Avalanche multiplication and ionization coefficient in AlGaAs/InGaAs p-n-p heterojunction bipolar transistors

The hole-initiated impact ionization multiplication factor M/sub p/-1 and the ionization coefficient /spl alpha//sub p/ in AlGaAs/InGaAs p-n-p heterojunction bipolar transistors are presented. A large departure is observed at low electric field when comparison is made between the measured data and those obtained from avalanche photodiode measurements. The results show that the conventional impact ionization models, based on local electric field, substantially overestimate the hole impact ionization multiplication factor M/sub p/-1 and the hole ionization coefficient in p-n-p heterojunction bipolar transistors where significant dead space effects occur in the collector space charge region.