Effect of hydrogen content on the light induced defect generation in direct current magnetron reactively sputtered hydrogenated amorphous silicon thin films

Abstract

The kinetics of light induced defect generation or the Staebler-Wronski effect have been investigated on device quality hydrogenated amorphous silicon films which were deposited by dc magnetron reactive sputtering. The total hydrogen content (CH) of the films, which varied from ∼10 to 28 at. %, had a strong influence on the defect generation. Low CH (10%-15%) films had a high initial density of defect states (∼7 to 10×1015 cm-3) compared to the high CH (≥17 at. %) films with a density of ∼3×1015 cm -3. However, light exposure increased the defect density more slowly on the low CH films, such that after about 1 h of light exposure their defect density was lower. A high-quality glow discharge produced film was also measured, and behaved similarly to the high CH sputtered films. The greater stability of the low CH films was also reflected in a slower decrease of the electron photoconductivity relative to the other samples. For exposure times (t) up to 1000 h, the total density of defect states of the films increases as a power law: the high CH and glow discharge deposited films follow t0.3 and t0.32, respectively, whereas the low CH film shows t0.23 at long times. The latter behavior is in sharp contrast with previous reports, and indicates that the degradation does not follow the Stutzmann theory or obeys it with a 100× smaller susceptibility to degradation.