Enhanced crystallinity, optical conductivity and terahertz cutoff frequency of stacked layers of FeSe2 by Al nanosheets

Abstract

Herein a 250 nm thick two stacked layers of FeSe2 (abbreviated as FF) thin films and FF stacks comprising aluminum nanosheets of thicknesses of 50 nm (FAF) are studied. Amorphous FeSe2 thin films are deposited using thermal evaporation technique under a vacuum pressure of 10−5 mbar. It is observed that insertion of Al nanosheets induced the evolution of orthorhombic phase of FeSe2. nanowire and elongated rectangular grains are also formed. Optically Al nanosheets enhanced the light absorption by 4.1 times and redshifted the indirect/direct energy band gaps from 2.80/2.49 eV to 2.42/1.85 eV, respectively. It also improved the optical conductivity and terahertz cutoff frequency as well. In addition the optical conductivity parameters of FF and FAF terahertz resonators are determined by the Drude-Lorentz approach. It is observed that in the infrared range of light Al nanosheets improved the drift mobility of FF from 2.06 cm2/Vs to 12.55 cm2/Vs. The hole density is reduced and the scattering time constant at femtosecond level is increased. FF and FAF terahertz resonators performed as optical filters suitable for terahertz technology applications with terahertz cutoff frequency varying in the range of 17.2–300 THz.