Sharp MIR plasmonic modes in gratings made of heavily doped pulsed laser-melted Ge1-xSnx

Plasmonic structures made out of highly doped group-IV semiconductor materials are of large interest for the realization of fully integrated mid-infrared (MIR) devices. Utilizing highly doped Ge1-xSnx alloys grown on Si substrates is one promising route to enable device operation at near-infrared (NIR) wavelengths. Due to the lower effective mass of electrons in Sn compared to Ge, the incorporation of Sn can potentially lower the plasma wavelength of Ge1-xSnx alloys compared to that of pure Ge. However, defects introduced by the large lattice mismatch to Si substrates as well as the introduction of alloy scattering limit device applications in practice. Here, we investigate pulsed laser melting as one strategy to increase material quality in highly doped Ge1-xSnx alloys. We show that a pulsed laser melting treatment of our Ge1-xSnx films not only serves to lower the material's plasma frequency but also leads to an increase in active dopant concentration. We demonstrate the application of this material in plasmonic gratings with sharp optical extinction peaks at MIR wavelengths.