Two Dimensional Transient Simulations of Hydrogenated Amorphous Silicon Thin Film Transistors.

In this dissertation, the first accurate two-dimensional simulations of transient behaviors in hydrogenated amorphous silicon thin-film transistors are studied. The trap charge density along, or transverse to, the direction of the semiconductor channel is highly nonuniform and the trap filling time dominates the switching time as compared to the transit time, which is about four orders of magnitude smaller. Near both contacts, direction of the transverse current is always upwards toward the insulator-semiconductor interface due to the strong electric fields. However, at the central region of the channel, the transient current is quite complex and is discussed. When the channel length varies from 2 to 10 mum, the switching-on time is of the order of 10^{-3} s. The occupation function everywhere displays a partial filling of higher energy trap states during the switch -on. This is in contrast to results presented by other investigators. The relation between the transit time and the switch-on time with respect to the amount of trap states is presented. The absence of the drain current peak, which is contrary to the results reported by other investigators, is discussed. Finally, trap filling levels during the switch-on are studied.