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 deposited on glass substrates at 250°C by combining rf glow discharge decomposition of silane-helium gas mixtures and ultraviolet laser irradiation on the surface of the growing film. The effect of the laser fluence on the optical and electrical properties of the films was investigated with combined in situ ellipsometry and ex situ techniques. Particular attention was paid to the properties of the films deposited at low and high laser fluences. At a low laser fluence, the resulting hydrogenated amorphous silicon films display a reduced defect density as compared to unirradiated ones. At laser fluences above the melting threshold, we obtain microcrystalline silicon films with a high surface roughness, as observed by scanning electron microscopy, and high electron mobility, as deduced from time resolved microwave conductivity measurements. The enhanced optical absorption produced by the roughness along with the high electron mobility make these films excellent candidates for photodetection and photovoltaic devices.