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We prepared very thin amorphous InSe films and investigated the thickness dependence of the nonlinear absorption by pump-probe and open aperture Z-scan techniques. While thinner films (20 and 52 nm) exhibit saturable absorption, thicker films (70 and 104 nm) exhibit nonlinear absorption for 4 ns, 65 ps, and 44 fs pulse durations. This behavior is attributed to increasing localized defect states in the energy band gap as the film thickness increases. We developed a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations to derive the transmission in the open aperture Z-scan experiment. The theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method was used to fit the experimental curves. Nonlinear absorption coefficients along with saturation intensity thresholds were extracted from fitting the experimental results for all pulse durations. The lowest saturation threshold was found about 3×10−3 GW/cm2 for 20 nm film thickness with nanosecond pulse duration and increased about four orders of magnitude for 104 nm film thickness.

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CdZnO films were deposited by the sol–gel spin coating method onto glass substrates. ZnO, Cd(0.25)Zn(0.75)O, Cd(0.50)Zn(0.50)O, Cd(0.75)Zn(0.25)O, CdO films were deposited using different rates of cadmium acetate dehydrate and zinc acetate dehydrate solutions. These values in parentheses refer to the ratio in solution. The dried and annealing temperatures were selected to be 300 °C and 500 °C in air, respectively. The XRD patterns show polycrystalline nature. It was observed that the crystal structure changes from wurtzite (ZnO) to cubic (CdO) depending on the Zn and Cd proportions in the CdZnO structure. The optical properties of these films have been investigated by means of the optical transmittance measurement. The absorption band edges of films shift from 3.26 to 2.31 eV. The morphological characterizations of the films have been performed by SEM and AFM. In particular, the clusters formed from the nanostructured particles were shown in the SEM image of the Cd(0.75)Zn(0.25)O film. The electrical measurements show that the CdZnO films have semiconducting behaviour and are very sensitive to light.

Articles you may be interested inImpacts of Si-doping and resultant cation vacancy formation on the luminescence dynamics for the near-bandedge emission of Al0.6Ga0.4N films grown on AlN templates by metalorganic vapor phase epitaxyWe investigated the nonlinear and saturable absorption characteristics of very thin amorphous undoped GaSe, Ge ͑0.01 at. %͒, and Sn ͑0.5 at. %͒ doped GaSe films by pump-probe and open aperture Z-scan techniques. Linear absorption measurements indicate blueshift in energy with increasing film thickness. Thinner films exhibit saturable absorption while thicker films exhibit nonlinear absorption for 4 ns and 65 ps pulse durations. The films exhibit competing effects between nonlinear and saturable absorption. Saturable absorption behavior weakens while nonlinear absorption appears with increasing film thickness. In addition to that, saturable absorption behavior is very sensitive to doping. Doping causes absorption behaviors to appear in thinner films compared to undoped films. These behaviors are attributed to increasing localized defect states with increasing film thickness and doping. To derive the transmission in open aperture Z-scan data, a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations were considered. The experimental curves were fitted to the theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method. Nonlinear absorption coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results for both pulse durations used for the experiments. Saturation intensity threshold values increased with increasing film thickness and doping. The lowest saturation intensity threshold for undoped GaSe film was found to be 1.9ϫ 10 −3 GW/ cm 2 for 45 nm film thickness and increased about two orders of magnitude for 74 nm film thickness.