Sulfur passivation of Ge(100) is achieved using aqueous ammonium sulfide (NH4)2S(aq). The passivation layer is largely preserved after atomic layer deposition of the high-κ dielectric material HfO2 when sufficiently low growth temperatures (e.g., 220°C) are employed. Oxygen incorporation is moderate and results in an electrically passivating GeOS interface layer. The HfO2∕GeOS∕Ge gate stack exhibits lower fixed charge and interface state density than a more conventional HfO2∕GeON∕Ge gate stack fabricated via an ammonia gas treatment.

This paper reviews progress and current critical issues with respect to the integration of germanium (Ge) surface-channel MOSFET devices as well as strained-Ge buried-channel MOSFET structures. The device design and scalability of strained-Ge buried-channel MOSFETs are discussed on the basis of our recent results. CMOScompatible integration approaches of Ge channel devices are presented.

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We report on physical and electrical characterization of ultrathin (3–10nm) high-κHfO2 gate stacks deposited on Ge(100) by atomic-layer deposition. It is observed that uniform films of HfO2 can be deposited on Ge without significant interfacial growth. The lack of an interlayer enables quasiepitaxial growth of HfO2 on the Ge surface after wet chemical treatment whereas a nitrided interface (grown by thermal oxynitridation in ammonia) results in an amorphous HfO2. The stacks exhibit surprisingly good thermal stability, up to temperatures only 150°C below the melting point of Ge. In terms of electrical properties, HfO2 on Ge shows significantly reduced (up to 4 decades) gate leakage currents in the ultrathin regime of equivalent electrical thickness down to ∼1.4nm due to the high-dielectric constant of ∼23. Nitrided interface is observed to be important for good insulating properties of the stack.