SURFACE BREAKDOWN OF SILICON

The surface electrical breakdown of n+ nn+ rectangular solid blocks of silicon have been investigated. These studies were conducted in air at pressures of 10(-6) Torr and 1 atm, and in transformer oil, ethylene glycol, and de-ionized water, with pulsed electrical excitation. In addition, one sample had one contact end coated with a material having a large dielectric constant. It was found that the breakdown voltage of these devices increased as the dielectric constant of the ambient increased. Glow discharge cleaning of the surface in vacuum had no effect on the breakdown voltage. Based on these results a theory of surface charging leading to field enhancement along the surface is presented. Furthermore, the surface charge perturbs the space-charge region at the n + n anode junction such that the field at the junction increases more along the surface than in bulk. As the field increases, it is hypothesized that collision ionization occurs, leading to avalanche breakdown. It is shown that a large dielectric constant material in contact with the surface near the junction can lead to significant improvement in the voltage holdoff capability of the silicon blocks.