Edge inversion channels and surface leakage currents in high-voltage semiconductor devices

Abstract

It is shown that the electric field over the surface of semiconductor devices can be sufficient to induce edge inversion channels if the bias voltage is high and the surface charge density Qs is low. In this case, the edge region of the devices containing the p-n-p structure (e.g., that of thyristors) functions as a planar pchannel MIS transistor with a combined gate and drai n and the entire medium over the surface functions as the gate insulator. The current between the source and drain of this "edge MIS transistor" is the surface leakage current of the entire device. An analytical theory describing the current-voltage characteristic in the subthreshold mode is developed. It is shown that this new mechanism controls the total leakage current of highvoltage devices if | Q s | and temperature T are small enough (|Q s | < 4 nC/cm 2 , T < 270 K and |Q s | < 58 nC/cm 2 , T < 600 K for silicon and silicon carbide devices, respectively).