Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates. The EC starts from the edges of the a-Si films due to additional heating from flash lamp light. This is followed by lateral crystallization with a velocity on the order of m/s, leaving behind periodic microstructures in which regions containing several hundreds of nm-ordered grains and regions consisting of only 10-nm-sized fine grains alternatively appear. The formation of the dense grains can be understood as explosive solid-phase nucleation, whereas the several hundreds of nanometer-sized grains, stretched in the lateral direction, are probably formed through explosive liquid-phase epitaxy. This phenomenon will be applied to the high-throughput formation of thick poly-Si films for solar cells.

Polycrystalline silicon (poly-Si) films as thick as 4.5 mm are prepared by flash lamp annealing (FLA) of amorphous silicon (a-Si) films without thermal damage onto glass substrates. The a-Si films are deposited by catalytic chemical vapor deposition (Cat-CVD) at 320 C. Since the hydrogen content in Cat-CVD a-Si films is as low as 3 at. %, they are easily converted to poly-Si without any dehydrogenation treatment. Chromium (Cr) films 60 nm thick are coated onto glass substrates to achieve high area uniformity of poly-Si formation. Secondary ion mass spectroscopy (SIMS) reveals that no diffused Cr atoms are detected inside poly-Si films and that crystallization is not the well-known metal-induced crystallization. Raman spectra from the poly-Si films show high crystallinity close to 1, and the photoluminescence (PL) spectrum demonstrates clear band-to-band transition, indicating the formation of device-quality poly-Si by FLA of Cat-CVD a-Si.

We have succeeded in forming polycrystalline silicon (poly-Si) films with thicknesses of over 4 mm on soda lime glass by flash lamp annealing (FLA) of precursor amorphous Si (a-Si) films deposited by catalytic chemical vapor deposition (Cat-CVD). The insertion of Cr thin films between glass substrates and a-Si significantly improves the adhesion of Si films to the glass substrates, resulting in uniform crystallization of a-Si in 20 Â 20 mm 2 area. Several types of substrate, such as quartz substrates, are also used instead of soda lime glass to elucidate the effects of the properties of glass substrates on formation of the poly-Si films. a-Si films tend to be crystallized under lower irradiance than those on quartz glass substrates, which can be described by the lower thermal conductivity and the thermal diffusion length of soda lime glass. Raman spectra of the poly-Si films on soda lime glass show high crystallinity close to unity. The utilization of soda lime glass with poor thermal resistivity is of great importance for the cost-effective mass production of thin-film poly-Si solar cells.

Current interatomic potentials for compound semiconductors, such as GaAs, fail to correctly predict the ab initio calculated and experimentally observed surface reconstructions. These potentials do not address the electron occupancies of dangling bonds associated with surface atoms and their well established role in the formation of low-energy surfaces. The electron counting rule helps account for the electron distribution among covalent and dangling bonds, which, when applied to GaAs surfaces, requires the arsenic dangling bonds to be fully occupied and the gallium dangling bonds to be empty. A simple method for linking this electron counting constraint with interatomic potentials is proposed and used to investigate energetics of the atomic scale structures of the GaAs(001) surface using molecular statics methods.

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