A Transient Component in the Breakdown Voltage of Silicon P-N Junction Rectifiers

The Electronic Component Reliabilty Center at Battelle Memorial Instiute is involved in a continuing study of physical mechanisms and processes in electronic arts pertinent to device reliability. In a study of avalanche breakdown in diffused silicon p-n junctions, an exponential decrease with time ahas been observed in the onset voltage for microplasma conduction. The time constant of this decrease is inversely proportional to the ratio of average on- to off-time of the microplasma pulses, and the magnitude is temperature dependent, peaking at approximately 60° K. The theory is advanced that, during the avalanche pulse, the acquisition rate of electrons by ionized donor impurities is increased, decreasing the ionized donor concentration, thus changing the field intensity and hence the breakdown voltage. In effect, compensating donor sites tend to fill during the microplasma pulses and empty in the internals between pulses. Thus, ΔND (t) = rfTon - re Toff, where rf and re are the filling and emptying rates, respectively, and Ton and Toff are the relative average on- and off-times of the microplasma pulses. At temperatures where the Fermi level is several kT from the energy level of the trapping sites, the occupation index of the traps is relatively unaffected by injected carrier density. However, where EF is within a few kT of ET, the occupation density of the traps is a strong function of the injected carrier density.