Understanding the dynamics of the laser crystallization (LC) process of Ge thin films by nanosecond (ns) pulsed infrared (IR) lasers is important for producing homogeneous, crack-free crystalline device-grade films for use in thin-film transistors, photo-detectors, particle detectors, and photovoltaic applications. Our motivation is to describe a ns IR laser-based crystallization process of Ge by implementing suitable parameters to fabricate thin-film devices. Our LC technique was applied to crystallize thin amorphous Ge (a-Ge) films with thicknesses suitable for device applications. The LC process was applied to a 300 nm-thick a-Ge thin film utilizing a 200 ns pulsed IR laser with a wavelength of 1064 nm. Electron-beam-evaporation-deposited a-Ge on glass substrates were subject to successive ns laser pulses with a line focus. The crystallinity of the polycrystalline Ge (pc-Ge) films was evaluated by Raman spectroscopy, optical microscopy, and electron backscatter diffraction (EBSD). LC-Ge exhibited a Raman peak of around 300 cm–1, confirming successful crystallization of a-Ge. pc-Ge domain sizes exceeding several tens of micrometers were observed in EBSD scans. LC of a-Ge minimizes the thermal energy budget of processing and provides flexibility to locally crystallize the film. Our work is the first demonstration of the LC of a-Ge thin films, resulting in domain sizes exceeding tens of micrometers via a ns pulsed IR laser.

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The laser crystallization (LC) of amorphous silicon thin films into polycrystalline silicon (pc-Si) thin films on glass substrates is an active field of research in the fabrication of Si-based thin film transistors and thin film solar cells. Efforts have been, in particular, focused on the improvement of LC technique. Adhesion promoters of the crystallized Si thin films at the glass interface play a crucial role in the stability and device performance of fabricated structures. The crystalline Si thin films are required to be produced free of contamination risks arising from impurity diffusion from the glass substrate. Moreover, it is preferable to fabricate pc-Si thin films at temperatures as close as possible to the ambient temperature for an effective cost reduction. In this work, we demonstrate the successful use of a commercially available nanosecond pulsed laser marker at 1064 nm wavelength for Si crystallization at ambient conditions compared to the common method of pre-elevated substrate temperatures used in continuous wave laser irradiation technique. As a result, our technique results in a better energy balance than that in previous works. The second main purpose of this study is to enhance the crystallinity of Si thin films and to determine the best choice of an intermediate dielectric layer (IDL) comparatively among four thin buffer layers, namely, SiN x , SiO 2 , ZnO, and TiO 2 , for the sake of obtaining improved adhesion and larger crystalline domains as compared to that on a direct Si–glass interface. The crystalline qualities of samples containing IDLs of SiN x , SiO 2 , ZnO, and TiO 2 were compared via Raman spectroscopy analysis and electron backscatter diffraction method against the direct Si–glass interface reference. The analyses quantitatively showed that both the crystallinity and the domain sizes can be increased via IDLs.

Pulsed laser absorption-mediated explosive crystallization of silicon films has extensively been studied using microscopy techniques on single laser pulse-irradiated regions in the literature. In this work, we experimentally demonstrate and theoretically explain in detail the use of slow quenching regime for laser crystallization mediated by highly overlapping pulses. Increasing the use of Si in thin film transistors and photovoltaic applications drives researchers to find cost-effective and efficient ways of manufacturing crystalline Si films on various types of substrates. Understanding the mechanism of the laser crystallization process of Si films by pulsed lasers becomes crucial. This work reveals the laser crystallization mechanism of Si thin films in macroscopic scales by considering heat transfer and accumulation dynamics. Our motivation is to describe the dynamics of the laser crystallization of Si films to provide a complementary guide for the production of device-grade c-Si films by infrared pulsed laser without employing preheated substrates. c-Si grains exceeding 2 mm in size were formed by laser crystallization of 1 μm-thick Si films without any pre/ postannealing step at room temperature and within a typical continuous wave irradiation-based light energy budget, which we think to be the most important achievement of our work.

Interest in laser crystallization (LC) of silicon (Si) thin films has been on the rise in fabrication of polycrystalline silicon (pc-Si) based thin/ultrathin photovoltaic solar cells and Si based thin film transistors (TFT). Laser based fabrication of device quality pc-Si thin films at room temperature is expected to be a key enabling technology because of its low energy, material and process time budget. Fabrication of high-quality pc-Si thin films without pre-/post-treatment at large is a disruptive technology which has the potential to revolutionize the Si thin film industry. We hereby describe in detail a multi-wavelength laser processing platform specially developed for crystallization of amorphous silicon (a-Si) thin films into pc-Si thin films. The platform has three main stages. The first stage consists of a nanosecond pulsed ytterbium (Yt 3+ ) doped fibre-laser with a master oscillator power amplifier architecture, operating at a wavelength of 1064 nm with an adjustable repetition rate between 80 kHz-300 kHz. The output beam has a maximum power of 18 W with a pulse energy of 90 µJ. The pulse durations can be set to values between 15 ns-40 ns. The second stage has free-space optical elements for second harmonic generation (SHG) which produces an emission at a wavelength of 532 nm. Conversion efficiency of the SHG is 25% with an output pulse energy of 20 µJ. The platform provides two wavelengths at either 1064 nm or 532 nm in crystallization of a-Si films for different crystallization regimes. The last stage of the platform has a sample processing assembly with a line-focus, which has an x-y motorized stage on a vibration isolated table. Speed of the motorized stage can be set between 1 mm/s-100 mm/s. Stage speed and repetition rate adjustments help to adjust overlap of successive pulses between 97.22-99.99%. Our platform has variety of tune parameters that make it a uniquely flexible system for delicate Si thin film crystallization. A large selection of operational parameter combinations, the wavelength selection and simultaneous x-y scanning capability allow users to crystallize Si films on various substrates optimally. The operation wavelength choice can be done by considering optical absorption and thickness of a-Si films on different types of substrates. Hence, delivering precise amount of absorbed energy in the line-focus irradiation is useful in increasing the average size of crystalline domains; moreover, nucleation of crystallites can be initiated either from the top or bottom interface of the film. Continuous and simultaneous motion of the stage in two dimensions allows to process arbitrary continuous pc-Si geometries in a-Si film. In summary, our multi-wavelength laser processing platform offers all-in-one LC utility for intricate LC-Si processing.