We investigate the microstructure of polycrystalline silicon films (grain size, texture and grain boundary population) on glass substrates. These films are produced from amorphous silicon precursor layers and crystallized by-scanning the raw beam of a continuous wave Ar~+- ion laser operated at a wavelength of 514 nm over the amorphous silicon. In thin film solar cells, laser crystallized films might be used as seeding layers for a subsequent epitaxial thickening process to increase the film thickness to account for sufficient light absorption. The defect density produced by the most promising low-temperature epitaxy processes shows a minimum for (001) oriented substrates. Transmission electron microscopy together with electron back-scattering diffraction analysis of the crystallized layers reveal grain widths of about 10 μm and grain lenghts of several 10 μm. Under certain processing conditions a preferred (001)-surface normal orientation (texture) forms. This preferred surface normal could substantially increase the quality of epitaxial layers grown on laser-crystallized films. The grain boundary population is dominated in the textured films by coincidence boundaries, essentially twin boundaries of first and second order as well as Σ = 5 boundaries.
展开▼
