Ortak Dersler Bölümü

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Characterization of linear and nonlinear optical properties of NaBi(WO4)2 crystal by spectroscopic ellipsometry
(2024) Güler, İpek; Güler, İpek; Gasanly, N. M.; 101531
NaBi(WO4)2 compound has been a material of considerable attention in optoelectronic applications. The present research, in which we examined the linear and nonlinear optical properties of NaBi(WO4)2 crystal using the spectroscopic ellipsometry method, elucidates the optical behavior of the crystal in detail. Our work provides a sensitive approach to determine the spectral characteristic of the crystal. The spectral dependence of various optical parameters such as refractive index, extinction coefficient, dielectric function and absorption coefficient was reported in the range of 1.2-5.0 eV. Optical values such as bandgap energy, critical point energy, single oscillator parameters were obtained as a result of the analyses. In addition to linear optical properties, we also investigated the nonlinear optical behavior of NaBi(WO4)2 and shed new light on the potential applications of the crystal. Absorbance and photoluminescence spectra of the crystal were also reported to characterize optical, electronic and emission behavior of the compound. Our findings may form the basis for a number of technological applications such as optoelectronic devices, frequency conversion, and optical sensors. This research contributes to a better understanding of the optical properties of NaBi(WO4)2 crystal, highlighting the material's role in future optical and electronic technologies.
Characterization of N Rich-Silicon Nitride Thin Films Deposited by PECVD
(2023) Güler, İpek; 101531
Silicon nitride thin films are very important for their possible use in semiconductor industry and electronic applications. Changing the deposition parameters, silicon nitrides which have many varying optical properties can be produced. In this work, silicon nitride (SiNx) thin films were deposited on silicon substrates using Plasma enhanced chemical vapor deposition (PECVD) technique. The silane (SiH4) and ammonia (NH3) were used as reactant gases. Using these reactant gases, nitrogen (N) rich SiNx films were obtained. In order to get information about absorption and bond types in the films, films were analyzed by the help of Fourier transform infrared spectroscopy (FTIR) was performed. The refractive index, extinction coefficient and band gap energy of the films were changed from 1.86, 0 and 5.38 eV to 2.05, 0.0048 and 4.26 eV, respectively. Using the refractive index, composition of the films were estimated that is [N]/[Si] ratio of the films varied from 1.38 to 1.62. For possible applications of the SiNx films, learning the origin of the light-emission of the films is very important so the photoluminescence (PL) measurements were also used to see the luminescent of the SiNx films which is related to the electronic transitions between the K-center level and the conduction band tail states.
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.
Exploring the linear and nonlinear optical behavior of (TlInS2)0.75(TlInSe2)0.25: Insights from ellipsometry measurements
(2023) Güler, İpek; Güler, İpek; Gasanly, N.; 101531
The search for layered structured new semiconductor materials with remarkable optical properties has become a driving force, especially for materials science. Tl2In2S3Se [(TlInS2)0.75(TlInSe2)0.25], a fascinating compound, holds great promise for advanced photonic and optoelectronic applications. In the present study, the linear and nonlinear optical properties of Tl2In2S3Se layered single crystals were studied by ellipsometry measurements. The variation of refractive index, extinction coefficient, absorption coefficient and skin depth with energy were investigated. Applying the derivative analysis technique to the absorption spectrum, indirect bandgap was found as 2.19 eV. The refractive index data was analyzed considering single-effective-oscillator model. The lattice dielectric constant, plasma frequency, carrier density to the effective mass ratio and zero-frequency refractive index were found. Moreover, the change in optical conductivity with energy yielded to determine the direct bandgap as 2.40 eV. The optical parameters of nonlinear refractive index, first-and third-order nonlinear susceptibilities were also reported.
Growth and characterization of NaBi(Mo0.5W0.5O4)2 single crystal: A promising material for optoelectronic applications
(2023) Işık, M.; Güler, İ.; Gasanly, N.M.; 101531
The structural and optical characteristics of NaBi(Mo0.5W0.5O4)2 single crystals grown by Czochralski method were investigated. X-ray diffraction (XRD) pattern exhibited four well-defined peaks related to tetragonal crystalline structure with a space group I41/a. Raman and infrared transmittance spectra were recorded to investigate vibrational properties of the compound. Room temperature transmission spectrum was measured to reveal band gap energy of the crystal. The derivative spectral and absorption coefficient analyses resulted in direct band gap energy of 3.19 and 3.18 eV, respectively. Urbach energy of the crystal was also determined as 0.17 eV from photon energy dependency of absorption coefficient. The structural and optical parameters obtained for NaBi(Mo0.5W0.5O4)2 were compared with the parameters of the NaBi(XO4)2 (X: Mo,W) compounds to understand the effect of the composition on the studied properties. The reported characteristics of NaBi(Mo0.5W0.5O4)2 point out that the compound has significant potential to be used in optoelectronic devices.
Growth and temperature tuned band gap characteristics of NaBi(MoO4)2 single crystal
(2023) Isik, M.; Güler, İ.; Gasanly, N.M.; 101531
Structural and optical properties of double sodium-bismuth molybdate NaBi(MoO4)2 semiconductor compound was investigated by x-ray diffraction, Raman and transmission experiments. From the x-ray diffraction experiments, the crystal that has tetragonal structure was obtained. Vibrational modes of the crystal were found from the Raman experiments. Transmission experiments were performed in the temperature range of 10-300 K. Derivative spectroscopy analysis and absorption spectrum analysis were performed to get information about the change in band gap energy of the crystal with temperature. It was observed that the band gap energies of the crystal at different temperatures obtained from these techniques are well consisted with each other. By the help of absorption spectrum which was obtained from transmission measurements performed at varying temperatures, absolute zero value of the band gap and average phonon energy as 3.03 ± 0.02 eV and E p h = 24 ± 0.2 meV, respectively. Moreover, based on absorption spectrum analysis the Urbach energy of the crystal was obtained as 0.10 eV.
Optical analysis of TlInS2xSe2(1-x) mixed crystals
(2014) Güler, İpek; 101531
The ellipsometry measurements were carried out on TlInS2xSe2(1-x) mixed crystals in the spectral range of 1.5-6.0 eV at room temperature. The refractive index, extinction coefficient, real and imaginary parts of dielectric function were found as a result of ellipsometric measurements. The energies of interband transitions (critical point energies) of the TlInS2xSe2(1-x) mixed crystals were obtained by means of the second derivative of the real and imaginary parts of dielectric function. The variation of the critical point energies with the isomorphic anion substitution that is sulfur for selenium atoms was established.
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.
Optical characterization of (TlInS2)0.5(TlInSe2)0.5 crystal by ellipsometry: linear and optical constants for optoelectronic devices
(2023) Guler, İ.; Isik, M.; Gasanly, N.; 101531
TlInSSe [(TlInS2)0.5(TlInSe2)0.5] crystals have garnered significant attention as promising candidates for optoelectronic applications due to their exceptional optoelectrical characteristics. This study focused on investigating the linear and nonlinear optical properties of TlInSSe layered single crystals through ellipsometry measurements. The X-ray diffraction analysis revealed the presence of four distinct peaks corresponding to a monoclinic crystalline structure. In-depth analysis was conducted to examine the variations of refractive index, extinction coefficient, and complex dielectric function within the energy range of 1.25–6.15 eV. By employing derivative analysis of the absorption coefficient and utilizing the Tauc relation, the indirect and direct bandgap energies of TlInSSe crystals were determined to be 2.09 and 2.26 eV, respectively. Furthermore, this research paper presents findings on oscillator energy, dispersion energy, Urbach energy, zero and high frequency dielectric constants, plasma frequency, carrier density to effective mass ratio, nonlinear refractive index, and first-order and third-order nonlinear susceptibilities of TlInSSe crystals.
Spectroscopic ellipsometry studies of optical properties of TlIn(S0.25Se0.75)2 crystal
(2023) Güler, I.; Işık, M.; Gasanly, N.; 101531
The optical properties of TlIn(S0.25Se0.75)2 crystals were studied by ellipsometry measurements. X-ray diffraction pattern presented well-defined peaks associated with monoclinic structure. Energy dependent graphs of various linear optical parameters of the crystal were presented in the 1.25–4.50 eV range. The band gap and Urbach energies of the compound were found as 1.96 and 0.68 eV, respectively, from the analyses of the absorption coefficient. Refractive index spectrum was analyzed considering the single-effective-oscillator model to get oscillator and dispersion energies, zero and high frequency dielectric constants, plasma frequency. Moreover, the nonlinear refractive index, first-order and third-order nonlinear susceptibilities of TlIn(S0.25Se0.75)2 crystal were revealed in the present paper.
Structural and optical properties of (TlInS2)0.75(TlInSe2)0.25 thin films deposited by thermal evaporation
(2023) Güler, I.; Işık, M.; Gasanly, N.; 101531
Layered semiconductor materials have become a serious research topic in recent years, thanks to their effective optical properties. In this article, the thin-film structure of Tl2In2S3Se [(TlInS2)0.75(TlInSe2)0.25] material with layered structure was grown by thermal evaporation method. The structural, morphological, and optical properties of the deposited thin films were examined. X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM) techniques were used to get information about structural and morphological properties of the thin films. XRD pattern presented well-defined peaks associated with monoclinic crystalline structure. The crystallite size, dislocation density, and lattice strain of the films were also obtained from the analyses of XRD pattern. EDS analysis showed that atomic compositional ratios of the Tl, In, S, and Se elements are consistent with chemical formula of Tl2In2S3Se. The optical characterization of thin film was performed using transmission and Raman spectroscopy techniques. Raman spectrum offered information about the vibrational modes of the thin film. The analyses of the transmission spectrum presented the indirect and direct band gap energies of the Tl2In2S3Se thin film as 2.23 and 2.52 eV, respectively. The further analyses on the absorption coefficient resulted in Urbach energy of 0.58 eV.
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.
Structural and optical properties of thermally annealed thallium indium disulfide thin films
(2020) Güler, İpek; Gasanly, N.; 101531
Structural and optical properties of thallium indium disulfide (TlInS2) thin films, deposited by thermal evaporation technique and thermally annealed at different temperatures, were analyzed. Crystallite size, dislocation density and lattice strain of the thin films were found from X-ray diffraction experiments. The atomic compositions of the films were determined from energy dispersive spectroscopy analysis. Surface morphology of the films was analyzed using atomic force microscopy. From room temperature transmittance spectrum, the band gap energies of the films were identified. The decrease in band gap energies of the films with the annealing temperature up to 300 degrees C was observed due to increase in crystallite size and decrease in lattice strain. From Raman measurements, it was observed that the Raman shifts of the films were well correlated with those of TlInS2 bulk crystal.
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.
Temperature and Excitation Intensity Tuned Photoluminescence In Ga0.75In0.25Se Crystals
(Elsevier Science BV, 2013) Işık, M.; Güler, I.; Gasanlyc, N. M.; 101531
Photoluminescence (PL) spectra of Ga0.75In0.25Se layered single crystals have been studied in the wavelength range of 580-670 nm and temperature range of 7-59 K. Two PL emission bands centered at 613 nm (2.02 eV, A-band) and 623 nm (1.99 eV, B-band) were revealed at T = 7K. The excitation laser intensity dependence of the emission bands have been studied in the 0.06-1.40 W cm(-2) range. Radiative transitions from shallow donor levels located at E-A = 0.11 and E-B = 0.15 eV below the bottom of conduction band to single shallow acceptor level located at 0.01 eV above the valence band are suggested to be responsible for the observed A- and B-bands. A simple model was proposed to interpret the recombination processes in Ga0.75In0.25Se single crystals. (c) 2012 Elsevier B.V. All rights reserved.
Temperature-dependent absorption edge and photoconductivity of Tl 2In2S3Se layered single crystals
(2013) Güler, İpek; Ambrico, M.; Ligonzo, T.; Gasanly, N.M.; 101531
Temperature variation of indirect band gap of Tl2In 2S3Se layered single crystals were obtained by means of absorption and photoconductivity measurements. The temperature coefficient of -7.1 × 10-4 eV/K from absorption measurements in the temperature range of 10-300 K in the wavelength range of 520-1100 nm and -5.0 × 10-4 eV/K from PC measurements in the temperature range of 132-291 K in the wavelength range of 443-620 nm upon supplying voltage V = 80 V were obtained. From the analysis of dark conductivity measurements in the temperature range of 150-300 K, conductivity activation energy was obtained as 0.51 eV above 242 K. The degree of the disorder, the density of localized states near Fermi level, the average hopping distance and average hopping energy of Tl2In2S3Se crystals were found as, 1.9 × 105 K, Nf = 4 × 1020 cm -3eV-1, 29.1 Å and 24.2 meV in the temperature range of 171-237 K, respectively. Activation energy of hopping conductivity at T = 171 K was obtained as 41.3 meV and the concentration of trapping states was found as 1.6 × 1019 cm-3.
Thermoluminescence characterization of (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystal compounds
(2020) Güler, İpek; Güler, İpek; Gasanly, N. M.; 101531
Ga2Se3 and Ga2S3 compounds take attention due to their potential applications in photovoltaics. Defects and impurities may affect the quality of optoelectronic devices. Therefore, it is worthwhile to determine the parameters (activation energy, order of kinetics, frequency factor) of traps associated with the defects and/or impurities. The aim of the present paper is to investigate the trapping parameters of (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystal which is one of the member of (Ga2Se3)(x) - (Ga2S3)(1-x) mixed crystals. For this purpose, thermoluminescence (TL) experiments were performed on (Ga2Se3)(0.25) - (Ga2S3)(0.75) single crystals in the 10-300 K region. TL spectra were also recorded using various heating rates in between 0.2 and 1.0 K/s and stopping temperatures from 30 to 60 K to get the detailed information about the characteristics of the trapping parameters. TL glow curves exhibited the overlapped peaks. The stopping temperature experimental data indicated that traps present quasi-continuous distribution within the band gap. Initial rise method analyses were applied to get the activation energies of quasi-continuously distributed revealed traps. Thermal activation energies of distributed traps were found as increasing from 108 to 246 meV as stopping temperature was increased from 30 to 60 K. The structural characteristics (lattice constants and atomic compositions of constituent elements) of used compound were also reported in the present study.

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