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

The hole-initiated impact ionization multiplication factor M-p-1 and the io nization coefficient alpha (p) in AlGaAs/InGaAs p-n-p heterojunction bipola r transistors (HBTs) are presented. A large discrepancy is observed at low electric field when the measured data from the p-n-p HBTs are compared with those given from avalanche photodiode. The results show that the conventio nal impact ionization models, based on local electric field, substantially overestimate the hole impact ionization multiplication factor M-p-1. We bel ieve that the hole ionization coefficient in p-n-p HBTs where significant d ead space effects occur in the collector space charge region. (C) 2000 Amer ican Institute of Physics. [S0003- 6951(01)04001-3].