Nonlinear photocurrent-intensity behavior of amorphous InZnO thin film transistors

摘要

The photocurrent (I_(PH)) of amorphous InZnO thin film transistors in the off-state is investigated as a function of incident optical power (P). The results show that I_(PH) exhibits a nonlinear dependence on P. Additionally, the dependence of I_(PH) on P exhibits a strong photon energy (hv)-dependent feature. When P is relatively low, I_(PH) is shown to be proportional to P~γ, where γ is greater than 1. The γ > 1 behavior may be ascribed to the source-barrier-lowering effect due to the accumulation of photo-induced positive charges at the source side. When P is relatively high, while I_(PH) remains proportional to P~γ under the incident light with hv larger than the optical bandgap (E_g) of a-IZO, it turns to increase at an exponential rate with P if hv of the incident light is smaller than the E_g. The exponential increase in I_(PH) is attributed to the source-barrier-thinning effect, which leads to a significantly enhanced tunneling current.