Optical and electrical transport properties of some quaternary thallium dichalcogenides

Güler, İpek
In this thesis, in order to study the structural, optical and electrical transport properties of Tl2In2S3Se, TlInSeS and Tl2In2SSe3 crystals, X-ray diffraction (XRD), energy dispersive spectroscopic analysis (EDSA), transmission, reflection, photoluminescence (PL), thermally stimulated current (TSC) and photoconductivity decay (PC) measurements were carried out. Lattice parameters and atomic composition of these crystals were determined from XRD and EDSA experiments, respectively. By the help of transmission and reflection experiments, the room temperature absorption data were analyzed and it was revealed the coexistence of indirect and direct band gap energies of the studied crystals. Moreover, the refractive index dispersion parameters - oscillator energies, dispersion energies, oscillator strengths, oscillator wavelengths and zero-frequency refractive indexes were determined. Temperature-dependent transmission measurements made it possible to find the rate of change of indirect band gaps with temperature, absolute zero values of the band gap energies and Debye temperatures of these crystals. From the analysis of the transmission and reflection measurements, it was established that, there is a decrease in the values of indirect and direct band gaps energies and an increase in zero-frequency refractive indexes with increasing of selenium content. PL measurements were carried out to obtain the detailed information about recombination levels in crystals studied. The behavior of PL spectra were investigated as a function of laser excitation intensity and temperature. The variation of the spectra with laser excitation intensity and temperature suggested that the observed emission bands in these crystals were due to the donor-acceptor pair recombination. TSC measurements were carried out with various heating rates at different illumination temperatures to obtain information about trap levels in these crystals. The mean activation energies, attempt-to-escape frequencies, concentrations and capture cross sections of the traps were determined as a result of TSC spectra analysis. The analysis of experimental TSC curves registered at different light illumination temperatures revealed the exponential trap distribution in the studied crystals. From the analysis of PC measurements, carrier lifetimes were obtained.


Optical and photoelectrical properties of TlInSSe layered single crystals
Güler, Işıkhan; Hasanlı, Nızamı (2018-01-01)
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 fro...
Optical properties of TlGaSeS layered single crystals
Güler, Işıkhan; Hasanlı, Nızamı (2007-12-01)
The optical properties of TlGaSeS layered single crystals have been investigated by measuring the transmissions and the reflections in the wavelength region between 400 and 1100 nm. The optical indirect transitions with a band gap energy of 2.27 eV and direct transitions with a band gap energy of 2.58 eV were found by means of the analysis of the absorption data at the room temperature. The rate of change of the indirect band gap with temperature, that is, gamma = -3.2 x 10(-4) eV/K, was determined from the...
Optical and Vibrational Properties of [Pt@Pb-12](2-), [Ni@Pb-12](2-), and [Ni@Pb-10](2-) Zintl Ion Clusters
Çetin, Asude; Esentürk, Okan; Nalbant Esentürk, Emren (Wiley, 2017-05-10)
The optical and vibrational properties of Pt- and Ni-centered Pb-Zintl-ion clusters have been investigated by UV/Vis and FTIR spectroscopy. Computational studies have been performed to better interpret the experimental data, due to a lack of any FTIR and UV/Vis spectroscopic studies on these clusters or similar ones in the literature. UV/Vis spectroscopic analyses show an asymmetric broad absorption band, with a maximum at 265 nm for both Pt- and Ni-centered Pb clusters. FTIR spectroscopic analysis demonstr...
Optical properties of GaS crystals: Combined study of temperature-dependent band gap energy and oscillator parameters
IŞIK, MEHMET; TUĞAY, EVRİN; Hasanlı, Nızamı (2017-08-01)
Optical parameters of gallium sulfide (GaS) layered single crystals have been found through temperature-dependent transmission and room temperature reflection experiments in the wavelength range of 400-1100 nm. Experimental data demonstrates the coexistence of both optical indirect and direct transitions and the shift of the absorption edges toward lower energies by increasing temperature in the range of 10-300 K. Band gap at zero temperature, average phonon energy and electron phonon coupling parameter for...
Optical properties of (Ga2Se3)(0.)(75) - (Ga2S3)(0.)(25) single crystals by spectroscopic ellipsometry
Işık, Mehmet; Hasanlı, Nızamı; Gasanova, L. (Elsevier BV, 2019-05-01)
Structural and optical properties of 75 mol % Ga2Se3 - 25 mol % Ga2S3 system of single crystals were investigated by experimental techniques of x-ray diffraction (XRD), energy dispersive spectroscopy, Raman spectroscopy and ellipsometry. XRD pattern indicated that the studied compound has crystalline nature with cubic structure. Vibrational modes in the crystal were revealed using Raman spectroscopy experiments in the 90-450 cm(-1) frequency range and nine modes were observed in the spectrum. Ellipsometry m...
Citation Formats
İ. Güler, “Optical and electrical transport properties of some quaternary thallium dichalcogenides,” Ph.D. - Doctoral Program, Middle East Technical University, 2011.