Effects of electron irradiation on SiGe devices

The degradation and the recovery behavior of the device performance for SiGe diodes and p-MOSFETs irradiated by 2-MeV electrons are reported. For diodes, it is noted that both the reverse and forward current increase by irradiation. An interesting observation is that the forward current decreases after irradiation for a forward voltage larger than ∼ 0.7 V. This reduction can be explained by an increased resistivity of the Si substrate. The degradation recovers by thermal annealing after irradiation. For a fluence of 1 x 1015 e/cm2, the diode performance almost recovers to the initial condition after 250 oC annealing. For the transistors, after irradiation, a slight negative shift of the threshold voltage and a decrease of the drain current for input and output characteristics have been observed together with a decrease of hole mobility. This is mainly due to the increase of the threshold voltage induced by positive charge trapping in the gate oxide.