Nonlinear photocurrent-intensity behavior of amorphous InZnO thin film transistors

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 (h nu)-dependent feature. When P is relatively low, I-PH is shown to be proportional to P-gamma, where gamma is greater than 1. The gamma > 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-gamma under the incident light with h nu larger than the optical bandgap (E-g) of a-IZO, it turns to increase at an exponential rate with P if h nu 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. Published by AIP Publishing.