Characterizing and modeling current gain degradation in bipolar transistor exposed to heavy ion radiation

Radiation effects of 20 MeV Br on bipolar transistors are investigated in this work. A distinct different bias dependences are found for damage factors (DF) of forward and reverse current gain. For reverse current gain, DF gradually decreases with the voltage across base-collector junction (V_BC) increasing, until a saturated value is reached. While an unexpected increase exists in DF of forward current gain over the high voltage across base-collector junction (V_BE) region. The high injection effect is found to contribute to the observed rebound for forward current gain over high V_BE region. From the device physical perspective, a physics-based analytical closed DF model for forward and reverse current gain is proposed, including the contribution of high injection effect and recombination current in junction space charge region. A good agreement is obtained between the measured and modeled data over the whole bias region.