An experimental study of reverse-bias second breakdown

Experimental results showing the influence of reverse-base current, case temperature, collector inductance, and peak collector current on the reverse-bias second breakdown (RBSB) behavior of high-voltage n+-p-n--n+power transistors are presented. The results are in qualitative agreement with the theory that avalanche injection initiates RBSB. The inductance and peak collector current results are in conflict with the theory that RBSB is initiated at a critical temperature. It is concluded that for these devices for the condition studied, RBSB is not initiated at a critical temperature. It is shown that the theory of current focusing, in conjunction with the theory of avalanche injection, does not accurately predict the RBSB conditions during device sustaining. It is proposed that other mechanisms in addition to current focusing contribute to the nonuniformity of current during transistor turnoff.