Theory of switching phenomena in metal/semi-insulator/ n- p+ silicon devices

Abstract

The theory of switching is presented for a structure consisting of a p +- n junction and a metal electrode separated from the N-section of the p +- n junction by a semi-insulating (leaky) layer. When a negative bias is applied to the electrode, the section of the n-layer under the electrode goes into deep depletion. In this mode, the current through the device is limited by generation in the deeply depleted region. This is the high-impedance or OFF state of the device. At a sufficiently high voltage, the switching voltage, V s , the p +- n junction is turned on by either avalanching in the n-layer or by the deep-depletion region extending through to the p +- n region (punch-through). When the junction turns on, the n-section goes from deep-depletion towards inversion. Thus, the voltage across the device decreases with a concomitant increase in the current through the device. This is the switching mode. The switching voltage may be tailored by varying the doping and/or width of the n-section. Following switching, the device comes into the steady-state when the current through the insulating layer is equal to the current flowing across the p +- n junction. The I-V characteristic of this highly conducting (ON state) mode is determined principally by the I-V characteristic of the semi-insulating film. By suitable choice of material this portion of the characteristic can approach zero dynamic impedance, i.e. a near-vertical characteristic, characterized by a low holding voltage. Capacitance and switching characteristics of the device are also discussed.