Damages of Ge devices by 2-MeV electrons and their recovery

The degradation and recovery behavior of the device performance of Ge diodes and p-Ge MOSFETs irradiated by 2-MeV electrons are studied. For diodes, it is noted that both the reverse and forward current increase after irradiation. However, 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 n-well in the germanium substrate. For the transistors, after irradiation, a slight negative shift of the threshold voltage and a decrease of the drain current input and output characteristics have been observed together with a decrease of the hole mobility. This is mainly due to the increase of the absolute value of the threshold voltage induced by positive charges in the gate oxide. The degradation recovers by thermal annealing after irradiation. For 1 × 1017 e/cm2, the diode performance almost completely recovers to the initial condition after a 250 °C annealing and the anneal process is characterized by an activation energy of 0.59 eV. For transistor irradiated to 5 × 1017 e/cm2, the device performance also recovers but with an activation energy of 0.33 eV.