Direct-gap photoluminescence with tunable emission wavelength in $Ge1−ySny$ alloys on silicon

Direct-gap photoluminescence has been observed at room temperature in $Ge1−ySny$ alloys grown on (001) Si substrates. The emission wavelength is tunable over a 90 meV (200 nm) range by increasing the Sn concentration from $y=0$ to $y=0.03$⁠. A weaker feature at lower energy is assigned to the indirect gap transitions, and the separation between the direct and indirect emission peaks is found to decrease as a function of $y$⁠, as expected for these alloys. These results suggest that $Ge1−ySny$ alloys represent an attractive alternative to Ge for the fabrication of laser devices on Si.