Luminescence studies of plasma-deposited hydrogenated silicon

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Abstract
The photoluminescence of plasma-deposited amorphous silicon is investigated. The luminescence intensity and spectral line shape are shown to be sensitive to many deposition variables, in particular the power coupled into the discharge, the concentration of silane in the gas stream, and the deposition substrate temperature. Maximum intensity is obtained in samples deposited with low power (∼1 W), a silane concentration of ≳ 10% and a deposition temperature of 200-300°C. ESR studies show that the luminescence intensity is determined by competing nonradiative transitions to localized defect states whose density varies with deposition conditions. The presence of defect states is related to the way hydrogen is incorporated into the samples, but the details of the defect structure are not yet clear. Oxygen impurities are observed to give a broad, weak luminescence peak centered near 1.1 eV. It is suggested that the active oxygen centers are similar to the charged defects postulated for chalcogenide glasses.