compared with conventional growth techniques such as melting growth by pulsed laser annealing or solid-phase crystallization (SPC) without pre-laser irradiation. Substitutional Sn concentrations in the grown layers estimated by Raman spectroscopy measurements are 8-10%, which far exceed thermal equilibrium solid-solubility of Sn in Ge (∼2%). These phenomena are explained by generation of a limited number of nuclei by weak laser irradiation and lateral SPC by subsequent thermal annealing. This method will facilitate realization of next-generation high performance devices on flexible insulating substrates.

SiO2 nanoporous films have recently gained significant popularity as low-k dielectric constant insulating films. In this study, we demonstrated the fabrication of a low-k SiO2 nanoporous film consisting of SiO2 nanoparticles by pulsed laser deposition. However, to optimize the growth conditions of nanoporous films, it is important to understand the spatial and size distribution of nanoparticles produced by laser ablation. Here, we visualized laser-ablated SiO2 nanoparticles using a two-dimensional laser scattering imaging technique and investigated the influence of gas species and pressure on the spatial distribution of the nanoparticles in the gas phase. After the decay of the plasma emission within several microseconds, a spherical-shaped scattering image depicting the spatial distribution of SiO2 nanoparticles was obtained from a delay time of approximately 10 ms. In Ar gas, the sphericalshaped distribution of SiO2 nanoparticles changed to an ellipsoidal shape with increasing pressure, whereas in O2 gas, it changed a mushroom-like shape. These results show that the gas species and pressure are dominant parameters affecting the spatial distribution of nanoparticle formation. [ABSTRACT FROM AUTHOR]

Low temperature (<200 °C) crystallization of GeSn (substitutional Sn concentration: >8%) on insulating substrates is essential to realize next generation flexible electronics. To achieve this, a growth method of high quality GeSn films on insulating substrates by combination of laser irradiation and subsequent thermal annealing is developed. Here, the laser fluence is chosen as weak, which is below the critical fluence for crystallization of GeSn. It is clarified that for samples irradiated with weak laser fluence, complete crystallization of GeSn films is achieved by subsequent thermal annealing at ~170 °C without incubation time. In addition, the quality of GeSn films obtained by this method is higher compared with conventional growth techniques such as melting growth by pulsed laser annealing or solid-phase crystallization (SPC) without pre-laser irradiation. Substitutional Sn concentrations in the grown layers estimated by Raman spectroscopy measurements are 8-10%, which far exceed thermal equilibrium solid-solubility of Sn in Ge (~2%). These phenomena are explained by generation of a limited number of nuclei by weak laser irradiation and lateral SPC by subsequent thermal annealing. This method will facilitate realization of next-generation high performance devices on flexible insulating substrates. [ABSTRACT FROM AUTHOR]

We have succeeded in growing the ZnO spherical microcrystals by a simple laser ablation in air, and we have obtained ultraviolet (UV) whispering-gallery-mode (WGM) lasing from the sphere under pulsed laser excitation. In this growth technique, a solid ZnO target is rapidly heated by laserinduced plasma, and melted target is splashed from the irradiated spot as droplets. Then, the droplets are crystallized into spherical shapes by the surface tension during the dropping process. This rapid melting and solidifying process may be effective for doping impurities into ZnO. In this study, we fabricated P-, Sb-, and Mg-doped ZnO microspheres, and investigated their structures and optical properties. A blue-shift of UV WGM lasing from Mg-doped ZnO microsphere was obtained, indicating that the band-gap engineering of ZnO microsphere grown by the simple ablation technique was achieved. [ABSTRACT FROM AUTHOR]

In this report, we propose a direct patterning method of graphene on the SiC(0001) surface by KrFexcimer- laser irradiation. In this method, Si atoms are locally sublimated from the SiC surface in the laser-irradiated area, and direct graphene growth is induced by the rearrangement of surplus carbon on the SiC surface. Using Raman microscopy, we demonstrated the formation of graphene by laser irradiation and observed the growth process by transmission electron microscopy and conductive atomic force microscopy. When SiC was irradiated by 5000 shots of the laser beam with a fluence of 1.2 J/cm², two layers of graphene were synthesized on the SiC(0001) surface. The number of graphene layers increased from 2 to 5-7 with an increase in the number of laser shots. Based on the results of conductive-atomic force microscopy measurements, we conclude that graphene formation was initiated from the step area, after which the graphene grew towards the terrace area by further Si evaporation and C recombination with increasing laser irradiation. [ABSTRACT FROM AUTHOR]

We have investigated phosphorus (P) doping into Ge(001) surfaces by using ultraviolet laser irradiation in phosphoric acid solution at room temperature. We demonstrated that the diffusion depth of P in Ge and the concentration of electrically activated P can be controlled by the number of laser shots. Indeed, a high concentration of electrically activated P of 2.4 x 1019cm-3 was realized by 1000-times laser shots at a laser energy of 1.0 J/cm², which is comparable or better than the counterparts of conventional n-type doping using a high thermal budget over 600 °C. The generation current is dominant in the reverse bias condition for the laser-doped pn-junction diodes independent on the number of laser shots, thus indicating low-damage during the pn-junction formation. These results open up the possibility for applicable low thermal budget doping process for Ge-based devices fabricated on flexible substrates as well as Si electronics. [ABSTRACT FROM AUTHOR]

To realize next-generation flexible thin-film devices, solid-phase crystallization (SPC) of amorphous germanium tin (GeSn) films on insulating substrates combined with seeds formed by laser annealing (LA) has been investigated. This technique enables the crystallization of GeSn at controlled positions at low temperature (~180 °C) due to the determination of the starting points of crystallization by LA seeding and Sn-induced SPC enhancement. The GeSn crystals grown by SPC from LA seeds showed abnormal lateral profiles of substitutional Sn concentration. These lateral profiles are caused by the annealing time after crystallization being a function of distance from the LA seeds. This observation of a post-annealing effect also indicates that GeSn with a substitutional Sn concentration of up to ~10% possesses high thermal stability. These results will facilitate the fabrication of next-generation thin-film devices on flexible plastic substrates with low softening temperatures (~250 °C). [ABSTRACT FROM AUTHOR]

We investigate Sn incorporation effects on the growth characteristics of Ge-rich Ge1-xSnx (x<0.02) on SiO2 crystallized by pulsed laser annealing (PLA) in air and water. Despite the very low Sn content of 2%, Sn atoms within the GeSn layers play a role in preventing ablation and aggregation of the layers during these PLA. Raman and electron backscatter diffraction measurements demonstrate achievement of large-grain (~800 nmϕ) growth of Ge0.98Sn0.02 polycrystals by using PLA in water. These polycrystals also show a tensile-strain of ~0.68%. This result opens up the possibility for developing GeSn-based devices fabricated on flexible substrates as well as Si platforms. [ABSTRACT FROM AUTHOR]

We have succeeded in synthesizing ZnO nano/microspheres by a simple laser ablation method in the air and demonstrated whispering-gallery-mode (WGM) lasing from the ZnO sphere excited by a pulsed-ultraviolet laser beam. The spheres with diameters of up to 10μm were simply prepared by laser ablation of a ZnO sintered target by a Q-switched Nd:YAG laser in the air. In this study, we succeeded synthesizing large microspheres with diameters of larger than 20μm by the Nd:YAG laser without Q-switching. The mode spacing of the large sphere was in good agreement with the WGM theory. [ABSTRACT FROM AUTHOR]

We demonstrate the rapid (<100 ns) activation and enhancement of solution-processed InZnO thin-film transistors (TFT) via a photo-assisted process: excimer laser annealing (ELA). A single shot is sufficient to enhance mobility from 0.19 cm2 V−1 s−1 to 3.91 cm2 V−1 s−1. Through multiphysics simulation, we confirmed that the process is instantaneous (<100 ns) and induces low substrate temperature suitable for flexible substrates. Analysis of optical properties, elemental concentration, and bonding changes after ELA revealed an improved metal-oxide formation and effective reduction of precursor-related impurities and oxygen vacancy traps. These demonstrate ELA’s potential for high-throughput fabrication of solution-processed devices for large-area, transparent, and flexible electronics. [ABSTRACT FROM AUTHOR]

Laser-assisted doping combined with annealing technique is used in selective areas to form a p–n junction on a SiC thin film grown by the pulsed laser deposition on a Si substrate at a temperature of 800 °C. This approach in an aluminum chloride solution and a phosphoric solution has resulted in p-SiC/n-Si and n-SiC/p-Si hetero-structures, respectively. Further, a functional in-plane p–n junction is realized side-by-side on the post-deposited SiC thin film. I–V characteristics by two probe technique showed the p–n diode characteristics. Blue light (400 nm) electroluminescence from the p–n junction on SiC thin film was observed in the forward biased condition. Further, an improvement in the I–V reverse characteristics was observed by illuminating the p–n SiC thin film with green/blue light. [ABSTRACT FROM AUTHOR]

The effect of laser doping on the contact resistance of ohmic contact to 4H-SiC has been investigated. Laser doping was performed by irradiating a pulse-width stretched KrF excimer laser to an Al film coated on the surface of 4H-SiC. Doping and contact formation on the C-face were investigated. The doping was carried out while keeping the sample at room temperature. The experimental results suggest that the contact made of Ti/Al can achieve specific contact resistance as low as 4.0 × 10−6 Ωcm2 without additional heat treatment. The contact resistance is lower than that reported for ohmic contacts formed using ion implantation. [ABSTRACT FROM AUTHOR]

A thin-film thermoelectric generator composed of p- and n-type poly-Ge1−xSnx (x ∼ 0.02) on a Si(001) covered with SiO2 has been successfully fabricated by low thermal budget processes (under 300 °C) and demonstrated for the first time. Both the crystallization and dopant activation were simultaneously performed using pulsed UV laser irradiation in flowing water. A recorded activation ratio of Sb in the poly-Ge1−xSnx enabled a relatively high power factor (9.2 μ Wcm−1 K−2 at RT), which is comparable to the counterparts of n-type Ge1−xSnx layers epitaxially grown on InP(001). [ABSTRACT FROM AUTHOR]

We propose a simple and easy electrode formation technique on nanopolycrystalline diamond (NPD) synthesized by a high-temperature and high-pressure technique. The stronger light absorption nature of NPD than of standard transparent diamond enables the laser irradiation process on NPD. Pulsed laser irradiation using an ArF excimer laser under atmospheric condition drastically reduced the resistance of the NPD surface by forming graphite. Repetition of the laser irradiation reduced the resistance, showing a resistance of 300 Ω for the laser-irradiated area of 100 × 150 µm2. These results indicate the applicability of pulsed laser irradiation to an NPD apparatus having a conductive electrode, as well as electronic device processes. [ABSTRACT FROM AUTHOR]

A low-temperature process for the formation of heavily doped polycrystalline Ge (poly-Ge) layers on insulators is required to realize next-generation electronic devices. In this study, we have systematically investigated pulsed laser annealing (PLA) in flowing water for heavily doped amorphous Ge1−xSnx layers (x ≈ 0.02) with various dopants such as B, Al, Ga, In, P, As, and Sb on SiO2. It is found that the dopant density after PLA with a high laser energy is reduced when the oxidized dopant has a lower oxygen chemical potential than H2O. As a result, for the p-type doping of B, Al, Ga, and In, we obtained a high Hall hole density of 5 × 1019 cm−3 for PLA with a low energy. Consequently, the Hall hole mobility is limited to as low as 10 cm2 V−1 s−1. In contrast, for As and Sb doping, because the density of substitutional dopants does not decrease even after PLA with a high energy, we achieved a high Hall electron density of 6 × 1019 cm−3 and a high Hall electron mobility simultaneously. These results indicate that preventing the oxidation of dopant atoms by water is an important factor for achieving heavy doping using PLA in water. [ABSTRACT FROM AUTHOR]

This paper focuses on the bonding interface of LiNbO3 and Si wafers bonded by laser irradiation. The nanostructure and composite distribution across the bonding interface were investigated. The experimental interface analysis showed that no cracks or voids were formed at the nanolevel. It was also found that the bonding interface had a disordered amorphous layer containing Nb, O, and Si. This indicates that a strong bond was achieved because fusion bonding proceeded at the interface between LiNbO3 and Si. In addition, the effectiveness of this bonding method for the wafer-level bonding of LiNbO3 and Si was demonstrated. [ABSTRACT FROM AUTHOR]

The formation of perhydropolysilazane (PHPS)-based SiO2 films by CO2 laser annealing is proposed. Irradiation with a CO2 laser with optimum fluence transformed a prebaked PHPS film into a SiO2 film with uniform composition in the thickness direction. Polycrystalline silicon thin-film transistors (poly-Si TFTs) with a SiO2 film as the gate insulator were fabricated. When the SiO2 film was formed by CO2 laser annealing (CO2LA) at the optimum fluence of 20 mJ/cm2, the film had fewer OH groups which was one-twentieth that of the furnace annealed PHPS film and one-hundredth that of the SiO2 film deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethyl orthosilicate (TEOS). The resulting TFTs using PHPS showed a clear transistor operation with a field-effect mobility of 37.9 ± 1.2 cm2 V−1 s−1, a threshold voltage of 9.8 ± 0.2 V, and a subthreshold swing of 0.76 ± 0.02 V/decade. The characteristics of such TFTs were as good as those of a poly-Si TFT with a SiO2 gate insulator prepared by PECVD using TEOS. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a bonding method in ambient air using laser irradiation to the face-to-face interface of dissimilar materials. This method is performed while keeping whole wafers of the materials at room temperature. We demonstrate the bonding of LiNbO3 to Si using pulsed nanosecond green laser irradiation. Laser use can minimize thermal stress owing to a large thermal expansion mismatch. The bonding characteristic obtained by an irradiation laser up to 2.5 J/cm2 in fluence is investigated. It is found that a LiNbO3 chip is strongly bonded to a Si chip by setting the laser fluence at the optimum range. A bond strength of over 2 MPa, which may be enough for the device applications, can be obtained. [ABSTRACT FROM AUTHOR]