Browsing by Author "Akcay, N."

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Characteristics of CZTSSe Thin Films Prepared by Selenization of Sputtered Cu, Sn and ZnS Layers
(2019) Akcay, N.; Ozcelik, S.; Zaretskaya, E.; Juskenas, R.; 0000-0002-3948-5629; ABB-7017-2020
We reported the growth of CZTSSe thin films on Mo-coated SLG substrates by the two-step approach which includes the deposition of precursor films by the magnetron sputtering method at room temperature followed by selenization of the precursor films at 560 degrees C. Formation of CZTSSe films with the kesterite structure was confirmed by XRD and Raman spectroscopy analyses. The films are slightly Cu-rich and Zn-deficient. SEM study shown that the films have uniform surface morphology and densely packed structure without any voids and cracks.
Characterization of Cu2ZnSnS4 thin films prepared with and without thin Al2O3 barrier layer
(2022) Akcay, N.; Gremenok, V; Ivanov, V. A.; Zaretskaya, E.; Ozcelik, S.; 0000-0002-3948-5629
We investigated the effect of thin Al2O3 barrier layer (similar to 20 nm) deposited by radio frequency magnetron sputtering technique on the structural, morphological, optical, and electrical properties of Cu2ZnSnS4 (CZTS) films. Major differences in the crystalline qualities of the films were not observed with the addition of the Al2O3 layer except for a small decrease in crystallite size. Raman spectra of the film with the Al(2)O(3 )layer exhibited the peaks belonging to ZnS and Cu2-xS secondary phases. X-ray photoelectron spectroscopy analysis showed that SO42- and CuSO4 compounds were formed on the surfaces of the films. The formation of the CuSO4 phase was associated with the bonding between CuO and S in an oxidized CZTS surface. The presence of the ZnS, Cu2-xS secondary phases, and CuSO4 on the surfaces of the films were also confirmed by scanning electron microscopy images. The film with the Al2O3 layer differed from the other films with its surface that have randomly distributed porous- structured agglomerations and a decrease in the ZnS secondary phases on its surface. All films exhibited different Na distributions in secondary ion mass spectroscopy depth profiles. The Al2O3 layer caused a slower gradient in Na diffusion with decreasing the accumulation of Na element at a distinct region. The activation energy for the thermally activated band conduction was calculated as 0.030 eV and attributed to the thermal release of the holes from the vacancy of copper (V-Cu) defect states. The results of temperature-dependent conductivity measurements indicated that there were different conduction mechanisms in the films.
Fabrication and Properties of Molybdenum Disulfide Films for Electro-Optical Applications
(2019) Ozcelik, S.; Akcay, N.; Tivanov, M.; 0000-0002-3948-5629; ABB-7017-2020
MoS2 films on sapphire and SiO2/Si substrates were fabricated by sulfurization of sputtered Mo precursor films at 900 degrees C in a two-zone furnace. Structural, morphological, optical and electrical properties of the films were determined. The films of MoS2 were successfully grown on the substrates with polycrystalline structures and proposed to be used in electro-optical devices.
Influence of Sulfurization Time on the Properties of Cu2ZnSnS4 Thin Films Deposited on Mo-coated Soda Lime Glass Substrates by Co-sputtering Technique
(2020) Akcay, N.; Ataser, T.; Ozen, Y.; Ozcelik, S.; 0000-0002-3948-5629; ABB-7017-2020
In this work, Cu2ZnSnS4 (CZTS) absorber films were prepared by sulfurization of co-sputtered precursor films at different time periods. The influence of sulfurization time on physical characteristics of the grown films was investigated in detail. The sulfurized CZTS films exhibited the characteristic diffraction peak of the kesterite phase corresponding to the (112) crystal plane, the main Raman mode of kesterite phase at around 337 cm(-1) and Cu-deficient and Zn-rich composition. From the atomic force microscopy surface and cross-sectional scanning electron microscopy images, it was revealed out that the films were uniform, compact without any cracks and consisted of micron-sized and closely packed grains. In addition, the films showed tail-to-tail, band-to-tail and band-to-band transitions at around 1.41 eV (E-1), 1.45 eV (E-2) and 1.51 eV (E-3), respectively. Secondary ion mass spectroscopy analysis showed that the sodium ions deeply diffused through the molybdenum layer into the CZTS film from the soda lime glass substrate for all samples. All of the films exhibited an optical band gap of around 1.4 eV, an absorption coefficient over 10(4) cm(-1), p-type conductivity with a high concentration of free holes in the order of 10(17)-10(18) cm(-3) and low mobility in the range from 0.63 cm(2)/V.s to 8.11 cm(2)/V.s.
MoS2 Thin Films Grown by Sulfurization of DC Sputtered Mo Thin Films on Si/SiO2 and C-Plane Sapphire Substrates
(2021) Akcay, N.; Tivanov, M.; Ozcelik, S.; https://orcid.org/0000-0002-3948-5629; ABB-7017-2020
Here we report the growth of molybdenum disulfide (MoS2) films with different thicknesses on silicon dioxide/silicon (SiO2/Si) and c-plane sapphire substrates by sulfurization of direct current (DC) sputtered Mo precursor films in a chemical vapor deposition furnace with sulfur powder at 900 degrees C. The structural, morphological, optical, and electrical properties of the films on different substrates were investigated through a series of characterization in detail. X-ray diffraction (XRD) results showed that the grown films on sapphire substrates had better crystallization and a well-stacked layered structure than the films on SiO2/Si substrates. The frequency difference between the characteristic modes E-2g(1) and A(1g) of hexagonal phase MoS2 was determined as similar to 26 cm(-1) which is consistent with the typical value of bulk MoS2. Energy-dispersive x-ray (EDX) spectra exhibited that the films were near-stoichiometric. A small shift towards the lower binding energies in the Mo 3d(5/2) peak positions was observed due to the valency of Mo below +4 depending on the compositional ratios of the films in x-ray photoelectron spectroscopy (XPS) spectra. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis indicated that the films had smooth surfaces and a well-packed crystal structure. However, when the thickness of the films deposited on sapphire substrates increased, the strain between the sapphire substrate and MoS2 film caused the formation of the micro-domes in the film. In addition, the films exhibited high absorption and reflection properties in the near-infrared (NIR) and mid-infrared (MIR) regions in Fourier transform infrared (FTIR) analysis. Therefore, it is considered that the films can be used for photodetector applications in these regions and infrared shielding coating applications.
Na Incorporation into Cu2ZnSnS4 Thin Film Absorbers from RF-Sputtered Naf Precursors
(2021) Akcay, N.; Baskose, U. Ceren; Ozcelik, S.; Gremenok, V. F.; Zaretskaya, E. P.; AAZ-3546-2020
In this work, we report the incorporation of sodium (Na) alkaline element into copper-zinc-tin-sulphide (Cu-Zn-Sn-S) precursor films by adding radio frequency (RF)-sputtered sodium fluoride (NaF) intermediate layers bringing a new approach to the bifacial sodium-incorporated treatment (BIST) and its effect on the properties of Cu2ZnSnS4 (CZTS) absorber films. Due to the absence of alkaline diffusion barrier layers on soda lime glass (SLG) substrates, Na additions from both NaF intermediate layers and SLG substrate were evaluated together. With additional NaF intermediate layers among the elemental metal stacks, the films exhibited better crystalline properties and a more compact structure. However, the amount of the Cu2-xS secondary phases formed on the surfaces increased by the additional NaF layers. Raman spectra confirmed the formation of the kesterite phase and showed the peaks corresponding to Cu3SnS4 and Cu2-xS secondary phases. Na diffusion originating from NaF layers deposited on molybdenum (Mo) films occurred in both directions of the CZTS film and the SLG substrate. The photoluminescence (PL) bands located at around 1.40 eV were attributed to the band to band (BB) transitions. The film with additional NaF intermediate layers exhibited higher carrier concentrations and lower resistivity than the other film due to the presence of the higher amount of Cu2-xS secondary phases on its surface.