EFFECT OF SURFACE-CHARGE AND COATING ON THE FIELD DISTRIBUTION OF SI HIGH-VOLTAGE THYRISTOR-LIKE STRUCTURES WITH BEVELED CONTOURS

Results of numerical calculations concerning the electric field distribution at the edge of bevelled p+np+-structures both in dependence on an assumed surface charge N(ss) and on the dielectric coating properties of the passivation substance are presented. It is shown that the amount of the peak electric surface field E(s)max at the edge of the structure is a sensitive function of the bevel angle theta as well as the polarity and concentration of the surface charge with the influence of the latter becoming rather weak in the case of small values of theta. However, a positive surface charge changes the breakdown characteristic of the structure mentioned for the worse in any case. In dependence on the bevel angle the value of E(s)max either passes through a maximum or decreases monotonously to zero in the whole range of surface charges investigated with the former (latter) case being valid for the negatively (positively) bevelled junction. Concerning the extension of the depletion layer width on the slanted edges of the device corresponding curves are obtained. The results presented can serve as a basis for the design of high-voltage thyristor structures.