In/MgSe Terahertz Filters with Enhanced Optical Conduction and Light Absorption

In this work, semitransparent indium thin films with thickness of 200 nm were used as substrates for depositing magnesium selenide thin films (200 nm). Both indium and MgSe films were coated onto ultrasonically cleaned glass substrates under vacuum pressure of 10^–5 mbar. The structural and morphological studies on these thin films showed that indium conducting layers suppressed the formation of cubic MgSe₂ phase in the films. Optically, it was observed that semitransparent indium substrates improved the light absorption in the visible and infrared ranges of light. The light absorption increased by more than 14 times at 1.20 eV. In addition, coating MgSe onto In substrates resulted in a shift in the direct allowed transitions band gap from 2.54 eV to 1.92 eV. It also decreased the dielectric constant values. The optical conductivity and terahertz cutoff frequency values increased at the In/MgSe interfaces. Fitting of the optical conductivity spectra of In/MgSe interfaces by Drude–Lorentz approaches showed that indium substrates increased the drift mobility by two times and increased the plasmon frequency of MgSe. The enhanced optical conductivity and increased terahertz cutoff frequency values which are achieved via coating MgSe onto semitransparent indium substrates make MgSe films applicable in terahertz technology as band filters.