We have already reported on the pentacene photo FET having a photo-sensitive gate dielectric layer (poly(Nvinylcarbazole):
PVK). This photo FET showed excellent photo-switching properties upon illuminating the gate
dielectric layer, because the gate capacitor was rapidly charged up by providing a large amount of photo-generated
charges in the dielectric layer to the gate capacitor. When the gate bias and photo-illumination were turned off,
accumulated charges diffuse from the channel region to the source electrode and the channel immediately becomes OFF
state. Therefore, this photo FET can switch ON-OFF states rapidly, however, memory property is poor. In this study,
we have tried to give a memory function to the photo FET. For keeping the accumulated charges at the channel region
even after turning off the gate bias and photo-illumination, we intentionally formed Schottky barriers at the interface
between the semiconductor and the DS electrodes by using aluminum as a low work function metal instead of gold.
As a result, the photo FET did not show any gate voltage modulations of drain currents under dark condition. On the
other hand, the photo FET showed the drastic increase in drain current upon illuminating the gate dielectric layer.
Further, this high-drain current state was kept even after turning off the gate bias and photo-illumination (written state),
probably because the accumulated charges at the channel region could not escape from the source electrode owing to the
Schottky barrier at the semiconductor/DS electrodes interface. From these results, we have concluded that we could
develop the novel organic rewritable optical memory.