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Transfer characteristics of HIZO TFTs subjected to PBS, NBS, LS, NBLS, and PBLS. The upper inset depicts the spectrum of the illumination source on a semilogarithmic scale and the lower inset the schematic cross-section of the TFTs examined. The front- and back-channel interfaces of the TFT are formed by the layers.
The shift in threshold voltage as a function of time during 3 h of bias and light stress followed by 11 h of natural recovery. Stretched-exponential fits to the recovery curves yield the following values of : (, 0.48) for PBS, (, 0.22) for LS, (, 0.21) for NBLS, and (, 0.3) for PBLS. The inset demonstrates that illumination gives rise to a PPC. The OFF-current is .
Transfer characteristics of TFTs subjected to 30 min of illumination at different wavelengths and sampled under light. Inset shows that the PPC becomes more pronounced at shorter wavelengths.
Approximate energy band diagrams of TFT system examined here. Ionized sites are suggested as the origin of the PPC. Negative gate bias bends the energy bands upwards and separates photogenerated e-h pairs.
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