Analysis and modelling of the bistable behavior of an optically switching tunnel MOS diode

Metal Oxide Semiconductor (MOS) devices with two stable states observed through their electrical characteristics have been previously reported by several authors. Structures like MISS (metal - insulator - semiconductor switches), MIST (metal - insulator - semiconductor - thyristor), MIS-SIM (metal - thin insulator - crystalline silicon (n-p) - thin insulator - metal), and modifications of those are known. We present in this work an analysis of the biestable behavior observed in simple MOS capacitors, produced by the semiconductor departure from thermal equilibrium due to two mechanisms: i) extraction by tunnel of minority carriers from the inversion layer responsible of the stabilization of the device in a stable state of low capacitance (high impedance) and ii) impact ionization which sustain the device in a different state of high capacitance now impedance). We also present a model describing the relaxation to the first state of high impedance immediately after the device is pulsed into deep depletion and the return to the low impedance state after a light pulse. The proposed device can be used as a photoswitch, radiation detector, or it can be the elementary cell for an optically written memory; and it has a simpler structure than the above mentioned devices having similar behavior.