Radiation damage of Ge-on-Si devices

The radiation damage induced by 2-MeV electrons and 70-MeV protons in p+n diodes and p-channel MOS transistors, fabricated in epitaxial Ge-on-Si substrates is reported for the first time. For irradiation above 5×1015 e/cm2, it is noted that both the reverse and forward current increase, and that the forward current is lower after irradiation for a forward voltage larger than about 0.5 V. The reason for this might be an increased resistivity of the Ge-on-Si substrate. For p-MOSFETs, for a 1×1016 e/cm2 dose, a slight negative shift of the threshold voltage and a decrease of the drain current for input and output characteristics have been observed. In addition, gm decreases after irradiation. The degradation of the transistor performance is thought to be due to irradiation-induced positive charges in the high-κ gate dielectric. The induced lattice defects are also mainly responsible for the leakage current increase of the irradiated diodes.