  The development of Si-compatible active photonic devices is a high priority
in computer and modern electronics industry. Ge is compatible with Si and is a
promising light emission material. Nearly all Ge-on-Si materials reported so
far were grown using toxic precursor gases. Here we demonstrate the creation of
Ge films on Si substrates through physical vapor deposition of toxin-free solid
Ge sources. Structural characterization indicates that a high tensile strain is
introduced in the Ge film during the deposition process. We attribute the
presence of such a tensile strain to the difference in thermal expansion
coefficient between Si and Ge. A Ge peak, centered at ~2100 nm, is evident in
the photoluminescence spectra of these materials, which might result from
direct band gap photoluminescence alone, or from superposition of direct band
gap and indirect band gap photoluminescence. These Ge-on-Si materials are
therefore promising in light emission applications.
