Interface Passivation in Amorphous Silicon TFTs by Various Gate Dielectric Materials

We have used photothermal deflection spectroscopy to examine deep gap absorption in amorphous silicon films deposited on silicon oxide and silicon nitride. Variations in the interface state density deduced from PDS correlate well with the performance characteristics of thin-film transistors. We have demonstrated processes which degrade the interfacial abruptness also increase the interface state density. In transistors this leads to a degradation in device stability. We found devices with oxide gates to be more stable and show lower interface state density than devices with nitride gates for a specific set of deposition conditions. The correspondence between deep gap absorption and transistor characteristics shows that PDS is a valuable technique for characterizing and optimizing fabrication processes.