The effect of Ga/In ratio and annealing temperature on the nonlinear absorption behaviors in amorphous TlGaxIn(1-x)S2 (0 ≤ x ≤ 1) chalcogenide thin films

Abstract

The amorphous semiconductor TlGaxIn(1-x)S2 (0 ≤ x ≤ 1) chalcogenide thin films were prepared with 70 nm thicknesses by using vacuum evaporation technique. The nonlinear absorption properties of the films were studied by Z-scan technique. The energy band gap values were calculated by using linear absorption spectra. The effect of Ga/In ratio leads to increase 0.22 eV in band gap energy. To derive the transmission in open aperture Z-scan data, a theoretical model incorporating two photon and free carrier absorptions and their saturations were considered and effective nonlinear absorption coefficients and saturation intensity thresholds extracted from the fitting of the experimental results. Highest effective nonlinear absorption coefficient was found for TlInS2 sample due to having the smallest energy bandgap. In an attempt to investigate the effect of localized defect states on the nonlinear absorption, TlGaS2 thin films were annealed up to 473 K. It was found that increasing annealing temperature leads to reduction of the localized defect states. Nonlinear absorption coefficient and saturation intensity threshold decrease with reduction of the localized defect states.