Temel Mühendislik Ana Bilim Dalı

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Determination of trapping parameters of Tl2In2S3Se layered single crystal by thermoluminescence
(Wiley, 2018) Güler, İpek; Gasanly, Nizami; 101531
Thermoluminescence (TL) measurements are performed to evaluate the trap states in Tl2In2S3Se layered single crystals. TL experiments are conducted with varying temperature from 10 to 300 K and warming rates from 0.2 to 1.0 K s(-1). From the analysis of both initial rise and curve fitting methods, the activation energy of the traps is obtained as 23 meV. The Chen's method is also used to find activation energy. By means of this technique, the activation energy of the TL glow curve is calculated as 25 meV. From both Chen's method and curve fitting method, the existence of mixed order of kinetics in Tl2In2S3Se crystal is found. The cross section to capture of the trap center is found out from the results of curve fitting method. The trap distribution of the crystals is investigated with different temperatures of illumination at a constant warming rate of 0.8 K s(-1). The temperatures of illumination change from 10 to 22 K. As a result of the increase in temperatures of illumination, the peak maximum values move to higher temperatures and intensity of the TL curves decreases. This behavior shows us that quasicontinuous traps distribution is present in Tl2In2S3Se layered single crystals.
Optical and photoelectrical properties of TlInSSe layered single crystals
(Elsevier GMBH, 2018) Güler, İpek; Gasanly, N.; 101531
Optical and electrical properties of TlInSSe layered single crystals have been studied by means of transmission, reflection and photoconductivity measurements. Transmission and reflection experiments have been carried out from 540 to 1000 nm at room temperature. Derivative analysis was applied to both transmission and reflection spectra and indirect band gap energy was found as 2.06 eV. Photoconductivity measurements have been performed in the temperature range from 245 to 300 K and in the voltage range from 10 to 80 V. From the temperature-dependent photoconductivity measurements, the observed single peak shifted to higher wavelengths with increase of temperature. The increase of photoconductivity with temperature is due to the increase in the mobility of photocarriers that can be explained by Bube model. From X112 method, room temperature indirect band gap of the crystal was also found as 2.06 eV. From voltage-dependent photoconductivity measurements, the peak maximum increased linearly with increase of voltage because of increase of the mobility of charge carriers. Dark current-voltage characteristic of TlInSSe crystal showed the ohmic behavior that means space charge limited current did not exist in the crystal. From the photocurrent with different illumination intensity analysis, the supralinear photoconductivity associated with the two center model was found.
Optical and structural characterization of silicon nitride thin films deposited by PECVD
(Elsevier, 2019) Güler, İpek; 101531
Plasma enhanced chemical vapor deposition (PECVD) technique was used to deposit silicon nitride (SiNx) thin films. The silane (SiH4) and ammonia (NH3) were used as reactant gases. Both the flow rates of the NH3 and SiH4 gases were changed but total flow rate kept constant to obtain the different ratio nitrogen (N) in the SiNx films. Fourier transform infrared spectroscopy (FTIR) was used to get information about absorption ratios of the films and the bond types in the films. The refractive index of the films was obtained from ellipsometry measurements. From FTIR measurements and ellipsometry measurements, refractive index for amorphous silicon (Si) and refractive index for stoichiometric SiNx were found as 3.27 and 1.91, respectively. The photoluminescence (PL) measurements were used to see the luminescent of the amorphous Si nanoparticles which were occurred spontaneously during deposition process. High resolution transmission electron microscopy (HRTEM) was used to analyze the Si nanoparticle size.
Structural and Optical Properties of Ga2Se3 Crystals by Spectroscopic Ellipsometry
(Springer, 2019) Güler, İpek; Işık, Mesut; Gasanly, Nizami Mamed; Gasanova, L. G.; Babayeva, Raziye; 101531
Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.
Study of vibrational modes in (Ga2S3)(x) - (Ga2Se3)(1-x) mixed crystals by Raman and infrared reflection measurements
(Elsevier, 2019) Güler, İpek; Güler, İpek; Gasanly, Nizami Mamed; 101531
Raman and infrared (IR) reflection characteristics were investigated in the frequency region of 100-450 cm(-1) for (Ga2S3)(x) - (Ga2Se3)(1-x) mixed crystals for compositions of x increasing from 0.0 to 1.0 by intervals of 0.25 obtained by Bridgman crystal growth technique. In the Raman spectra of these crystals four dominant peak features were observed while two bands were detected in the IR spectra of interest samples. Kramers-Kronig dispersion relations applied to IR spectra presented the frequencies of transverse optical modes. The compositional dependencies of revealed Raman- and IR-active mode frequencies on (Ga2S3)(x) - (Ga2Se3)(1-x) crystals were established. One-mode behavior was displayed from indicated dependencies.

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