MODELING THE POST-BURN-IN ABNORMAL BASE CURRENT IN ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS/

The base current of AlGaAs/GaAs heterojunction bipolar transistor subj ected to a long burn-in test often exhibits an abnormal characteristic with an ideality factor of about 3, rather than a normal ideality fac tor between 1 and 2, in the midvoltage range, We develope an analytica l model to investigate the physical mechanisms underlying such a chara cteristic. Consistent with the finding of an experimental work reporte d recently, our model calculations show that the recombination current in the base has an ideality factor of about 3 in the midvoltage range and that such a current is responsible for the observed abnormal base current in heterojunction bipolar transistor after a long bum-in test . Post-burn-in data measured from two different heterojunction bipolar transistors are also included in support of the model. (C) 1996 Ameri can Institute of Physics.