Modeling the abnormal base current in post-burn-in AlGaAs/GaAs heterojunction bipolar transistors

The base current of AlGaAs/GaAs heterojunction bipolar transistor subjected to a long burn-in test often exhibits an abnormal characteristic with an ideality factor of about 3, rather than a normal ideality factor between 1 to 2, in the mid-voltage range. This paper develops an analytical model to investigate the physical mechanisms underlying such a characteristic. Our model calculations show that the recombination current in the base has an ideality factor of about 3 in the mid-voltage range and that such a current is responsible for the observed abnormal base current in heterojunction bipolar transistor after a long burn-in test. Post-burn-in data measured from two different heterojunction bipolar transistors are also included in support of the model.