Optical characterization of the MgO/InSe interface

In this work, a 500 nm thick MgO layer deposited on the physically evaporated amorphous InSe thin film substrate is designed as a window for the MgO/InSe terahertz resonators. The optical properties including the reflectance and the dielectric constant dependence on the angle of incidence (θi), the normal transmittance, and the absorption coefficient of the interface were investigated in the range of ∼270–1000 THz. It was observed that the total reflectivity of the substrate continuously decreases with increasing θi in the range of 33–80°. The spectra of InSe and MgO/InSe revealed strong dielectric resonance patterns below 450 THz. The energy bands of the direct allowed transitions in InSe film shrunk from 3.90, 2.75, and 1.49 eV to 3.71, 2.10, and 0.96 eV when MgO was deposited onto the InSe film. By analyzing the dielectric spectra, we were able to determine the static and lattice dielectric constants in addition to the oscillator and dispersion energies. The latter energy increased from 27.43 to 35.84 via interface construction.