Nanosecond Green Laser Research Articles

High-performance n-channel polycrystalline germanium thin-film transistors via continuous-wave laser crystallization and green nanosecond laser annealing for source and drain dopant activation

High-quality polycrystalline germanium (poly-Ge) films have been successfully fabricated via the continuous-wave laser crystallization (CLC) process. Grain sizes as large as 0.8 μm were obtained for the poly-Ge films by CLC at 5.7 W. Furthermore, the source and drain dopants could then be effectively activated by green nanosecond laser annealing (GNS-LA). Consequently, n-channel CLC Ge thin-film transistors (TFTs) with a high field-effect mobility of 576 cm2 V−1 s−1 were demonstrated for an effective channel width of 0.86 μm and a channel length of 0.5 μm. It is shown that CLC combined with GNS-LA is effective for attaining high-performance n-channel poly-Ge TFTs.

Antireflective copper surfaces fabricated by low-cost nanosecond lasers for efficient photothermal conversion and desalination

Surfaces with efficient photothermal conversion have great value in both science and industry. In this study, large-area hierarchical microstructures and nanostructures with high light absorptance over a wide spectrum range from ultraviolet to the near-infrared region were fabricated on copper surfaces by a low-cost green nanosecond laser system. By optimizing the morphology of laser-induced surface structures, the average light absorptance in the wavelength range of 220–800 nm and 220–2500 nm can be as high as 98.9% and 91.9%, respectively. Moreover, the laser-processed surfaces demonstrated a photothermal conversion efficiency of more than 52% under 15 sun illuminations. The authors also showed that the desalination efficiency was greatly improved when the prepared surfaces were used as the solar energy harvesting surfaces in the solar energy driven desalination system.

Rapid, high-quality microfabrication of thermoset polymer PDMS using laser-induced bubbles.

Bubbles can be formed by focusing a high-power laser in a liquid. Based on this phenomenon, the present study demonstrated a novel technique, referred to as microFabrication using Laser-Induced Bubbles (microFLIB), for the microfabrication of the thermoset polymer polydimethylsiloxane (PDMS). A conventional nanosecond green laser was focused at the interface between uncured PDMS and a metal target and scanned to generate a line of bubbles at the boundary. The hemispherical shapes of these bubbles produced a groove on the rear side of the PDMS substrate following subsequent thermal curing. After the fabrication of such specimens, metal films could be selectively deposited along the grooves by electroless plating. This process allows rapid, high-quality microfluidic fabrication with potential applications to biochips.

Space debris laser ranging with a 60 W single-frequency slab nanosecond green laser at 200 Hz

Space debris laser ranging was achieved with a 60 W, 200 Hz, 532 nm nanosecond slab, single-frequency green laser at the Shanghai Astronomical Observatory’s 60 cm satellite laser ranging system. There were 174 passes of space debris measured in 2017, with the minimum radar cross section (RCS) being 0.25 m2 and the highest ranging precision up to 13.6 cm. The RCS of space debris measured with the farthest distances in 174 passes was analyzed. The results show that the farthest measurement distance (R) and RCS (S) were fitted to R = 1388.159S0.24312, indicating that this laser can measure the distance of 1388.159 km at an RCS of 1 m2, which is very helpful to surveillance and research on low-Earth-orbit space debris.

Creation of Superhydrophobic and Superhydrophilic Surfaces on ABS Employing a Nanosecond Laser.

A nanosecond green laser was employed to obtain both superhydrophobic and superhydrophilic surfaces on a white commercial acrylonitrile-butadiene-styrene copolymer (ABS). These wetting behaviors were directly related to a laser-induced superficial modification. A predefined pattern was not produced by the laser, rather, the entire surface was covered with laser pulses at 1200 DPI by placing the sample at different positions along the focal axis. The changes were related to the laser fluence used in each case. The highest fluence, on the focal position, induced a drastic heating of the material surface, and this enabled the melted material to flow, thus leading to an almost flat superhydrophilic surface. By contrast, the use of a lower fluence by placing the sample 0.8 µm out of the focal position led to a poor material flow and a fast cooling that froze in a rugged superhydrophobic surface. Contact angles higher than 150° and roll angles of less than 10° were obtained. These wetting behaviors were stable over time.

Cavitation bubble nucleation induced by shock-bubble interaction in a gelatin gel

An optical visualization technique is developed to study cavitation bubble nucleation that results from interaction between a laser-induced shock and a preexisting gas bubble in a 10 wt. % gelatin gel; images of the nucleated cavitation bubbles are captured and the cavitation inception pressure is determined based on Euler flow simulation. A spherical gas cavity is generated by focusing an infrared laser pulse into a gas-supersaturated gel and the size of the laser-generated bubble in mechanical equilibrium is tuned via mass transfer of the dissolved gas into the bubble. A spherical shock is then generated, through rapid expansion of plasma induced by the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gel under tension that results from acoustic impedance mismatching at the bubble interface interacting with the shock. We measure the probability of cavitation inception from a series of the repeated experiments, by varying the bubble radius and the standoff distance. The threshold pressure is defined at the cavitation inception probability equal to one half and is calculated, through comparisons to Euler flow simulation, at −24.4 MPa. This threshold value is similar to that from shock-bubble interaction experiments using water, meaning that viscoelasticity of the 10 wt. % gelatin gel has a limited impact on bubble nucleation dynamics.

Laser Light Induced Transformation of Molybdenum Disulphide-Based Nanoplatelet Arrays.

One-pot hydrothermal synthesis of MoS2 nanoplatelet arrays on various substrates is perhaps the most promising approach to fabricate efficient electrocatalysts for hydrogen evolution reaction. However, the main challenges in this synthesis remain the purity and crystallinity of MoS2. In this study, we show for the first time that irradiation of amorphous, defect-rich MoS2 nanoplatelets with a green nanosecond laser at a proper irradiation dose, ca ≤0.35 J cm−2, can significantly improve the crystallinity and purity of MoS2 nanoplatelets. The effect was confirmed by Raman spectroscopy investigations demonstrating a surprising intensity increase of the A1g and modes after the laser irradiation. Further increase of irradiation energy, however, resulted in the photocorrosion and destruction of MoS2 nanoplatelets. The variation of A1g and Raman mode intensities ratio depending on the green light irradiation dose was also presented and is discussed below.

Bonding of lithium niobate to silicon in ambient air using laser irradiation

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.

High Gamma Value 3D-Stackable HK/MG-Stacked Tri-Gate Nanowire Poly-Si FETs With Embedded Source/Drain and Back Gate Using Low Thermal Budget Green Nanosecond Laser Crystallization Technology

Three-dimensional sequentially stackable high- $k$ /metal-gate-stacked tri-gate nanowire poly-Si FETs with embedded source/drain (e-S/D) and back gate were demonstrated. The highly crystallized channel, fabricated by green nanosecond laser crystallization, chemical mechanical polish, and postsurface modification processes, enhances the electrical property of the tri-gate nanowire FET. The e-S/D structure reduces the contact and series resistances caused by the nanowire structure. Thus, the fabricated n/p-type tri-gate nanowire poly-Si FETs exhibit steep subthreshold swings (96/125 mV/decade), high ON-currents (232/110 $\mu \text{A}/\mu \text{m}$ ), and $I_{{\mathrm{\scriptscriptstyle {on}}}}/I_{\mathrm{\scriptscriptstyle {OFF}}}$ ratio ( $> 10^{5})$ . Furthermore, the independent back gate with thin back gate oxide can easily adjust the threshold voltage of the tri-gate nanowire transistor and results in high gamma value (>0.05) FET realizing sequentially stacked and low $V_{\mathrm {dd}}$ (0.6 V) operable inverter.

衝撃波と気泡の干渉によるゼラチンゲルのキャビテーション初生

We experimentally and numerically study a shock-bubble interaction problem in gelatin gels. The nucleation of spherical gas bubbles is triggered by focusing an infrared laser pulse into gassupersaturated gels and the radius of the nucleated bubble is controlled by mass transfer of the dissolved gases. A spherical shock is then generated, through rapid expansion of plasma induced by the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gelatin under tension that results from acoustic impedance mismatching at the bubble wall. We measure the probability of cavitation with varying the bubble radius and the standoff distance. The threshold pressure for the cavitation inception is defined by the probability equal to one half and is predicted, through comparisons to Euler flow simulations, at −25 MPa.

Random lasing from PM597-DCM solutions containing Pt nanoparticles

We, for the first time, report on a new easily fabricated type of PM 597-DCM composites demonstrating random lasing, which can be used as a simple mirror-less laser source. The composites are based on Pt nanoparticles dispersing in PM597-DCM solution. Excitation with green nanosecond laser (532nm) induces random lasing with peaks in the visible spectral range (640nm) and noticeable width of spontaneous emission. The possibility to tune the lasing wavelength of output light with PM597-DCM through photon scattering of Pt nanoparticles is demonstrated.

Cloud cavitation induced by shock-bubble interaction in a viscoelastic solid

We experimentally study a shock-bubble interaction problem in a viscoelastic solid, which is relevant to shock wave lithotripsy. A gas bubble is produced by focusing an infrared laser pulse into gelatin. A spherical shock is then created, through rapid expansion of plasma that results from the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gelatin under tension that results from acoustic impedance mismatching at the bubble wall. Namely, the shock reflects at the bubble interface as a rarefaction wave, which induces the nucleation of cavitation bubbles as a result of rupturing the gelatin.

Ultraviolet vortex generation using periodically bonded β-BaB_2O_4 device

This paper describes the first demonstration of ultraviolet (266nm) vortex generation using the combination of a frequency-doubled nanosecond green laser, a spiral phase plate, and a periodically bonded β-BaB2O4 device. For a laser pumping energy of 9.1 mJ, an ultraviolet vortex energy of 1.24 mJ was obtained, corresponding to a conversion efficiency of 13.7%.

Fast programming metal-gate Si quantum dot nonvolatile memory using green nanosecond laser spike annealing

The ultrafast metal-gate silicon quantum-dot (Si-QD) nonvolatile memory (NVM) with program/erase speed of 1 μs under low operating voltages of ± 7 V is achieved by thin tunneling oxide, in situ Si-QD-embedded dielectrics, and metal gate. Selective source/drain activation by green nanosecond laser spike annealing, due to metal-gate as light-blocking layer, responds to low thermal damage on gate structures and, therefore, suppresses re-crystallization/deformation/diffusion of embedded Si-QDs. Accordingly, it greatly sustains efficient charge trapping/de-trapping in numerous deep charge-trapping sites in discrete Si-QDs. Such a gate nanostructure also ensures excellent endurance and retention in the microsecond-operation Si-QD NVM.

Improving the sidewall quality of nanosecond laser-drilled deep through-silicon vias by incorporating a wet chemical etching process

Through-silicon vias (TSVs) are thought to be the essential process of the next-generation packaging technologies such as three-dimensional integrated circuit, system in package and wafer-level packaging. This Letter investigated the formation quality of deep TSVs using green nanosecond laser drilling process. Moreover, a wet chemical etching (WCE) process was employed to improve the sidewall quality of deep TSVs fabricated using green ns laser pulses. Experimental results show that the TSV sidewall roughness can be markedly reduced, from micrometre to nanometre scale. The proposed method would enable semiconductor manufactures to use ns laser drilling for industrial TSV fabrication as the desired TSV sidewall quality can be achieved by incorporating the WCE process, which is suitable for mass production.

Crystallization processes of amorphous Si by thermal annealing and pulsed laser processing

Amorphous Si thin films deposited on oxidized crystalline Si surface (111) were crystallized by thermal annealing and nanosecond green laser pulses. The Raman scattering spectra show that thermal annealing can provide nearly fully crystallized poly-Si film. Laser crystallization of amorphous Si is more flexible crystallization method, but it is more difficult to reach high levels of crystallinity. Depth studies of laser treated samples reveal a thin amorphous-like interlayer between substrate surface and crystallized Si film.

30 W output of short pulse duration nanosecond green laser generated by a hybrid fiber-bulk MOPA system

We reported a 30 W average output power 532 nm green laser with 5 ns pulsed duration working at 80–100 kHz generated by a hybrid MOPA system. The hybrid MOPA system consisted of a fiber amplifier and two solid-state amplifiers producing 77 W 1064 nm at pulse repetition rates of 80–100 kHz. The IR-to-green optical conversion efficiency was 44.7% at the working point of 100 kHz. The beam quality of green laser was measured better than M 2 < 1.6 in both orthogonal directions. Nanosecond 532 nm lasers with short pulsed duration could be practicable in silicon-based material processing in the Photovoltaic industry.