Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Other Erratum To: Mbe-Grown Cdte Layers on Gaas With In-Assisted Thermal Deoxidation(Springer Verlag, 2016) Arı, Ozan; Bilgilisoy, Elif; Özçeri, Elif; Selamet, YusufArticle Citation - WoS: 6Citation - Scopus: 5Mbe-Grown Cdte Layers on Gaas With In-Assisted Thermal Deoxidation(Springer Verlag, 2016) Arı, Ozan; Bilgilisoy, Elif; Özçeri, Elif; Selamet, YusufMolecular beam epitaxy (MBE) growth of thin (∼2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm−2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.Article Citation - WoS: 11Citation - Scopus: 12Characterization of Cdte Growth on Gaas Using Different Etching Techniques(Springer Verlag, 2015) Bilgilisoy, Elif; Özden, Selin; Bakali, Emine; Karakaya, Merve; Selamet, YusufCdTe buffer layers which were grown on (211)B GaAs by molecular beam epitaxy were subjected to two different etch treatments to quantify the crystal quality and dislocation density. The optical properties and thicknesses of the samples were obtained by ex situ spectroscopic ellipsometry. The surface morphologies of the CdTe epilayers were analyzed by atomic force microscopy, scanning electron microscopy, and Nomarski microscopy before and after chemical etching. We compare the triangle- and trapezoid-shaped etch pits due to the Everson and Nakagawa etch solutions, respectively. Measured etch pit density (EPD) values of triangle etch pits were found in the 8 × 107 cm−2 to 2 × 108 cm−2 range, and trapezoid-shaped etch pits were found in the 1 × 107 cm−2 to 7 × 107 cm−2 range for samples with thicknesses <2 μm.Article Citation - WoS: 10Citation - Scopus: 10Carbon Nanotube Diameter Tuning Using Hydrogen Amount and Temperature on Sio2/Si Substrates(Springer Verlag, 2010) Aksak, Meral; Selamet, YusufCarbon nanotubes (CNTs) were grown on thin iron (Fe) films on SiO 2/Si substrates by chemical vapor deposition (CVD) at four different hydrogen (H2)/methane (CH4) ratios at temperatures ranging from 925 to 1000°C. The effects of temperature and the amount of hydrogen gas on the mean diameter at increasing temperature were examined. We demonstrated that the mean diameter and its distribution depend not only on temperature but also on the H2 amount. We showed that increasing H2 amount strongly affects the structure of CNTs, especially at high growth temperature; the mean diameter at 1000°C reduced from about 383 to 34 nm by increasing H2 amount from 24 to 50 sccm. We observed that at high temperature growth the mean diameter was decreasing very fast initially with increasing H2 amount suggesting the dominance of H2 over the growth temperature. A decrease in the slope of diameter vs. H 2 amount with further increment in H2 amount implied that the temperature was, then, deciding the CNT diameter through catalyst particle coarsening. The statistical analysis presented implies that the H2 amount has to be adjusted according to the growth temperature for given CH 4 amount to keep CNT diameter under control, and the large diameter distributions at high temperature and high H2 amount can be associated with the large variation in the catalyst particle sizes. © 2010 Springer-Verlag.Article Citation - WoS: 89Citation - Scopus: 94Effects of Li Substitution in Bi-2223 Superconductors(Springer Verlag, 2008) Bilgili, Özlem; Selamet, Yusuf; Kocabaş, KemalThe effects of Li substitution on the properties of high temperature superconductor Bi 17Pb 0.3Sr 2C 2Cu 3-x Li x O y were investigated. The samples were prepared by substituting Li (x=0.00-0.20) with changing ratios by a solid state reaction method. The samples were characterized by X-ray diffraction, DC electrical resistivity, AC magnetic susceptibility, and scanning electronic microscopy (SEM). The X-ray diffraction studies were done at room temperature and the lattice constants of the material were determined by indexing all the peaks observed. This study shows that there are two coexisting phases; high-T c (2223) phase and low-T c (2212) phase. The lattice structure of the material belongs to the orthorhombic unit cell. The volume fraction was estimated from the intensities of Bi-(2223) and Bi-(2212) phases. The sample with 20 wt% of added Li showed the higher volume fraction of Bi-(2223) phase formed (81%) compared to the other samples. The DC electrical resistivity of all the samples decreased as the wt% of Li increased. Both the onset critical temperatures T c (onset) and zero electrical resistivity critical temperatures T c (R=0) of the samples were determined from the DC electrical resistivity measurements. The observed value of the onset critical T c (onset) temperature was 110 K agreeing well with the magnetic susceptibility measurements. We obtained T c onset at 112 K from AC magnetic susceptibility measurements. © 2008 Springer Science+Business Media, LLC.