High-Mobility MOSFETs Fabricated on Continuous, Wafer-Scale Ge Films Epitaxially Grown on Si

We report the material characterization of continuous, wafer-scale Ge films epitaxially grown on Si by molecular beam epitaxy. The material quality of Ge is further tested by fabricating high-mobility, long-channel MOSFETs. Our growth technique makes use of a thin chemical SiO₂ template with nanoscale windows and carefully timed thermal annealing during the initial stage of island coalescence. The resulting defect density in n- and p-type Ge is ~2 × 10⁵ and 5 × 10⁷ cm^-2. The MOSFETs are then fabricated on these substrates, where the gate-stack consists of Ti/HfO₂/GeO_xN_y/Ge-on-Si. The GeO_xN_y interlayer is used to effectively passivate the Ge surface. The subthreshold slope is ~100 and ~200 mV/decade for p- and n-MOSFETs, compared with ~80 mV/decade for p-MOSFETs built on bulk-Ge substrates. The p- and n-MOSFETs also show enhanced peak effective hole and electron mobilities of 400 and 950 cm²/V-s that are 82% and 30% increase over the universal mobilities in Si.