Abstract-In this work, low temperature fabrication of an amorphous InGaZnO thin film transistor (a-IGZO TFT) was demonstrated. The maximum process temperature was 200 °C. The gate dielectric was a sol-gel SiO 2 film while the channel layer was a sputtered a-IGZO semiconductor. The optimal sol-gel film for gate dielectric application was obtained by considering effects of surfactant, solvent, plasma treatment and curing process on the film characteristics. The reasons for leakage current variations of the sol-gel films prepared with different conditions were examined by a scanning electron microscope and Fourier-transform infrared analysis. The leakage current mechanism of the optimal sol-gel SiO 2 film was found to be dominated by Ohmic conduction. The characteristics of a-IGZO layers deposited with oxygen flow rates of 0-3 sccm were investigated. By integrating the optimal sol-gel SiO 2 dielectric and the sputtered a-IGZO layer, we successfully fabricated the TFT with a field effect mobility of 6.4 cm 2 /Vs. The interface trap density between the sol-gel SiO 2 and the a-IGZO layer was found to be 9.2 × 10 11 cm -2 eV -1 .

Transient photocurrent in hydrogenated amorphous silicon is studied in all relevant time regimes following the illumination of a pulse of light at one end of the sample. When both electron and hole transport are taken into consideration, we find that, at a low occupation level of trap states or at a low intensity of illumination, there are five well-defined current slopes. The first three are located at a short-time range, which has not been probed experimentally, and they are due to the electron transport. The last two slopes originate from the well-known phenomenon of hole transport. Each bend from a current slope change has a particular physical meaning and is interpreted. At a high illumination intensity, all five current slopes become less well-defined, and the two current slopes that are due to hole transport can change drastically because of significant space-charge effects. In particular, one of the hole slopes can even change from negative to positive, and the result is quite different from the well-known dispersive transport theory in disordered semiconductors.

The photoinduced transient current from an amorphous silicon thin-film transistor is computed and the mechanism described in terms of trap-state filling dynamics. The direction of the current flow and the location of the transient peak depends strongly on the distributions of donorlike and acceptorlike trap states in the neighborhood of the dark Fermi level. We show that the transient current can flow in the same direction as in the crystalline transistor, as well as in the opposite direction. There is also an interesting cross-over behavior in which the transient current flows out of the drain terminal as a pulse of positive charge, and then immediately reverses its direction. There is a broadening effect of the transient peak by a simultaneous switch on of the gate voltage. The transient peak typically occurs at 10−4 s and an example is provided. The transient current can be greatly diminished by switching the gate voltage long before illumination, or by doping the channel either partially or completely.