METASTABLE CHANGES IN A-SI-H A-SI,N-H THIN-FILM TRANSISTORS BY LIGHT ILLUMINATION/

Metastable changes in a-Si:H/a-Si,N:H thin film transistors (TFTs) cau sed by strong light illumination are studied by measurements of transf er characteristics and constant photocurrent method (CPM). We employed CPM method, for the first time, to monitor the change of light-induce d defect density of a-Si:H in TFT structure. We found a pronounced pos itive and a temporal negative shift of flat-band voltage due to a ligh t illumination. From this, we conclude that charge trapping and detrap ping also can occur dominantly in a-Si:Hla-Si,N:H TFTs under high inte nsity light illumination. The light-induced defect density is calculat ed from the measured CPM absorption spectrum, and it increases with il lumination time according to the stretched exponential function, as in the case of Staebler-Wronski effect.