A. Ateş

Morphological, optical and electrical properties of CdZnO films prepared by sol–gel method

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.

Nonlinear and saturable absorption characteristics of amorphous InSe thin films

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 wit...

Electric field influence on absorption measurement in InSe single crystal

Abstract InSe single crystal was grown by Bridgman–Stockberger method. Electric field effect on the absorption measurements have been investigated as a function temperature in InSe single crystal. The absorption edge shifted towards longer wavelengths and a decrease of intensity in absorption spectra occurred under an electric field of 5 kV / cm . Using absorption measurements, steepness parameter and Urbach energy were calculated under electric field. Applied electric field caused an increase in the Urbach energy. At 10 and 320 K , the first exciton energies were calculated as 1.350 and 1.311 eV for zero voltage and 1.334 and 1.301 eV for electric field respectively.

The effect of thickness and/or doping on the nonlinear and saturable absorption behaviors in amorphous GaSe thin films

We 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 fre...

IN SITU OPTICAL ASSESSMENT OF SEMI-INSULATING IRON DOPED INP GROWN BY LIQUID ENCAPSULATED CZOCHRALSKI PROCESS

In semi-insulating, Fe doped InP, we demonstrate that infrared absorption technique provides quantitative measurements of Fe concentrations. We show that the quantum efficiency is reduced more than 70% in Fe doped samples, in comparison to undoped samples. Relative near band edge photoluminescence (PL) intensity is antiproportional to Fe concentration. This can provide a calibration method to transform scanning PL images to quantitative Fe distributions. We demonstrate that infrared absorption mapping images Fe distribution in InP, in a similar way to EL2 imaging in GaAs. The images show that the slip-like defects decorated by Fe centers predominantly lie along [011] direction.

Absorption measurements in InSe:Ho single crystal under an electric field

InSe:Ho single crystal was grown by Bridgman-Stockberger method. Electric field effects on the absorption measurements have been investigated as a function of temperature in InSe:Ho single crystal. The absorption edge shifted towards longer wavelengths and a decrease of intensity in absorption spectra occurred under an electric field of 7.5 kV/cm. Using absorption measurements, steepness parameter and Urbach energy were calculated under electric field. Applied electric field caused an increase in the Urbach energy. At 10 K and 320 K, the first exciton energies were calculated as 1.322 and 1.301 eV for zero voltage and 1.245 and 1.232 eV for applied electric field, respectively.

The Growth of P-type TlGaSe2(1−x) S2x Single Crystals

TlGaSe2(1−x) S2x single crystals were grown by the modified Bridgman-Stockbarger method in our crystal growth laboratory. AIIIBIII C2VI compounds are formed of elements from vertical groups of the periodic table (group III: Tl, Ga, In; group VI: Se, S, Te) and are classified into two types. The first type has a layer structure: TlGaSe2, TlGaS2 and TlInS2. The second type has a chained structure: TlInSe2, TlInTe2 and TlGaTe2. None of the grown crystals had cracks and voids on the surface. The freshly cleaved crystals had a mirror-like surface and there was no need for mechanical or chemical polishing treatments. By the hot probe technique, we have found that the crystals were of p-type. The ingots produced were single crystalline and the useful region of single crystal was 90% with steps of 10 K if changes were small, and with steps of 3 and 5 K if changes were large in the direct and indirect band gaps energies. The direct and indirect band gaps for TlGaSe2(1−x)S2x samples were calculated as a function of temperature.

Modification of exciton binding energy in the horizontal Bridgman–Stockbarger growth of InSe by Ho doping

Undoped InSe and Ho doped InSe single crystals with various Ho concentrations were grown by the horizontal Bridgman-Stockbarger method. The absorption measurements were carried out in the temperature range 10–320K. Exciton binding energies, steepness parameters, and Urbach energies of InSe and InSe:Ho samples were investigated as a function of temperature. Ho doping caused a shift towards longer wavelengths in the absorption edge. In general, Ho doping causes certain increases in the exciton binding energy and Urbach energy, and a decrease in the steepness parameter. An enhancement of exciton binding energy up to about 55meV is observed at 0.0025 mass ratio of Ho.

Growth, Optical and Electirical Properties of In2S3, In1−xCdxS and CdS Thin Films by the (SILAR) Method

In2S3 and In1−xCdxS and CdS thin films were grown on glass substrates by using Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature. The band gap energies of the films were determined by optical absorption measurements. The optical absorption measurements were done as a function of the in the 10–320 K temperature range. It has been seen that, the band gap energies of the In2S3, In1−xCdxS and CdS are decreasing with in increasing temperature. The electrical characterization was done by current‐voltage measurements with two probe method. The electrical resistivity measurements were done as a function of the in the 300–450 K temperature range. The electrical resistivity are decreasing with in increasing temperature. The resistivity were calculated at 300 K and 450 K, as 2×106 Ωcm and 1×104 Ωcm, 1,5×107 and 5,4×103, 1,5×107 and 1,2×104 Ωcm for CdS, In1−xCdxS, In2S3, respectively.

The effect of thickness and doping on the nonlinear absorption behaviour of IIIA-VIA group amorphous semiconductor thin films

The nonlinear optical absorption of InSe, GaSe and GaxIn1−xSe amorphous films with varying thickness and doping has been studied by open-aperture Z-scan experiment with 4 ns and 65 ps pulse durations at 1064 nm wavelength and femtosecond pump-probe spectroscopy. Our results show that the dopant and film thickness (from 20 nm to 104 nm) results in switching from saturable absorption to nonlinear absorption for equal input intensities. This behaviour is attributed to increasing localized defect states with increasing film thickness and/or dopant. The experimental curves were fitted to the theory of open aperture Gaussian beam Z-scan based on the Adomian decomposition method incorporating one photon, two photon, and free carrier absorptions and their saturations. By preparing very thin amorphous thin films the saturation threshold has been lowered significantly.