Degradation differences in the forward and reverse current gain of 25 MeV Si ion irradiated SiGe HBT

The silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs) were exposed to 25 MeV Si ions with ion fluence from 9.1×108 to 4.46×1010 ions/cm2 at room temperature. The forward current gain (βF) and reverse current gain (βR) were studied before and after irradiation and the bias dependences of the displacement damage factor for βF and βR were also presented. Measurement results indicated that βF and βR all decline with the ion fluence increasing. The reciprocal of βR was found to vary linearly throughout all ion fluence for arbitrary base-collector voltage. However, a non-linear behavior for the reciprocal of βF appeared at low fluence for the low and medium base-emitter voltage. Besides, it was found that the bias dependence of displacement damage factor for βF was significantly different from that for βR. The underlying physical mechanisms were analyzed and investigated in detail.