PURPOSE: To make an integrated dynamic optical neuro-chip by providing a photo detector with a variable sensitivity function and a memory function.
CONSTITUTION: When emitted light reaches a depletion layer 10 via an insulating film 5, a control gate 3, and a floating gate 4, a photo electric current is generated. The rate of generation of the photo electric current, or sensitivity, is determined by bias voltage Vb applied to one Schottky electrode 7. The sensitivity is approximately proportional to the bias voltage Vb and the polarity of the photo electric current changes depending on the polarity of the voltage Vb. The sensitivity is also proportional to the thickness of the depletion layer 10 and the thickness of the depletion layer 10 is proportional to the potential Vfg of the floating gate 4. That is, when the voltage Vb is changed the potential Vfg changes. Hence the sensitivity can be changed, the polarity of the photo electric current generated in the layer 10 is changed, and an optical integrated circuit suitable for an optical neuro-network is made.