Germanium-rich silicon-germanium films epitaxially grown by ultrahigh vacuum chemical-vapor deposition directly on silicon substrates

We have grown device quality germanium-rich silicon-germanium films on silicon substrates using a two-step ultrahigh vacuum chemical-vapor deposition growth process. The films have thermally induced tensile strain, resulting in a direct band gap reduction of similar to 30 meV, in agreement with what we observe for similarly grown pure germanium films. Our data suggest that alloying of silicon increases the band gap reduction with strain at the high germanium end of the composition range. Annealing of the films allows for reduction in the dislocation density to 2x10(7)/cm(2), comparable to what we achieve in pure germanium films and showing that alloying small amounts of silicon does not inhibit dislocation motion. p-i-n diodes fabricated from these films using a silicon compatible process exhibit reverse leakage currents of similar to 10 mA/cm(2) at 0.5 V reverse bias. The responsivity of a Si0.04.8Ge0.952 diode was measured at 0.23 A/W at 1280 nm, demonstrating the high quality of these epitaxial films. (c) 2007 American Institute of Physics.