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The electrical characteristics of wafer-bonded non-doped germanium-on-insulator (GOI) substrates were investigated using a four-point-probe pseudo-metal–oxide–semiconductor field-effect transistor. Annealing the wafer-bonded GOI substrates in vacuum strongly influenced their electrical characteristics. GOI samples annealed at temperatures below 500 °C exhibited n-channel depletion transistor operation, whereas GOI samples annealed at temperatures between 550 and 600 °C exhibited p-channel depletion transistor operation. The carrier mobility strongly depended on the sweep direction of the gate voltage; this characteristic disappeared after annealing at temperatures above 550 °C. The dependence of the electrical characteristics on the annealing temperature is explained in terms of the influence of the defect states on energy band bending near the interface.

The sulfide morphology in SUS303 was investigated and the mechanism of monotectic sulfide formation was evaluated. The sulfide of metastable monotectic type was observed at the surface region of ingot with the higher solidification cooling rate and stable eutectic type was observed at the inner region. The formation of monotectic sulfide was promoted by Ca addition and the formation of eutectic type sulfide was promoted by Al addition with the lower oxgen content. It is thought that the nucleation behavior greatly affect the monotectic sulfide formation because of the lower interfacial energy with liquid oxide inclusion. However, solute distribution, undercooling and the decrease of S activity by adding Ca or increasing O content may also influence on the eutectic/monotectic morphology selection.