Irradiation effects of 25 MeV silicon ions on SiGe heterojunction bipolar transistors

Abstract

Silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs) were exposed to 25MeV Si4+ ion with equivalent absorbed dose from 200krad(Si) to 10Mrad(Si). The transistor characteristics such as forward Gummel, reverse Gummel, leakage current of base–emitter (BE) junction and base–collector (BC) junction were studied before and after irradiation and were used to quantify the dose tolerance to the swift heavy ion irradiation. The base current was found more sensitive than collector current and current gain appeared to decline with the ion fluence increasing. On the reverse Gummel characteristics, besides the degradation in the base current, an unexpected increase in emitter current was observed with the ion fluence increasing. The output characteristics of the irradiated SiGe HBTs exhibited a decrease in the collector current with the increasing ion fluence. The reverse leakage current of BE and BC junctions increased with the increase in ion fluence. The self-annealing effect at room temperature was found less influence on the performance degradation. The displacement damages in the transistor were found to dominate the performance degradation of SiGe HBT after 25MeV Si4+ ion irradiation.