Current induced degradation in GaAs HBT's

A physical model for observed current gain degradation in GaAs heterojunction bipolar transistors (HBT's) is suggested in terms of a parameterized mathematical description of accumulating junction damage. The model and measurement suggest a positive correlation between high initial values of DC current gain and longer time to failure. Statistical analysis of accelerated stress failure data at 10 kA/cm/sup 2/ for InGaP-GaAs HBT's was conducted. The result shows projected median time to failure (MTTF) of more than 10/sup 8/ h at a junction temperature of 100/spl deg/C. The standard deviation is 0.6 and the activation energy is 1.5 eV.