Degradation and recovery of proton irradiated Si1-xGe x epitaxial devices

Irradiation damage in n⁺-Si/p⁺-Si_1-x Ge_x/n-Si epitaxial diodes and heterojunction bipolar transistors (HBTs) by protons is studied as a function of germanium content, proton fluence and energy for the first time. The degradation of the electrical performance of devices increases with increasing fluence, while it decreases with increasing germanium content and energy. The induced lattice defects in the Si_1-xGe_x epitaxial layers and the Si substrate are studied by DLTS methods. In the Si_1-xGe_x epitaxial layers for diodes, electron capture levels associated with interstitial boron complex are induced by irradiation, while two electron capture levels corresponding to the E center and the divacancy are observed in the collector region of the HBTs. The influence of the radiation source on device degradation is then discussed taking into account the number of knock-on atoms and the nonionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects. In order to examine the recovery behavior, isochronal thermal annealing is carried out for temperatures ranging from 75 to 300°C. Based on the recovery of electrical performance, it is pointed out that the electron capture levels induced in the Si_1-xGe_x epitaxial layers are mainly responsible for the increase of reverse diode current