A true monolithic infrared photonics platform is within the reach if strain and bandgap energy can be independently engineered in SiGeSn semiconductors. However, this Si-compatible family of group-IV semiconductors is typically strained and inherently metastable, making the epitaxial growth fraught with extended defects and compositional gradients. Herein, we controlled the growth kinetics to achieve epitaxial Si0.06Ge0.90Sn0.04 layers lattice-matched to a Ge on Si substrate, with a uniform content and a thickness up to 1.5 {mu}m. Atomic-level studies demonstrated high crystalline quality and uniform composition and confirmed the absence of short-range ordering and clusters. Moreover, these layers exhibit n-type conductivity that is in striking difference to the commonly observed p-type behavior in GeSn and SiGeSn alloys. Room temperature spectroscopic ellipsometry and transmission measurements showed the enhanced direct bandgap absorption at 0.83 eV and a reduced indirect bandgap absorption at lower energies. Si0.06Ge0.90Sn0.04 photoconductive devices exhibit a dark current similar to that of Ge devices and a slightly higher room-temperature spectral responsivity reaching 1 A/W above 0.82 eV (i.e. below 1.5 {mu}m wavelengths). These results underline the enhanced performance in lattice-matched devices and pave the way to introduce SiGeSn semiconductors as building blocks to implement the long-sought-after silicon-integrated infrared optoelectronics.
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