14 results
Search Results
Now showing 1 - 10 of 14
Article Citation - WoS: 4Citation - Scopus: 4Mixed Conduction and Anisotropic Single Oscillator Parameters in Low Dimensional Tlinse2 Crystals(Elsevier Science Sa, 2013) Qasrawi, A. F.; Gasanly, N. M.Due to the importance of the TlInSe2 crystal as neutron and gamma-ray detectors, its electrical and dispersive optical parameters have been investigated. Particularly, the anisotropic current conduction mechanism in the temperature region of 100-350 K and the room temperature anisotropic dispersive optical properties were studied by means of electrical conductivity and optical reflectance, respectively. It has been shown that the mixed conduction is the most dominant transport mechanism in the TlInSe2 crystals. Particularly, when the electric field is applied perpendicular to the crystal's c-axis, the main dominant current transport mechanism is due to the mixed conduction and the variable range hopping above and below 160 K, respectively. When the electric field is applied parallel to the crystal's c-axis, the electrical conductivity is dominated by the thermionic emission, mixed conduction and variable range hopping at high, moderate and low temperatures, respectively. The optical reflectivity analysis in the wavelength range 210-1500 nm revealed a clear anisotropy effect on the dispersive optical parameters. Particularly, the static refractive index, static dielectric constant, dispersion energy and oscillator energy exhibited values of 2.50, 6.24, 20.72 eV and 3.96 eV, and values of 3.05, 9.33, 39.27 eV and 4.72 eV for light propagation parallel and perpendicular to the crystal's c-axis, respectively. Moreover, the frequency dependence of the dielectric constant, epsilon(omega), reflected strong dielectric anisotropy that exhibit maximum epsilon(omega) value of 38.80 and 11.40 at frequencies of 11.07 x 10(14) Hz for light propagation parallel and perpendicular to the crystal's c-axis, respectively. The anisotropy in the epsilon(omega) makes the TlInSe2 crystals attractive to be used as nonvolatile static memory devices. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 28Citation - Scopus: 10Electrical Conductivity and Hall Mobility in P-Type Tlgase2 Crystals(Pergamon-elsevier Science Ltd, 2004) Qasrawi, AF; Qasrawı, Atef Fayez Hasan; Gasanly, NM; Qasrawı, Atef Fayez Hasan; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringSystematic dark electrical conductivity and Hall mobility measurements have been carried out in the temperature range of 200-350 K on p-type TlGaSe2 crystals. The analysis of the temperature-dependent electrical conductivity and carrier concentration reveals the extrinsic type of conduction with an acceptor impurity level located at 0.33 eV, and donor and acceptor concentrations of 9.0 x 10(15) and 1.3 x 10(16) cm(-3), respectively. A hole and electron effective masses of 0.520m(0) and 0.325m(0), respectively, with a donor to acceptor compensating ratio of 0.69 are also being identified. The Hall mobility is found to be limited by the hole-phonon short-range interactions scattering with a hole-phonon coupling constant of 0.17. (C) 2004 Elsevier Ltd. All rights reserved.Article Citation - WoS: 9Citation - Scopus: 9Thermally Stimulated Current Measurements in Undoped Ga3inse4< Single Crystals(Pergamon-elsevier Science Ltd, 2011) Isik, M.; Işık, Mehmet; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringThe trap levels in nominally undoped Ga3InSe4 crystals were investigated in the temperature range of 10-300 K using the thermally stimulated currents technique. The study of trap levels was accomplished by the measurements of current flowing along the c-axis of the crystal. During the experiments we utilized a constant heating rate of 0.8 K/s. Experimental evidence is found for one hole trapping center in the crystal with activation energy of 62 meV. The analysis of the experimental TSC curve gave reasonable results under the model that assumes slow retrapping. The capture cross-section of the trap was determined as 1.0 x 10(-25) cm(2) with concentration of 1.4 x 10(17) cm(-3). (C) 2011 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 7Trapping Centers and Their Distribution in Tl2ga2< Layered Single Crystals(Pergamon-elsevier Science Ltd, 2009) Isik, M.; Gasanly, N. M.Thermally stimulated current (TSC) measurements with current flowing perpendicular to the layers were carried out on Tl2Ga2Se3S layered single crystals in the temperature range of 10-260K. The experimental data were analyzed by using different methods, such as curve fitting, initial rise and isothermal decay methods. The analysis revealed that there were three trapping centers with activation energies of 12, 76 and 177 meV. It was concluded that retrapping in these centers was negligible, which was confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. The capture cross section and the concentration of the traps have been also determined. An exponential distribution of electron traps was revealed from the analysis of the TSC data obtained at different light illumination temperatures. This experimental technique provided values of 10 and 88 meV/decade for the traps distribution related to two different trapping centers. (C) 2009 Elsevier Ltd. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Trap Distribution in Agin5s8< Single Crystals: Thermoluminescence Study(Pergamon-elsevier Science Ltd, 2018) Delice, S.; Işık, Mehmet; Isik, M.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringDistribution of shallow trap levels in AgIn5S8 crystals has been investigated by thermoluminescence (TL) measurements performed below room temperature (10-300 K). One broad TL peak centered at 33 K was observed as constant heating rate of 0.2 K/s was employed for measurement. The peak shape analysis showed that the TL curve could consist of several individual overlapping TL peaks or existence of quasi-continuous distributed traps. Therefore, TL experiments were repeated for different stopping temperatures (T-stop) between 10 and 34 K with constant heating rate of 0.2 K/s to separate the overlapping TL peaks. The E-t vs T-stop indicated that crystal has quasi-continuously distributed traps having activation energies increasing from 13 to 41 meV. Heating rate effect on trapped charge carriers was also investigated by carrying out the TL. experiments with various heating rates between 0.2 and 0.6 K/s for better comprehension of characteristics of existed trap levels. Analyses indicated that the trap levels exhibited the properties of anomalous heating rate behavior which means the TL intensity and area under the TL peak increase with increasing heating rate.Article Citation - Scopus: 1Infrared and Raman Scattering Spectra of Layered Structured Ga3inse4< Crystals(Elsevier Science Bv, 2013) Isik, M.; Gasanly, N. M.; Korkmaz, F.The infrared reflectivity and transmittance and Raman scattering in Ga3InSe4 layered crystals were investigated in the frequency ranges of 100-400, 400-4000 and 25-500 cm(-1). The refractive and absorption indices, the frequencies of transverse and longitudinal optical modes, high- and low-frequency dielectric constants were obtained from the analysis of the IR reflectivity spectra. The bands observed in IR transmittance spectra were interpreted in terms of two-phonon absorption processes. (C) 2012 Elsevier B.V. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Analysis of Optical Constants and Temperature-Dependent Absorption Edge of Gas0.75se0.25< Layered Crystals(Pergamon-elsevier Science Ltd, 2017) Isik, Mehmet; Gasanly, NizamiGaS0.75Se0.25 single crystals were optically characterized through transmission and reflection measurements in the wavelength range of 450-1000 nm. Derivative spectrophotometry analyses on temperature dependent transmittance spectra showed that band gap energies of the crystal increase from 239 eV (T=300 K) to 2.53 eV (T=10 K). Band gap at zero temperature, average phonon energy, electron phonon coupling parameter and rates of change of band gap energy with temperature were found from the temperature dependences of band gap energies under the light of different models reported in literature. Furthermore, the dispersion of room temperature refractive index was discussed in terms of single effective oscillator model. The refractive index dispersion parameters, namely oscillator and dispersion energies, zero-frequency refractive index, were determined as a result of analyses. (C) 2017 Elsevier Ltd. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Trapping Center Parameters in In6s7< Crystals(Elsevier Science Bv, 2011) Isik, M.; Gasanly, N. M.Thermally stimulated current measurements were carried out on In6S7 single crystals in the temperature range of 10-225 K with a constant heating rate of 0.8 K/s. The study of trapping centers was accomplished by the measurements of current flowing along the c-axis of crystals. The analysis of the glow curve according to various methods, such as curve fitting, initial rise and peak shape methods, gives results in good agreement with each other and revealed two trapping centers in In6S7 with activation energies of 157 and 290 meV. Their capture cross sections have been determined as 7.5 x 10(-23) and 7.1 x 10(-20) cm(2),respectively. The good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping has confirmed that retrapping is negligible in these centers. (C) 2011 Elsevier B.V. All rights reserved.Article Citation - WoS: 9Citation - Scopus: 9TL and TSC studies on TlGaSe2 layered single crystals(Elsevier, 2013) Isik, M.; Bulur, E.; Gasanly, N. M.Defects in - as grown - TlGaSe2 layered single crystals were investigated using Thermoluminescence (TL) and Thermally Stimulated Currents (TSC) techniques in the temperature range 10-300 K. TL and TSC curves of samples illuminated using a light with energy greater than the band gap of the material, i.e. blue light (similar to 470 nm) at 10 K, exhibited peaks around 27 and 28 K, respectively, when measured by heating up the samples at a rate of 1 K/s. TL and TSC curves were analyzed to characterize the defects responsible for the peaks. Both TL and TSC peaks were observed to be obeying first order kinetics. Thermal activation energies of the peaks were determined using various methods: curve fitting, initial rise, peak shape and different heating rates. For both TL and TSC peaks, thermal activation energy was determined as around 8 meV, implying that they may originate from similar kinds of trapping centers. A distribution of traps (in terms of energy) was experimentally verified by illuminating the sample at different temperatures and measuring the TL curves. As a result of this, the apparent thermal energies were observed to be shifted from similar to 8 to similar to 17 meV by increasing the illumination temperature from 10 to 16 K. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 4Study on Thermoluminescence of Tlins2 Layered Crystals Doped With Pr(Elsevier Sci Ltd, 2018) Delice, S.; Isik, M.; Gasanly, N. M.Praseodymium (Pr) doped TlInS2 crystals were studied by means of thermoluminescence (TL) measurements performed below room temperature with various heating rates. Detected TL signal exhibited glow curve consisting in overlapping two TL peaks at temperatures of 35 K (peak A) and 48 K (peak B) for 0.6 K/s heating rate. TL curve was analyzed with curve fitting and initial rise methods. Both of the applied methods resulted in consistent activation energies of 19 and 45 meV. The revealed trap levels were found to be dominated by mixed order of kinetics. Various heating rate dependencies of TL glow curves were also investigated and it was found that while peak A shows usual behavior, peak B exhibits anomalous heating rate behavior. Distribution of trap levels was explored using an experimental method called as T-max-T-stop method. Quasi-continuous distributions with increasing activation energies from 19 to 29 meV (peak A) and from 45 to 53 meV (peak B) were ascribed to trap levels. Effect of Pr doping on the TL response of undoped TlInS2 crystals was discussed in the paper.
