OPTICAL AND TRANSPORT-PROPERTIES OF AMORPHOUS AND MICROCRYSTALLINE SILICON FILMS PREPARED BY EXCIMER-LASER ASSISTED RF GLOW-DISCHARGE DEPOSITION

Hydrogenated amorphous and microcrystalline silicon films were deposit ed on glass substrates at 250 degrees C by combining rf glow discharge decomposition of silane-helium gas mixtures and ultraviolet laser irr adiation on the surface of the growing film. The effect of the laser f luence on the optical and electrical properties of the films was inves tigated with combined in situ ellipsometry and ex situ techniques. Par ticular attention was paid to the properties of the films deposited at low and high laser fluences. At a low laser fluence, the resulting hy drogenated amorphous silicon films display a reduced defect density as compared to unirradiated ones. At laser fluences above the melting th reshold, we obtain microcrystalline silicon films with a high surface roughness, as observed by scanning electron microscopy, and high elect ron mobility, as deduced from time resolved microwave conductivity mea surements. The enhanced optical absorption produced by the roughness a long with the high electron mobility make these films excellent candid ates for photodetection and photovoltaic devices. (C) 1998 American Va cuum Society.