Ge films were epitaxially grown on GaAs͑100͒ substrates and Ga 0.88 In 0.12 As͑100͒ virtual substrates using an ultrahigh vacuum/ chemical vapor deposition system. The incubation time of Ge growth depends on Ga͑In͒As surfaces that were processed by different wet chemical solutions. Growth behaviors, such as island growth at the initial stages and selective growth into recessed regions of GaAs, were studied by transmission electron microscopy. To test the quality of Ge grown on GaAs, an n + -Ge/p-GaAs diode was fabricated. We propose that through Ge selective epitaxial growth, Ge can be used as the source-drain of a GaAs metal-oxide-semiconductor field-effect transistor ͑MOSFET͒ to overcome some intrinsic limitations of this device.

We investigated the selective growth of germanium into nanoscale trenches on silicon substrates. These nanoscale trenches, the smallest size of which was 50 nm, were fabricated using the state-of-the-art shallow trench isolation technique. The quality of the Ge films was evaluated using transmission electron microscopy. The formation of threading dislocations ͑TDs͒ was effectively suppressed when using this deposition technique. For the Ge grown in nanoscale Si areas ͑e.g., several tens of nanometers͒, the TDs were probably readily removed during cyclic thermal annealing predominantly because their gliding distance to the SiO 2 sidewalls was very short. Therefore, nanoscale epitaxial growth technology can be used to deposit Ge films on lattice-mismatched Si substrates with a reduced defect density.

The demonstration of a salicidelike self-aligned contact technology for III-V metaloxide-semiconductor field-effect transistors ͑MOSFETs͒ is reported. A thin and continuous crystalline germanium-silicon ͑GeSi͒ layer was selectively formed on n + doped gallium arsenide ͑GaAs͒ regions by epitaxy. A new self-aligned nickel germanosilicide ͑NiGeSi͒ Ohmic contact with good morphology was achieved using a two-step annealing process with precise conversion of the GeSi layer into NiGeSi. NiGeSi contact with the contact resistivity ͑ c ͒ of 1.57 ⍀ mm and sheet resistance ͑R sh ͒ of 2.8 ⍀ / ᮀ was achieved. The NiGeSi-based self-aligned contact technology is promising for future integration in high performance III-V MOSFETs.

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