DEGRADATION OF SI1-XGEX EPITAXIAL HETEROJUNCTION BIPOLAR-TRANSISTORS BY 1-MEV FAST-NEUTRONS

Irradiation damage in n(+)-Si/p(+)-Si1-xGex/n-Si epitaxial heterojunct ion bipolar transistors (HBTs) by 1-MeV fast neutrons is studied as a function of fluence and germanium content for the first time. The degr adation of the electrical performance of HBTs by irradiation increases with increasing fluence, while it decreases with increasing germanium content. The induced lattice defects in the base and the collector re gions are studied by DLTS methods. In the base region, electron captur e levels associated with interstitial boron are induced by irradiation , while two electron capture levels corresponding to the E centers and the divacancy are formed in the collector region. The device degradat ion of performance is then correlated with simulations of numbers of k nock-on atoms. In order to examine the recovery behavior, isochronal t hermal annealing is carried out for temperatures ranging from 75 to 30 0 degrees C. Based on the recovery of electrical performance, it is po inted out that the electron capture levels induced in the base and col lector regions are mainly responsible for the increase of base current and the decrease of collector current.