  Excitons are promising candidates for generating superfluidity and
Bose-Einstein Condensation (BEC) in solid state devices, but an enabling
material platform with in-built bandstructure advantages and scaling
compatibility with industrial semiconductor technology is lacking. Here we
predict that spatially indirect excitons in a lattice-matched strained Si/Ge
bilayer embedded into a germanium-rich SiGe crystal, would lead to observable
mass-imbalanced electron-hole superfluidity and BEC. Holes would be confined in
a compressively strained Ge quantum well and electrons in a lattice-matched
tensile strained Si quantum well. We envision a device architecture that does
not require an insulating barrier at the Si/Ge interface, since this interface
offers a type II band alignment. Thus the electrons and holes can be kept very
close but strictly separate, strengthening the electron-hole pairing attraction
while preventing fast electron-hole recombination. The band alignment also
allows a one-step procedure for making independent contacts to the electron and
hole layers, overcoming a significant obstacle to device fabrication. We
predict superfluidity at experimentally accessible temperatures of a few Kelvin
and carrier densities up to $\sim 6\times 10^{10}$ cm$^{-2}$, while the large
imbalance of the electron and hole effective masses can lead to exotic
superfluid phases.
