Uniform turn-on in four-layer diodes

The turn-on characteristics of 200-volt four-layer diodes have been investigated as a function of the rate of rise of the applied voltage close to the breakover point. A fast rate of rise of the order of kv/µsec allows bringing the voltage up to, or higher than, the designed avalanche voltage of the center junction, even if localized spots having a lower breakdown voltage are present. Such spots, possibly due to crystalline defects, surface conditions and statistical or accidental variations of impurity concentration, may lead to localized turn-on and possible burn out. There is experimental evidence that a fast rate of rise results in uniform turn-on and allows current densities up to 55,000 a/cm²without damaging the device.