Laser Growth Of Silicon Ribbon

R. W. Gurtler; A. Baghdadi

doi:10.1117/12.958030

24 January 1980 Laser Growth Of Silicon Ribbon

R. W. Gurtler, A. Baghdadi

Proceedings Volume 0198, Laser Applications in Materials Processing; (1980) https://doi.org/10.1117/12.958030
Event: 23rd Annual Technical Symposium, 1979, San Diego, United States

Abstract

Carbon Dioxide and YAG lasers have been used to establish a narrow molten zone in a pre-formed polycrystalline silicon ribbon. To achieve the narrow melt across the width of the ribbon, the laser is focussed and scanned across the ribbon by means of mirror scanners. Large grained "macrocrystalline" silicon ribbon is then drawn from the molten zone at growth rates up to 12.5 cm/min. Photovoltaic cells fabricated on this material have shown conversion efficiencies up to 11.3%. The actual absorbed laser power which is required for ribbon growth of interest, e.g. .15 mm thick, 7.5 cm wide, 7.5 cm/min. growth velocity, is only a few hundred watts. Unfortunately, the reflectivity of liquid silicon at 10.6 μm is very high (>90%) so that multikilowatt CO2 lasers will be needed. Nd:YAG lasers offer about a five-fold improvement in laser coupling to liquid silicon but this advantage is offset by the lower efficiency and higher operating cost of Nd:YAG lasers. The effective laser coupling to the melt can be essentially doubled by using spherical reflectors to re-image the reflected laser beam back onto the molten zone. The emissivity change which occurs upon melting, while disadvantageous for laser power requirements, is a real benefit for melt zone control since this produces an inherent stabilizing effect.

Citation Download Citation

R. W. Gurtler and A. Baghdadi "Laser Growth Of Silicon Ribbon", Proc. SPIE 0198, Laser Applications in Materials Processing, (24 January 1980); https://doi.org/10.1117/12.958030

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KEYWORDS

Silicon

Semiconductor lasers

Carbon dioxide lasers

Liquids

Laser applications

Solids

Mirrors

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