Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 3Citation - Scopus: 3Local Vibrational Modes of Natural Isotopes of Substitutional Oxygen in Cdte(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2020) Tarhan, Enver; Ramdas, Anant K.We investigated the localized vibrational modes (LVM) of natural oxygen containing ${}^{16}O,\;{}^{17}O$ and ${}^{18}O$ isotopes at a substitutional tellurium site in cadmium telluride using infrared absorption spectroscopy at cryogenic temperatures. The main absorption peak observed at 350 cm ?1 was formerly attributed to a fundamental LVM mode (?0) of oxygen at a tellurium site. The relatively weak absorption peaks observed at 331 $cm^{-1}$ and 340 $cm^{-1}$ are assigned as the same $\nu_0$ mode of the ${}^{17}O$ and ${}^{18}O$ isotopes, respectively, based on their relative intensities and spectral positions. The spectral positions were confirmed with theoretical calculations using a linear chain model where the peak position at 350$cm^{-1}$ was taken as the reference for the ${}^{16}O$ isotope. From a least square analysis of the observed peak positions we were able to calculate the force constants from perturbation theory. A Lorentzian line shape analysis of each $\nu_0$ absorption peak, considering the effects of isotopic mass and natural abundance variations of the host Cd atoms, was also carried out to further confirm their assignments. Reasonably good line shape fittings were obtained for $\nu_0$ modes of all isotopes of oxygen.Article Citation - WoS: 6Citation - Scopus: 10Effect of Annealing on the Density of Defects in Epitaxial Cdte (211)/Gaas(Springer, 2018) Bakali, Emine; Selamet, Yusuf; Tarhan, EnverCdTe thin films were grown on GaAs (211) wafers by molecular beam epitaxy as the buffer layer for HgCdTe infrared detector applications. We studied the effect of annealing on the density of dislocation of these CdTe thin films under varying annealing parameters such as annealing temperature, annealing duration, and number of cycles. Annealings were carried out using a homemade annealing reactor possessing a special heater element made of a Si wafer for rapid heating. The density of dislocations, which were made observable with a scanning electron microscope after etching with an Everson solution, were calculated by counting the number of dislocations per unit surface area, hence the term etch pit density (EPD). We were able to decrease EPD values by one order of magnitude after annealing. For example, the best EPD value after a 20-min annealing at 400°C was ∼ 2 × 107 cm−2 for a 1.63-μm CdTe thin film which was about 9.5 × 107 cm−2 before annealing. We also employed Raman scattering measurements to see the changes in the structural quality of the samples. From the Raman measurements, we were able to see improvements in the quality of our samples from the annealing by studying the ratio of 2LO/LO phonon mode Raman intensities. We also observed a clear decrease in the intensity of Te precipitations-related modes, indicating a decrease in the size and number of these precipitations.