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.
This paper presents the comparison among different nonlinear seismic analysis methods applied to masonry buildings, i.e. pushover analyses with invariant lateral force distributions, adaptive pushover analysis and nonlinear dynamic analysis. The study focuses on the influence of lateral force distribution on the results of the pushover analysis. Two simple benchmark case studies are considered for the purpose of the research, i.e. a four-wall masonry building prototype without floor rigid diaphragms and a two-wall system with a cross-vault. The comparative study offers a useful review of pushover analysis methods for masonry structures and shows advantages and possible limitations of each approach.
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.
Flash lamp annealing (FLA), a rapid annealing technique with a millisecond-order duration, can form polycrystalline silicon (poly-Si) films of a few µm thickness on glass substrates by crystallizing precursor amorphous Si (a-Si) films without serious thermal damage to the substrates. We attempt to use several kinds of metal films for adhesion layers inserted between the Si films and the glass substrates to prevent Si film peeling during FLA. One of the requirements for the insertion metals is a melting point (T
melt) higher than 1414 °C, to which the metal films could be heated during the crystallization induced by FLA. Of the metal films attempted, only Cr films can prevent Si film peeling from soda lime glass substrates, which have a much larger thermal expansion coefficient than quartz, indicating the necessity of sufficient adhesiveness to glass and Si as well as of a high T
melt. Actual solar cell operation is demonstrated using a flash-lamp-crystallized poly-Si film as an absorber layer and a Cr film as a back electrode.
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