Influence of bevel angle and surface charge on the breakdown voltage of negatively beveled diffused p- n junctions

Abstract

An analytical study has been made of the breakdown voltage of negatively beveled ∗ ∗ A negatively beveled p- n junction is defined as having an increasing area going from the heavily doped side of the junction to the lightly doped side. Positively beveled means the opposite. high-voltage diffused p- n junctions with substrate doping concentration. N S , in the range of 10 13 cm 3-2 × 10 14 cm 3 . uniform surface charge concentration in the range from N SC = 5 × 10 11 cm 2 (negative) to N SC = 10 12 cm 2 (positive), diffusion depth x j = 90 μm and negative bevel angle between 0·5 and 6 degrees. A comparison with experimental breakdown data and with i.r.-thermometer measurements support the model for the breakdown process. According to the model avalanche breakdown occurs along a current path passing through a point of maximum electric field which develops below the semiconductor surface on the highly doped side of the junction. The location of the point of maximum field and the value of the field are influenced by the bevel angle and the polarity and concentration of surface charge. The surface charge is shown to have a decisive influence on the breakdown voltage of negatively beveled p- n junctions.