Determination and analysis of linear and nonlinear optical properties and electrical conductivity of amorphous Pb_xGe_(42-x)Se_(48)Te_(10) thin films

摘要

Thin films of amorphous Pb_xGe_(42-x)Se_(48)Te_(10) (6≤x≤ 18) have been synthesized by thermal evaporation method on glass substrate. From XRD analysis, it was found that films have an amorphous nature. Different constants (absorption coefficient, a, refractive index, n, extinction coefficient, k, optical energy band gap, E_g, real and imaginary parts of dielectric constants, ε_r and ε_i, as well as energy band tail, E_u) depending on composition were determined by spectrophotometric measurements in wavelength range 200≤λ≤2500 nm. It is found that E_(g1) and E_(g2) increase with increasing Pb content, but E_u decreases with the increase in Pb content. By using Wemple-DiDomenico model, dispersion energy, E_d, energy of effective dispersion oscillator, E_o, dielectric constant at infinite wavelength, ε_∞, and first and third order of moments, (M_(-1)) and (M_(-3)), can be calculated. In addition, N/m* values increase with the increase in Pb concentration. Moreover, optical (σ_(opt)) and electrical (σ_(ele)) conductivity can be derived from optical measurements. Electrical conductivity, σ, was investigated at room temperature, σ decreases with rising Pb concentration and then rises. Electrical properties can be discussed on the basis of Kolobov's proposal of modulation in defect states with the addition of Pb.