Characterization of reactively magnetron sputtered hydrogenated amorphous silicon films

This work gives the results of a systematic study of the infrared absorption and photoelectric conductivity of hydrogenated amorphous silicon (a-Si:H) prepared by rf planar magnetron sputtering. The substrate temperature TS was varied between 300 and 700 K and the hydrogen partial pressure during the sputtering process between pH=1×10−4 and 1×10−3 Torr, the argon pressure was kept constant at 2.5×10−3 Torr. Characteristic changes in the hydrogen bonding configuration and in the electrical conductivity were observed. A sufficiently passivated and chemical homogeneous a-Si:H material which contains an amount of 10–15 at. % hydrogen mainly in dispersed SiH bonding configurations, could be obtained at elevated substrate temperatures between 500 and 600 K and an adequate hydrogen partial pressure. The AM1 photoconductivity σph(AM1) reaches values around 10−4 (Ω cm)−1. The ratio of the photoconductivity to the dark conductivity σph(AM1)/σD, which served as a measure for the quality of the films, was 104 to 105 at TS=590 K and corresponded to a minimum value of the density of states near the midgap of the films. At lower substrate temperatures a rather inhomogeneous material grew with high hydrogen content. Both the photoconductivity and dark conductivity were very low. At temperatures above 600 K hydrogen clustering at inner surfaces occurred and the photoconductivity decreased by several orders of magnitude.