DC versus pulse-type negative bias stress effects on the instability of amorphous ingazno transistors under light illumination

We report that a pulsed negative bias stress slightly deteriorates the photoelectric stability of amorphous InGaZnO thin-film transistors, whereas a dc negative bias stress induces a large threshold voltage shift under the light. In the case of pulsed bias stresses, many of photoexcited positive charges might be recombined during the interval between pulses while those charges under dc bias drift to the channel interface without recombination. Interfacial trap density measurements explain the effects of such photoexcited positive charges on the interface.