Browsing by Subject "Semiconducting selenium compounds"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Open Access Band Structure and Optical Properties of Kesterite Type Compounds: First principle calculations(Institute of Physics Publishing, 2017) Palaz S.; Unver H.; Ugur G.; Mamedov, Amirullah; Özbay, EkmelIn present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated. © Published under licence by IOP Publishing Ltd.Item Open Access Electrical properties from photoinduced charging on Cd-doped (100) surfaces of CuInSe2 epitaxial thin films(AVS Science and Technology Society, 2016) Johnson, N.; Aydogan, P.; Süzer, Şefik; Rockett, A.The photoresponse of Cd-doped CuInSe2 (CIS) epitaxial thin films on GaAs(100) was studied using x-ray photoelectron spectroscopy under illumination from a 532 nm laser between sample temperatures of 28-260 °C. The initial, air-exposed surface shows little to no photoresponse in the photoelectron binding energies, the Auger electron kinetic energies or peak shapes. Heating between 50 and 130 °C in the analysis chamber results in enhanced n-type doping at the surface and an increased light-induced binding energy shift, the magnitude of which persists when the samples are cooled to room temperature from 130 °C but which disappears when cooling from 260 °C. Extra negative charge trapped on the Cu and Se atoms indicates deep trap states that dissociate after cooling from 260 °C. Analysis of the Cd modified Auger parameter under illumination gives experimental verification of electron charging on Cd atoms thought to be shallow donors in CIS. The electron charging under illumination disappears at 130 °C but occurs again when the sample is cooled to room temperature.Item Open Access First principles prediction of the elastic, electronic, and optical properties of Sb 2S 3 and Sb 2Se 3 compounds(2012) Koc H.; Mamedov, A.M.; Deligoz, E.; Ozisik H.We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb 2S 3 and Sb 2Se 3 compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. © 2012 Elsevier Masson SAS. All rights reserved.Item Open Access Interaction of adatoms and molecules with single-layer arsenene phases(American Chemical Society, 2016-06) Ersan, F.; Aktürk, E.; Çıracı, SalimRecent studies have shown that arsenic can form single-layer phases in buckled honeycomb as well as symmetric washboard structures, named as arsenene. These structures are stable even in freestanding form and are nonmagnetic semiconductors in the energy range which is suitable for various electronic applications. In this study we investigated the adsorption of selected adatoms (H, Li, B, C, N, O, Al, Si, P, Cl, Ti, Ga, Ge, As, Se, and Sb) and physisorption of molecules (H2, O2, and H2O) to these two arsene phases. Since the interaction of these adspecies with arsenene are studied using large supercells, the coupling between adspecies is minimized, and hence our results can be interpreted to mimic the effects of isolated adatom or physisorbed molecule. It is found that the adatoms form strong chemisorption bonds and hence modify the atomic structure and physical properties locally. Some of the adatoms give rise to significant local reconstruction of the atomic structure. Electronic states of some adatoms become spin polarized and attain net magnetic moments; they may even display half-metallic character at high coverage. A majority of adsorbed atoms give rise to localized states in the fundamental band gap. We showed that the interactions between H2, O2, and H2O molecules and single-layer arsenene are rather weak and do not cause any significant changes in the physical properties of these molecules, as well as those of arsenene phases. However, some of these molecules can be dissociated at the edges of the flakes of arsenene structures; their constituents are adsorbed to the edge atoms and cause local reconstructions.Item Open Access Peculiar piezoelectric properties of soft two-dimensional materials(American Chemical Society, 2016-06) Sevik, C.; Çakır, D.; Gülseren, O.; Peeters, F. M.Group II-VI semiconductor honeycomb monolayers have a noncentrosymmetric crystal structure and therefore are expected to be important for nano piezoelectric device applications. This motivated us to perform first-principles calculations based on density functional theory to unveil the piezoelectric properties (i.e., piezoelectric stress (e11) and piezoelectric strain (d11) coefficients) of these monolayer materials with chemical formula MX (where M = Be, Mg, Ca, Sr, Ba, Zr, Cd and X = S, Se, Te). We found that these two-dimensional materials have peculiar piezoelectric properties with d11 coefficients 1 order of magnitude larger than those of commercially utilized bulk materials. A clear trend in their piezoelectric properties emerges, which originates mainly from their mechanical properties. We establish a simple correlation between the piezoelectric strain coefficients and the physical properties, as the natural elemental polarizabilities, the Bader charges, and lattice constants of the individual M/X atoms and MX monolayers.Item Open Access Synthesis of stable mesostructured coupled semiconductor thin films: meso-CdS-TiO2 and meso-CdSe-TiO2(2010) Okur, H. İ.; Türker, Y.; Dag, Ö.Cd(II) ions can be incorporated into the channels of mesostructured titania films, using the evaporation-induced self-assembly (EISA) approach, up to a record high Cd/Ti mole ratio of 25%. The film samples were obtained by spin or dip coating from a mixture of 1-butanol, [Cd(H20)4] (N03)2, HNO3, and Ti(OC4H 9)4 and then aging the samples under 50% humidity at 30 0C (denoted as meso-xCd(II)-y TiO2). The nitrate ions, from nitric acid and cadmium nitrate, play important roles in the assembly process by coordinating as bidentate and bridged ligands to Cd(II) and Ti(IV) sites, respectively, in the mesostructured titania films. The film samples can be reacted under a H 2S (or H2Se) gas atmosphere to produce CdS (or CdSe) on the channel surface and/or pore walls. However, the presence of such a large number of nitrate ions in the film samples also yields an extensive amount of nitric acid upon H2S (or H2Se) reaction, where the nanoparticles are not stable (they undergo decomposition back to metal ion and H2S or H2Se gas). However, this problem can be overcome by further aging the samples at 130 °C for a few hours before H2S (or H2Se) reaction. This step removes about 90% of the nitrate ions, eliminates the nitric acid production step, and stabilizes the CdS nanoparticles on the surface and/or walls of the pores of the coupled semiconductor films, denoted as meso-xCdS-yTiO2. However, the H2Se reaction, additionally, needs to be carried at lower H2Se pressures in an N2 atmosphere to produce stable CdSe nanoparticles on the surface and/or walls of the pores of the films, denoted as meso-xCdSe-.yTiO2. Otherwise, an excessive number of Se8 particles form in the film samples.