Copper doping effects on the optical and dielectric properties of amorphous indium selenide thin films

In this study, to enhance their optoelectronic performances, amorphous indium selenide (a-InSe) thin films were doped with copper using the thermal evaporation technique under a vacuum pressure of 10–5 mbar. The aim was to investigate the impact of Cu doping on the optical absorption, energy band gap, dielectric dispersion, optical conduction, and terahertz cutoff frequency. Notably, Cu doping levels of 1.41 at.% and 2.97 at.% in a-InSe resulted in a significant enhancement in light absorption by more than three and four times, respectively, without significantly altering the energy band gap. Furthermore, Cu doping led to a remarkable increase in the dielectric constant value and caused a redshift in the position of the dielectric resonance peak. Moreover, a noticeable enhancement in the optical conductivity and terahertz cutoff frequency values was observed in a-InSe films doped with 2.97 at.% of Cu. The Drude-Lorentz fittings of the optical conductivity data demonstrated that the presence of Cu atoms increased the scattering time at the femtosecond level and enhanced the drift mobility from ~ 5.0 cm2/Vs for undoped films to ~ 113 cm2/Vs for 2.97 at.% Cu-doped films. Additionally, the range of the terahertz cutoff limit expanded, covering a range of 0.1–16 THz. The study indicate that the features exhibited by Cu-doped InSe hold promise for various optoelectronic applications including terahertz technology.