Pulsed Laser Annealing Research Articles

Broad infrared absorption band through ion beam hyperdoping of silicon with selenium

In this work, we present the formation of silicon layers hyperdoped with selenium through Se implantation followed by pulsed laser annealing. The concentration depth distribution of Se atoms was investigated by Rutherford backscattering and X-Ray photoelectron spectroscopies. Scanning tunneling spectroscopy confirmed the formation of intermediate sub-band within Si band gap. The crystallinity of the doped silicon layer and the fraction of Se atoms in Si lattice sites were determined using backscattering yield analysis. Experimental and theoretical sub-band properties were compared and discussed. Notably, a significant increase in light absorption across a wide spectral region (0.2–23.0 μm) was observed, demonstrating the potential of selenium hyperdoping for enhancing infrared absorption in silicon.

Pulsed laser annealed rare earth doped TiO2 thin films for luminescence and sensing applications

Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 °C, proper laser annealing (fluence 50 mJ/cm2, 5–15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under- and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.

Active sites of Te-hyperdoped silicon by hard x-ray photoelectron spectroscopy

Multiple dopant configurations of Te impurities in close vicinity in silicon are investigated using photoelectron spectroscopy, photoelectron diffraction, and Bloch wave calculations. The samples are prepared by ion implantation followed by pulsed laser annealing. The dopant concentration is variable and high above the solubility limit of Te in silicon. The configurations in question are distinguished from isolated Te impurities by a strong chemical core level shift. While Te clusters are found to form only in very small concentrations, multi-Te configurations of type dimer or up to four Te ions surrounding a vacancy are clearly identified. For these configurations, a substitutional site location of Te is found to match the data best in all cases. For isolated Te ions, this matches the expectations. For multi-Te configurations, the results contribute to understanding the exceptional activation of free charge carriers in hyperdoping of chalcogens in silicon.

Laser induced crystallization of sputtered MoS2 thin films

The integration of transition metal dichalcogenides (TMDs) thin films into Si CMOS-based devices requires the development of new bottom-up material growth approaches producing high crystallinity films without affecting the SiO2/Si substrate. For this purpose, sputtering is a suitable deposition method due to its simplicity, jointly with high reliability and large area deposition capabilities. However, sputtered layers are amorphous and require a post-deposition thermal treatment to obtain a highly crystalline film. Nanosecond pulsed laser annealing (PLA) has recently emerged as promising route to achieve large-scale crystalline TMDs films without significantly heating or affecting the underlying substrate. The aim of this work is to explore the possibility to produce crystalline 2H–MoS2 on large areas directly on a SiO2-on-Si substrate. The film structure, composition and morphology were monitored as a function of the laser pulse energy density by Raman spectroscopy, X-rays diffraction, Rutherford backscattered spectroscopy (RBS), scanning transmission electron microscopy (STEM) and atomic force microscopy (AFM). The electrical properties of the film with optimized crystallinity were finally investigated through deposition of Cr/Au contacts using shadow masks. This approach can be scaled to other TMDs materials and substrates, also paving the way for the fabrication of heterostructures and electrical devices on the top of a single substrate.

Rapid laser-induced low temperature crystallization of thermochromic VO2 sol-gel thin films

The thermochromic properties of vanadium dioxide (VO2) offer great advantages for energy-saving smart windows, memory devices, and transistors. However, the crystallization of solution-based thin films at temperatures lower than 400°C remains a challenge. Photonic annealing has recently been exploited to crystallize metal oxides, with minimal thermal damage to the substrate and reduced manufacturing time. Here, VO2 thin films, obtained via a green sol–gel process, were crystallized by pulsed excimer laser annealing. The influence of increasing laser fluence and pulse number on the film properties was systematically studied through optical, structural, morphological, and chemical characterizations. From temperature profile simulations, the temperature rise was confirmed to be confined within the film during the laser pulses, with negligible substrate heating. Threshold laser parameters to induce VO2 crystallization without surface melting were found. With respect to furnace annealing, both the crystallization temperature and the annealing time were substantially reduced, with VO2 crystallization being achieved within only 60 s of laser exposure. The laser processing was performed at room temperature in air, without the need of a controlled atmosphere. The thermochromic properties of the lasered thin films were comparable with the reference furnace-treated samples.

Synthesis of Large-Area Crystalline MoS2 by Sputter Deposition and Pulsed Laser Annealing

The wafer-scale synthesis of layered transitional metal dichalcogenides presenting good crystal quality and homogeneous coverage is a challenge for the development of next-generation electronic devices. This work explores a fairly unconventional growth method based on a two-step process consisting in sputter deposition of stochiometric MoS2 on Si/SiO2 substrates followed by nanosecond UV (248 nm) pulsed laser annealing. Large-scale 2H-MoS2 multi-layer films were successfully synthetized in a N2-rich atmosphere thanks to a fine-tuning of the laser annealing parameters by varying the number of laser pulses and their energy density. The identification of the optimal process led to the success in achieving a (002)-oriented nanocrystalline MoS2 film without performing post-sulfurization. It is noteworthy that the spatial and temporal confinement of laser annealing keeps the Si/SiO2 substrate temperature well below the back-end-of-line temperature limit of Si CMOS technology (770 K). The synthesis method described here can speed up the integration of large-area 2D materials with Si-based devices, paving the way for many important applications.

Nanosecond pulsed laser annealing of Cu/Ag/AZO multilayer thin films for performance improvement and transparent heater application

Nanosecond pulsed laser annealing was performed to improve optical and electrical properties of the Cu/Ag/AZO multilayer films. Different laser fluences (L) and scanning speeds (S) were selected to investigate their influences on optical transparency and electrical conductivity of the films. The results revealed that laser annealing under L = 1.0 J/cm2 and S = 10 mm/s effectively promoted grain growth in the film and caused formation of significantly enlarged particles with a more uniform distribution on the film surface. The as-obtained Cu/Ag/AZO multilayer film possessed the optimal comprehensive property with the highest figure of merit of 3.58 × 10–2 Ω−1, far outperforming the unannealed Cu/Ag/AZO multilayer film (1.92 × 10–2 Ω−1). Subsequently, this film was chosen to fabricate a transparent heater, which exhibited excellent heating performance (saturated temperature: 104.9 ℃; response time: 120 s; applied voltage: 5 V) and heating stability. Its deicing availability was also shown by a deicing test.

SERS active substrates for neonicotinoids studies

Different basic substrates, – Si wafers, (001) SiO2, printer paper, Al2O3, micro-processed (001) SiO2 or diamond abrasive films, have been used to create active Ag and Au nanostructures. In this lecture, we report the use of pulsed-laser deposition and thermal deposition both followed by pulsed-laser annealing; the results are compared. Advanced substrates of Au and Ag on Si were produced in view of surface-enhanced Raman spectroscopy (SERS) detection of the imidacloprid (Nuprid 200 SP) neonicotinoid insecticide in amounts much smaller than those ordinarily applied in agricultural medicine. The SERS peaks intensity rose by at least one order of magnitude after the pulsed-laser annealing of the metal films and nanoparticles arrays formation. The enhancement factor (EF) was estimated to be >5×104, the limit of detection (LOD) reached being < 0.5 nM. The properties of the advanced substrates were compared and discussed. The importance of SERS as a relatively inexpensive and simple method is emphasized in regulating, monitoring and controlling the level of such chemicals as environmental pollutants, thus precluding harming the human and, especially, honey bees’ health.

Enhanced performance in perovskites films by defect engineering and charge carrier transportation via pulsed laser doping of 2D MoS2

High-performance perovskite-based optoelectronic devices require low defect density and efficient charge carrier extraction. In this paper, pulsed laser annealing was combined with two-dimensional MoS2 doping to develop an efficient strategy for the extraction of charge carriers from perovskite films with low defect density. In pulse laser annealing of perovskite films with 2D MoS2 dopant, due to their localized temperature gradients caused by fast laser annealing, the grains are much larger, and the film quality is much better than that of traditional thermal annealing perovskite films. As a result, the films absorb light better. After doping of 2D MoS2, the carrier transport in perovskite films can be increased significantly by passivating Pb-related defects through PbS coordination bonds. Additionally, the shift of the conduction band minimum (CBM) from the perovskite layer to the Au layer provides a well-matched alignment in energy levels between the perovskite and Au layers, which encourages charge carrier extraction. Moreover, the interfacial perovskite lattice moves freely during the annealing and chilling processes due to laser-induced thermomechanical momentum and weak interactions between 2D MoS2 and, thereby reducing the tensile strain in perovskite films. In addition, by improving surface hydrophobicity and relieving residual stresses, perovskite films are more humidity and thermal stable.

Nanosecond Laser Annealing of NMC 811 Cathodes for Enhanced Performance

Improved performance of lithium-ion batteries (LIBs) plays a critical role in the future of next- generation battery applications. Nickel-rich layered oxides such as LiNi0.8Mn0.1Co0.1O2 (NMC 811), are popular cathodes due to their high energy densities. However, they suffer from high surface reactivity, which results in the formation of Li2CO3 passive layer. Herein, we show the role of nanosecond pulsed laser annealing (PLA) in improving the current capacity and cycling stability of LIBs by reducing the carbonate layer, in addition to forming a protective LiF layer and manipulating the NMC 811 microstructures. We use high-power nanosecond laser pulses in a controlled way to create nanostructured surface topography which has a positive impact on the capacity retention and current capacity by providing an increased active surface area, which influences the diffusion kinetics of lithium-ions in the electrode materials during the battery cycling process. Advanced characterizations show that the PLA treatment results in the thinning of the passive Li2CO3 layer, which is formed on as-received NMC811 samples, along with the decomposition of excess polyvinylidene fluoride (PVDF) binder. The high-power laser interacts with the decomposed binder and surface Li+ to form LiF phase, which acts as a protective layer to prevent surface reactive sites from initiating parasitic reactions. As a result, the laser treated cathodes show relative increase of the current capacity of up to 50%, which is consistent with electrochemical measurements of LiB cells.

Effect of Laser Pulse Width and Intensity Distribution on the Crystallographic Characteristics of GeSn Film

Germanium-tin (GeSn) alloy is considered a promising candidate for a Si-based short-wavelength infrared range (SWIR) detector and laser source due to its excellent carrier mobility and bandgap tunability. Pulsed laser annealing (PLA) is one of the preeminent methods for preparing GeSn crystal films with high Sn content. However, current reports have not systematically investigated the effect of different pulse-width lasers on the crystalline quality of GeSn films. In addition, the intensity of the spot follows the gaussian distribution. As a result, various regions would have different crystalline properties. Therefore, in this study, we first provide the Raman spectra of several feature regions in the ablation state for single spot processing with various pulse-width lasers (continuous-wave, nanosecond, femtosecond). Furthermore, the impact of laser pulse width on the crystallization characteristics of GeSn film is explored for different single-spot processing states, particularly the Sn content incorporated into GeSn crystals. The transient heating time of the film surface and the faster non-equilibrium transition of the surface temperature inhibit the segregation of the Sn component. By comparing the Raman spectra of the pulsed laser, the continuous-wave laser shows the most acute Sn segregation phenomenon, with the lowest Sn content of approximately 2%. However, the femtosecond laser both ensures crystallization of the film and effective suppression of Sn expulsion from the lattices, and the content of Sn is 8.07%, which is similar to the origin of GeSn film.

Thermally stimulated exo-electron emission and desorption from Lu2O3:Eu3+ surfaces

Thermally stimulated exo-electron emission (TSEE) and thermally stimulated desorption (TSD) methods were employed to characterize interactions in the surface of thin films of Lu2O3 doped by Eu3+ fabricated by pulsed laser deposition. Samples with 1 and 3% doped europium were selected. Pulsed laser annealing (PLA) was performed to modify surfaces. TSEE maxima are shown at temperature ranges T ∼120, 270 °C and T ∼250, 350 °C for 1 and 3% europium content, respectively. The TSEE maxima correspond with TSD maxima of LuO and EuO observed at higher temperatures. At lower temperatures the release of atomic oxygen Oat and OH radicals is taking place at the points, edges, and other imperfections of the crystals. The presence of Eu3+ contributes to the incipient material decomposition in dependence on Eu concentration. Desorption of individual atoms and radicals (Oat, OH, Lu, Eu, LuO, and EuO) during decomposition into components reveals a coincidence with the emission of negative ions. This can be explained by the fact that electrons are simultaneously emitted when particles are released. Activation energy and frequency factors were calculated to precise description of the surface processes.

Highly Stable Electrochemical Supercapacitor Performance of Self-Assembled Ferromagnetic Q-Carbon.

Novel phase Q-carbon thin films exhibit some intriguing features and have been explored for various potential applications. Herein, we report the growth of different Q-carbon structures (i.e., filaments, clusters, and microdots) by varying the laser energy density from 0.5 to 1.0 J/cm2 during pulsed laser annealing of amorphous diamond-like carbon films with different sp3-sp2 carbon compositions. These unique nano- and microstructures of Q-carbon demonstrate exceptionally stable electrochemical performance by cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy for energy applications. The temperature-dependent magnetic studies (magnetization vs magnetic field and temperature) reveal the ferromagnetic nature of the Q-carbon microdots. The saturation magnetization and coercive field values decrease from 132 to 14 emu/cc and 155 to 92 Oe by increasing the temperature from 2 to 300 K, respectively. The electrochemical performances of Q-carbon filament, cluster, and microdot thin-film supercapacitors were investigated by two-electrode configurations, and the highest areal specific capacitance of ∼156 mF/cm2 was observed at a current density of 0.15 mA/cm2 in the Q-carbon microdot thin film. The Q-carbon microdot electrodes demonstrate an exceptional capacitance retention performance of ∼97.2% and Coulombic efficiency of ∼96.5% after 3000 cycles due to their expectational reversibility in the charging-discharging process. The kinetic feature of the ion diffusion associated with the charge storage property is also investigated, and small changes in equivalent series resistance of ∼9.5% and contact resistance of ∼9.1% confirm outstanding stability with active charge kinetics during the stability test. A high areal power density of ∼5.84 W/cm2 was obtained at an areal energy density of ∼0.058 W h/cm2 for the Q-carbon microdot structure. The theoretical quantum capacitance was obtained at ∼400 mF/cm2 by density functional theory calculation, which gives an idea about the overall capacitance value. The obtained areal specific capacitance, power density, and impressive long-term cyclic stability of Q-carbon thin-film microdot electrodes endorse substantial promise in high-performance supercapacitor applications.

An Emerging Local Annealing Method for Simultaneous Crystallization and Activation in Xtacking 3-D NAND Flash

The high thermal budget of three-dimensional NAND Flash (3D NAND Flash) is the key issue limiting the increase in vertical integration. The main purpose of this article is to design a local and high temperature annealing function to reduce the thermal budget and gain a high activation rate without diffusion at a target depth to improve the performance of 3D NAND Flash devices by laser annealing with green wavelength. The method of nanosecond pulse laser annealing (ns-PLA) for amorphous silicon (a-Si) crystallization and activation has been proven, and this method has the benefits of a low thermal budget and controllable heating. According to previous experiments, one of the important results is that ns-PLA with high energy can provide a high temperature that reaches the melting point of a-Si and obtain a deep and monocrystal-like silicon channel through liquid phase crystallization in 3D NAND applications and obtain a higher activation rate. These results cast emerging light on low thermal budget processes based on ns-PLA in 3D NAND flash for future architecture such as Xtacking architecture, and have significant ramifications for impurity activation rates and reducing channel leakages.

The Impact of Side-Selective Laser Tailoring of Titania Nanotubes on Changes in Photoelectrocatalytic Activity

Over the last few decades, titanium(IV) oxide-based materials have gained particular attention due to their stability, corrosion resistance, photocatalytic activity under UV light, and possibilities for modification. Among various structures, TiO2 nanotubes (NTs) grown on Ti foil or glass substrates and obtained through a simple anodization process are widely used as photocatalysts or photoanodes. During the anodization process, the geometry of the nanotubes (length, distribution, diameter, wall thickness, etc.) is easily controlled, though the obtained samples are amorphous. Heat treatment is required to transform the amorphous material into crystalline material. However, instead of time- and cost-consuming furnace treatment, fast and precise laser annealing is applied as a promising alternative. Nonetheless, laser treatment can result in geometry changes of TiO2 NTs, consequently altering, their electrochemical activity. Moreover, modification of the TiO2 NTs surfaces with transition metals and further laser treatment can result in materials with unique photoelectrochemical properties. In this regard, we gathered the latest achievements in the field of laser-treated titania for this review paper. We mainly focused on single structural and morphological changes resulting from pulsed laser annealing and their influence on the electrochemical properties of titania. Finally, the theoretical basis for and combination of laser- and metal-modifications and their impact on the resulting possibilities for electrochemical water splitting are also discussed.

Microstructure and defect engineering of graphite anodes by pulsed laser annealing for enhanced performance of lithium-ion batteries

Nanosecond pulsed laser annealing significantly improves cyclability and current carrying capacity of lithium-ion batteries (LIBs). This improvement is achieved by engineering of microstructure and defect contents present in graphite in a controlled way by using pulsed laser annealing (PLA) to increase the number density of Li+ ion trapping sites. The PLA treatment causes the following changes: (1) creates surface steps and grooves between the grains to improve Li+ ion charging and intercalation rates; (2) removes inactive polyvinylidene difluoride (PVDF) binder from the top of graphite grains and between the grains which otherwise tends to block the Li+ migration; and (3) produces carbon vacancies in (0001) planes which can provide Li+ charging sites. From X-ray diffraction data, we find upshift in diffraction peak or reduction in planar spacing, from which vacancy concentration was estimated to be about 1.0%, which is higher than the thermodynamic equilibrium concentration of vacancies. The laser treatment creates single and multiple C vacancies which provide sites for Li+ ions, and it also produces steps and grooves for Li+ ions to enter the intercalating sites. It is envisaged that the formation of these sites enhances Li+ ion absorption during charge and discharge cycles. The current capacity increases from an average 360 mAh/g to 430 mAh/g, and C–V shows significant reduction in SEI layer formation after the laser treatment. If the vacancy concentration is too high and charge-discharge cycles are long, then trapping of electrons by Li+ may occur, which can lead to Li0 formation and Li plating causing reduction in current capacity.

Creation of GaMnAs ferromagnetic semiconductor by combined laser method

GaMnAs layers made by pulsed laser deposition in vacuum on semi-insulating GaAs substrates have been studied. During the creation of the structures, the substrate temperature varied in the range from 200 to 350oC, and the thickness of the layers was ~ 50 nm. Samples of the manufactured structures were annealed by pulses of an excimer KrF-laser. The analysis of the Raman scattering spectra of annealed samples using their approximation by Lorentz functions showed, in addition to peaks in the LO- and TO-GaAs modes, the presence of a coupled phonon-plasmon mode. As a result of annealing, a significant increase in the hole conductivity of the layers is observed (the resistance decreases from Rs~107-109 Ω to Rs~ 900-3000 Ω). The type of magnetic field dependence of magnetization at room temperature changes significantly: there is a transition from a nonlinear characteristic with a hysteresis loop for the initial sample (appearing due to the presence of MnAs compound inclusions with a Curie temperature above room temperature) to a linear behavior for the annealed sample. The study of galvanomagnetic properties at temperatures from 10 to 150 K shows the existence of ferromagnetism in GaMnAs layers with a Curie temperature reaching 90 K. The observed effects allow us to conclude that the applied pulsed laser action leads to modification (dissolution) of MnAs inclusions, electrical activation of Mn and, as a consequence, to the formation of a single-phase ferromagnetic semiconductor GaMnAs. Keywords:: pulsed laser deposition, pulsed laser annealing, ferromagnetic semiconductor.

Multiscale Simulations for Defect-Controlled Processing of Group IV Materials

Multiscale approaches for the simulation of materials processing are becoming essential to the industrialization of future nanotechnologies, as they allow for a reduction in production costs and an enhancement of devices and applications. Their integration as modules of “digital twins”, i.e., a combined sequence of predictive chemical–physical simulations and trained black-box techniques, should ideally complement the real sequence of processes throughout all development and production stages, starting from the growth of materials, their functional manipulation and finally their integration in nano-devices. To achieve this framework, computational implementations at different space and time scales are necessary, ranging from the atomistic to the macro-scale. In this paper, we propose a general paradigm for the industrially driven computational modeling of materials by deploying a multiscale methodology based on physical–chemical simulations bridging macro, meso and atomic scale. We demonstrate its general applicability by studying two completely different processing examples, i.e., the growth of group IV crystals through physical vapor deposition and their thermal treatment through pulsed laser annealing. We indicate the suitable formalisms, as well as the advantages and critical issues associated with each scale, and show how numerical methods for the solution of the models could be coupled to achieve a complete and effective virtualization of the process. By connecting the process parameters to atomic scale modifications such as lattice defects or faceting, we highlight how a digital twin module can gain intrinsic predictivity far from the pre-assessed training conditions of black-box “Virtual Metrology” techniques.

Non-Equilibrium Growth of Surface Wrinkles Emerging in an SiO2/Si Stack during Si Melting Induced by UV Nanosecond Pulsed Laser Annealing

UV nanosecond pulsed laser annealing (UV-NLA) is demonstrating clear benefits in the emerging 3D-integrated electronic devices, where the allowed thermal budget is strictly limited to preserve underlying device performance. A possible drawback of UV-NLA is that melting a solid substrate covered by a dielectric layer, which can be found in typical CMOS device structures, induces wrinkles on the surface and may be an issue for subsequent processes. In this study, UV-NLA is performed in thermally-grown SiO2/Si structures to systematically investigate the formation of wrinkles. A classical analytical model adopted from literature shows a good agreement with our experimental results if a fitting coefficient is involved. Interestingly, its value is rapidly increasing for a thinner (roughly less than 50 nm) SiO2 film, whereas it becomes closer to unity for a thicker (roughly greater than 50 nm) SiO2 film. This might infer a possible discrepancy of the material properties taken from literature and those of real industrial thin SiO2 films. The impact of the as-grown SiO2 film stress on the growth of wrinkles is also investigated, improving the statistics of the measurements. The results do not show any significant impact possibly because of the degree of the as-grown SiO2 film stress being negligible compared to the SiO2 shear modulus.

Effect of pulsed laser annealing on the properties of (Ga,Mn)As layers

• Ferromagnetic (Ga,Mn)As layers were obtained by pulsed laser deposition and annealing. • Results of X-ray diffraction, TEM and the magnetization study are presented. • Decomposition of MnAs inclusions is observed after laser annealing of thin (Ga,Mn)As layer. • The Curie temperature increased to 105–110 K in the annealed thin (Ga,Mn)As layer. We have investigated the layers of the (Ga,Mn)As diluted magnetic semiconductor with the thickness in the range of 150 – 400 nm, which have been formed by the combination of the methods of a pulsed laser deposition and a post-growth pulsed laser annealing. It has been found that the laser annealing has a significant effect on the structural, magnetic, and electrical properties of the thinnest (∼150 nm) (Ga,Mn)As layer. For this layer the additional activation of the Mn impurity, the Curie temperature increase and the dissolution of the second phase MnAs clusters have been observed. The results of model calculations of heat spread in (Ga,Mn)As layer have shown that in thicker layers a MnAs melting point temperature is not achievable (for the chosen conditions of pulsed laser annealing) in the entire layer.