Comparative investigation of linear and nonlinear optical properties of As–70 at% Te thin films: influence of Ga content

Abstract

Thin films (~ 150 nm) of amorphous As30Te70−xGax (where x = 0, 1, 3, 6, and 10 at%) are prepared through thermal evaporation of As30Te70−xGax bulk samples on glass substrates. X-ray powder diffraction (XRD) analysis reveals the amorphous nature of the as-prepared As30Te70−xGax thin films. The influence of Ga content on the As30Te70−xGax thin films’ linear and nonlinear optical properties is determined based on the optical reflectance and transmittance spectra. The estimated (direct or indirect) optical bandgap decreases with an increase in Ga content up to 3 at% and then increases, whereas the Urbach energy exhibits an opposite trend. The linear and nonlinear refractive indices, extension coefficient, optical conductivity, electrical conductivity and nonlinear susceptibility, optical density, inter-band transition strength, etc., are found to be significantly influenced by Ga content and the energy of incident waves. The As30Te67Ga3 composition can be considered as a puzzling compound as most of the investigated parameters in As30Te70−xGax alloys demonstrate opposite behaviors around that composition. Moreover, the optical surface resistance and thermal emission of As30Te70−xGax thin films are estimated from the investigated optical parameters and it was found that they are dependent on Ga content. The obtained results enhanced basic understanding and showed that the As–Te–Ga system qualifies for various optoelectronic applications.