Improvement effect of electrical properties in post-annealed wafer-bonded Ge(001)-OI substrate

We investigated the electrical properties of non-doped wafer-bonded germanium-on-insulator substrates (Ge(001)-OI) post-annealed in various ambiences using a pseudo-metal-oxide-semiconductor field effect transistor. The transistor operation in the Ge(001)-OI without post-annealing was observed in the n-channel mode with hysteresis in the channel conductance versus gate voltage curves. The n-channel transistor operation was depletion type, with a large threshold voltage shift from the ideal threshold voltage (∼0 eV). Upon post-annealing the Ge(001)-OI, the behavior of the hysteresis and threshold voltage shift caused by interface defects was improved, which strongly depended on the post-annealing condition. Post-annealing in a N₂ ambience yielded the most effective improvement, which included some O₂ gas. This improvement is presumably because oxygen vacancies near the Ge/SiO₂ interfaces are reduced by the oxygen supply during the post-annealing treatment.