Browsing by Subject "Layered crystals"

Now showing 1 - 7 of 7

Open Access
Anharmonic line shift and linewidth of the Raman modes in TlInS2 layered crystals
(John Wiley & Sons Ltd., 2004) Yuksek, N. S.; Gasanly, N. M.; Aydınlı, Atilla
The temperature dependence of the unpolarized Raman spectra from TlInS 2 layered crystal was measured between 10 and 300 K. The analysis of the experimental data showed that the temperature dependences of wavenumbers and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) was found to be due to three-phonon processes. This work demonstrates that the two Raman modes at 280.9 and 292.3 cm-1 exhibit changes toward high wavenumbers as the temperature is raised from 10 to 300 K.
Open Access
Donor - acceptor pair recombination in Tl2InGaS4 layered crystals
(2005) Goksen, K.; Gasanly, N.M.; Ozkan H.; Aydınlı, Atilla
Photoluminescence (PL) spectra of Tl2InGaS4 layered single crystals were studied in the temperature range 15-150 K and wide laser excitation intensity range 0.01-110.34 Wcm-2. We observed a total of three PL bands, one centered at 542 nm (2.286 eV, A-band), one at 607 nm (2.041 eV, B-band), and one at 707 nm (1.754 eV, C-band), at various excitation intensities. The A- and the B-bands were determined to be due to radiative transitions from moderately deep donor levels located at 0.189 and 0.443 eV below the bottom of the conduction band to the shallow acceptor levels at 0.025 and 0.016 eV above the top of the valence band, respectively. The blue shift of the C-band peak energy and the quenching of the PL with increasing temperature are explained within the configuration coordinate model. The observation in the PL spectra of different emission bands in the sequence of B-, C- and A-bands at low, moderate, and high excitation laser intensities, respectively, are attributed to the shift of the quasi-Fermi level with increasing excitation intensity.
Open Access
Infrared photoluminescence from TlGaS2 layered single crystals
(Wiley - V C H Verlag GmbH & Co., 2004) Yuksek, N. S.; Gasanly, N. M.; Aydınlı, Atilla; Ozkan, H.; Acikgoz, M.
Photolimuniscence (PL) spectra of TlGaS2 layered crystals were studied in the wavelength region 500-1400 nm and in the temperature range 15-115 K. We observed three broad bands centered at 568 nm (A-band), 718 nm (B-band) and 1102 nm (C-band) in the PL spectrum. The observed bands have half-widths of 0.221, 0.258 and 0.067 eV for A-, B-, and C-bands, respectively. The increase of the emission band half-width, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature are explained using the configuration coordinate model. We have also studied the variations of emission band intensity versus excitation laser intensity in the range from 0.4 to 19.5 W cm-2. The proposed energy-level diagram allows us to interpret the recombination processes in TlGaS2 crystals.
Open Access
Resonant Raman scattering near the free-to-bound transition in undoped p-GaSe
(Wiley, 2001) Gasanly, N. M.; Aydınlı, A.; Özkan, H.
Raman spectra of GaSe layered crystal have been measured using a He-Ne laser and temperature tuning the free-to-bound gap in the range 10-290 K. Resonance enhancement of E’’(2) mode has been observed for both incident and scattered photon energies equal to the free-to-bound transition energy.
Open Access
Temperature dependence of Raman-active modes of TIGaS2 layered crystals: An anharmonicity study
(Korean Physical Society, 2004) Yuksek, N. S.; Gasanly, N. M.; Ozkan, H.; Aydınlı, Atilla
The temperature dependence (16 - 300 K) of unpolarized Raman spectra from TIGaS2 layered crystals was measured in the frequency range of 10 - 400 cm-1. The analysis of the experimental data showed that the temperature dependencies of the phonon frequencies and linewidths were well described by considering the contributions from thermal expansion and lattice anharmonicity. The anharmonic contribution (phonon-phonon coupling) was found to be due to three-phonon processes. The present work demonstrates that the interlayer Raman mode at 42.6 cm-1 shifts toward high frequency as the temperature is raised from 16 to 300 K.
Open Access
Temperature-dependent Raman scattering spectra of ε-GaSe layered crystal
(Elsevier Science, 2002) Gasanly, N. M.; Aydnl, A.; Özkan, H.; Kocabaş, C.
The temperature dependencies (15-300 K) of seven Raman-active mode frequencies and linewidths in layered gallium selenide have been measured in the frequency range from 10 to 320 cm-1. We observed softening and broadening of the optical phonon lines with increasing temperature. Comparison between the experimental data and theories of the shift and broadening of the intralayer phonon lines during heating of the crystal showed that the experimental dependencies can be explained by the contributions from thermal expansion, lattice anharmonicity and crystal disorder. The pure-temperature contribution (phonon-phonon coupling) is due to three-phonon processes. Moreover, it was established that the effect of crystal disorder on the linewidth broadening of TO mode is stronger than that of LO mode.
Open Access
Thermally stimulated current observation of trapping centers in undoped GaSe layered single crystals
(Wiley, 2001) Gasanly, N. M.; Aydınlı, A.; Salihoglu, Ö.
Undoped p-GaSe layered single crystals were grown using Bridgman technique. Thermally stimulated current measurements in the temperature range of 10-300 K were performed at a heating rate of 0.18 K/s. The analysis of the data revealed three trap levels at 0.02, 0.10 and 0.26 eV. The calculation for these traps yielded 8.8 × 10-27, 1.9 × 10-25, and 3.2 × 10-21 cm2 for capture cross sections and 3.2 × 1014, 1.1 × 1016, and 1.2 × 1016 cm-3 for the concentrations, respectively.