Lower limit of method for the extraction of ionization coefficients from the electrical characteristics of heterojunction bipolar transistors

The error contributed by the Early effect to the ionization coefficient obtained from the characteristics of heterojunction bipolar transistors (HBTs) is calculated. For the case of InP-GaInAs HBTs, the Early effect does not introduce a significant error at low electric fields. For the case of HBTs with Ga/sub 0.28/In/sub 0.72/As/sub 0.61/P/sub 0.39/ (/spl lambda/=1.3 /spl mu/m) base and collector, the Early effect introduces a relatively large error at low electric fields, A procedure for correcting this error is outlined. It is found that the low field ionization coefficient in Ga/sub 0.28/In/sub 0.72/As/sub 0.61/P/sub 0.39/ exhibits an anomalous low field behavior, similar to that of Ga/sub 0.47/In/sub 0.53/As.