We propose a new method to estimate the explosive crystallization (EC) velocity (v EC ) of amorphous silicon (a-Si) films using multi-pulse flash lamp annealing (FLA). This system produces discrete pulses at frequencies of 1-10 kHz to form a quasi-millisecond pulse. The multi-pulses leave behind macroscopic stripe patterns on the surfaces of polycrystalline Si (poly-Si) films, the widths of which are indications of v EC . We find that catalytic chemical-vapor-deposited (Cat-CVD) and sputtered a-Si films show v EC of $4 m/s, whereas the use of electron-beam-evaporated a-Si results in much higher v EC of $14 m/s, indicating the emergence of different EC mechanisms.Rapid annealing using sub-second pulse light is of great importance as the methods of crystallizing precursor amorphous silicon (a-Si) films to form device-quality polycrystalline Si (poly-Si) films because of the availability of low-cost glass or plastic substrates. [1][2][3][4][5][6][7][8] This non-thermal equilibrium sub-second annealing sometimes induces explosive crystallization (EC), high-speed lateral crystallization driven by the release of latent heat. 9-15 It has been know that the EC of a-Si occurs in liquid-phase and/or in solid-phase, which results in different EC velocity (v EC ). 9-13 In-situ observation of EC, however, is not easy because of enormously high v EC on the order of m/s. Although v EC of a-Si films has been experimentally estimated by some of in-situ or ex-situ methods, 9,14 they require complicated experimental system or expensive equipments.We have so far found that flash lamp annealing (FLA), millisecond-order annealing using Xe lamps, can induce EC of a few m-thick a-Si films and the EC observed is based on solid-phase nucleation (SPN) and partial liquid-phase epitaxy (LPE), 16 unlike previously reported results that have shown the clear evidences of EC through simple LPE. 9 The v EC of Si films in the case of FLA, however, has not been evaluated, because of the difficulty of using an additional measurement system in a FLA system that has a character of large-area pulse emission. The purpose of this study is to utilize a quasi-millisecond multi-pulse FLA system, instead of conventional single millisecond-pulse FLA, in order to estimate the v EC of Si films from signatures left on poly-Si films formed due to multi-pulse emission which induces temperature modulation of Si during millisecond treatment. The determination of v EC can contributes to understand the mechanism of EC.We first formed 60-nm-thick Cr films on 20 Â 20 Â 0.7 mm 3 -sized quartz substrates by sputtering in order to suppress Si film peeling during FLA. 17 We then prepared 2-4 m-thick a-Si films formed by catalytic chemical vapor deposition (Cat-CVD), sputtering, and electron-beam (EB) evaporation on Cr-coated quartz glass substrates, the detailed deposition conditions of which are summarized in Table I. FLA system used in this study, produced by Design System Co., Ltd., can supply a quasi-millisecond pulse consisting of discrete sub-pulses emitted at variabl...

Flash lamp annealing (FLA) with millisecond-order pulse duration can crystallize microm-order-thick a-Si films on glass substrates through explosive crystallization (EC), and flash-lamp-crystallized (FLC) poly-Si films consist of densely-packed nanometer-sized fine grains. We investigate the impact of the hydrogen concentration and the defect density of precursor a-Si films on crystallization mechanism and the microstructures of FLC poly-Si films, by comparing chemical-vapor-deposited (CVD) and sputtered precursor a-Si films. Transmission electron microscopy (TEM) observation reveals that FLC poly-Si films with similar periodic microstructures are formed by the FLA of the two kinds of precursor films, meaning no significant influence of hydrogen atoms and defect density on crystallization mechanism. This high flexibility of the properties of precursor a-Si films would contribute to a wide process window to reproducibly form FLC poly-Si films with the particular periodic microstructures.

We perform transmission electron microscopy investigation of the microstructures of polycrystalline silicon (poly-Si) films formed through explosive crystallization (EC) induced by flash lamp annealing (FLA) of precursor amorphous silicon (a-Si) films. Two characteristic regions, formed periodically as a result of EC, show different microstructures: one consists of randomly oriented, densely packed fine grains of approximately 10 nm in size, whereas the other has relatively large (>100 nm), stretched grains, probably formed through liquid-phase epitaxy onto solid-phase-nucleated grains. Little a-Si tissue surrounding grains can be observed in the lattice images of flash-lamp-crystallized poly-Si films, which would be favorable for the rapid transport of photocarriers.

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We have investigated carrier transport properties of µm-order-thick polycrystalline silicon (poly-Si) films formed by flash lamp annealing (FLA) of precursor amorphous Si (a-Si) films on glass substrates. The Hall mobility of flashlamp-crystallized (FLC) poly-Si films decreases as doping concentration increases, and then reversely increase with further increase in doping concentration, both in the cases of p-and n-type poly-Si films. The tendency observed is characteristic of poly-Si materials having a number of grain boundaries at which carriers are trapped. N2-atmosphere furnace annealing of FLC poly-Si films with low doping concentration significantly recovers their carrier concentration and improve their carrier mobility up to more than 10 cm 2 /Vs, which is probably because of the termination of the trapping states by hydrogen (H) atoms that exists in FLC poly-Si films on the order of 10 21 /cm 3 . The realized mobility of FLC poly-Si films exceeds those of conventional chemical-vapor-deposited (CVD) microcrystalline Si (µc-Si) films, and the remarkable carrier transport properties would lead to effective carrier collection and resulting high quantum efficiency of FLC poly-Si solar cells.