  A true monolithic infrared photonics platform is within reach if strain and
bandgap energy can be independently engineered in SiGeSn semiconductors.
Herein, we investigate the structural and optoelectronic properties of a 1.5
{\mu}m-thick Si0.06Ge0.90Sn0.04 layer that is nearly lattice-matched to a Ge on
Si substrate. Atomic-level studies demonstrate high crystalline quality and
uniform composition and show no sign of short-range ordering and clusters. Room
temperature spectroscopic ellipsometry and transmission measurements show
direct bandgap absorption at 0.83 eV and a reduced indirect bandgap absorption
at lower energies. Si0.06Ge0.90Sn0.04 photoconductive devices operating at room
temperature exhibit dark current and spectral responsivity (1 A/W below 1.5
{\mu}m wavelengths) similar to Ge on Si devices, with the advantage of a
near-infrared band gap tunable by alloy composition. These results underline
the relevance of SiGeSn semiconductors in implementing a group IV material
platform for silicon-integrated infrared optoelectronics.
