A study was made of the defect density and disorder in hydrogenated amorphous Si-C alloys produced by rf glow discharge of silane-methane-H mixtures, by combining spectroscopic ellipsometry and photothermal deflection spectroscopy measurements. Increasing the methane flow rate led to a widening of the optical gap and to an increase in the apparent disorder, deduced from the standard analysis of the exponential absorption edge (the so-called Urbach energy). The sub-gap absorption decreased with increasing methane flow-rate. This indicated a lower density of defects with increasing C content, and contrasted with the increased disorder. This apparent contradiction resulted from the presence of 3 absorption bands within the gap of this material, and which rendered unreliable the standard analysis of the disorder in Si C alloys.

Optical Study of Disorder and Defects in Hydrogenated Amorphous Silicon Carbon Alloys. T.Nguyen-Tran, V.Suendo, P.Roca i Cabarrocas: Applied Physics Letters, 2005, 87[1], 011903 (3pp)