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    A comparative photoluminescence study on Mn-Free GaAs/AlAs and Mn-containing Ga1-xMnxAs/AlAs quantum wells (QWs) grown on various orientations by MBE
    (Taylor & Francis Ltd, 2016) Gunes, M.; Erken, O.; Gumus, C.; Yalaz, E.; Pesen, E.; Ukelge, M. O.; Arpapay, B.
    Optical properties of diluted magnetic semiconductor Ga0.999Mn0.001As/AlAs quantum well structures grown on (1 0 0 ), (1 1 0), (3 1 1)B and (4 1 1)B by molecular beam epitaxy are reported. Temperature-dependent spectral photoluminescence (PL) measurement was performed at temperatures between 15 and 300K. The PL measurements showed that band gap of the alloy decreases with increasing lattice temperature regardless the growth orientations. S-shaped temperature dependence has been observed in the samples grown on (1 0 0), (3 1 1)B, (4 1 1)B orientations. PL emission energy is fitted with Varshni and Bose-Einstein Approximation to determine Debye temperature (beta), (Theta(E)) and thermal expansion coefficient (alpha), the exciton-phonon coupling strength (a(B)).
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    A study of the electronic and physical properties of SnO2 thin films as a function of substrate temperature
    (Elsevier Sci Ltd, 2019) Erken, O.; Ozkendir, O. M.; Gunes, M.; Harputlu, E.; Ulutas, C.; Gumus, C.
    In this work, tin dioxide (SnO2) thin films were prepared at various substrate temperatures (380-440 degrees C, in steps of 20 degrees C) on glass substrates by the Spray Pyrolysis Method. X-ray Diffraction (XRD) measurements revealed that the SnO2 thin films were formed in a tetragonal crystallized structure. The electronic structure of the tin dioxide thin films that were prepared at several substrate temperatures were investigated with the collected X-ray Absorption Spectroscopy (XAS) data. The crystal structure analysis was also supported by the Extended X-ray Absorption Fine Structure (EXAFS) data analysis extracted from the X-ray Absorption Fine Structure (XAFS) data. Unstable crystal behaviors were detected in the samples due to metastable SnO structure formations as a result of phase transitions from the SnO to SnO2 structure during the annealing processes. Clear information on the atomic displacements in the samples as a picture of the crystal mechanism was obtained from the analysis of EXAFS data. The SnO2 thin films were found to exhibit high transmittance (average 90%) in the 400-1100 nm interval. The thickness of the SnO2 thin film (t) and refractive index (n) were calculated from transmittance spectra in the visible region using envelope method. The direct energy band gaps of the films obtained were 4.01-4.09 eV. Atomic force microscope (AFM) measurements were performed in order to investigate the surface roughness of the SnO2 thin films.
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    Effect of doping on transport properties of InSb epilayers grown by MOCVD and MBE
    (Elsevier, 2024) Gunes, M.; Aydin, M.; Donmez, O.; Gumus, C.; Erol, A.; Marroquin, J. F. R.; Felix, J. F.
    Temperature-dependent carrier transport properties of two InSb epilayers grown on GaAs substrates by Molecular Beam Epitaxy (MBE) and Metal Organic Chemical Vapor Deposition (MOCVD) are investigated. The InSb epilayer grown by MBE was undoped, but the undoped InSb epilayer grown by MOCVD was grown on a thin Zndoped InSb layer. Hall Effect results showed that the Hall coefficients (RH) for InSb grown by MBE and MOCVD are negative in temperature ranges 4.2 K-300 K and 200 K-300 K, respectively. However, for the InSb sample grown by MOCVD, RH switches from a positive to a negative value for temperatures above similar to 180 K, which could be due to the capture electrons generated from dislocation between InSb and GaAs by Zn atoms. The electron mobilities of InSb grown by MBE and MOCVD were 38,247 and 51,704 cm(2)/Vs, respectively. Low-temperature magnetoresistance measurements showed clear Shubnikov-de-Haas oscillations (SdH) in MBE InSb; however, no SdH oscillations were observed in MOCVD InSb samples.
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    Effect of molar concentration on the structural, linear and nonlinear optical properties of CuS (covellite) thin films
    (Elsevier Ltd, 2022) Habiboglu, C.; Erken, O.; Gunes, M.; Yilmaz, O.; Cevlik, H.C.; Ulutas, C.; Gumus, C.
    CuS thin films with various molar concentrations at 70 °C temperature were deposited by Chemical Bath Deposition. The effect of molar concentration on the structural, linear optic, nonlinear optic and morphological properties of CuS films were deeply investigated. X-ray diffraction (XRD) analysis exhibited that CuS films were formed in polycrystal structure and hexagonal phase. The fundamental optical parameters of films such as energy band gap, reflection and extinction coefficient were determined with the results of optical transmission and optical absorption by UV–vis spectrophotometer. The energy band gap values were reduced with increasing films thickness. Moreover, the dependence of the optical dielectric constants, loss tangent, optical conductivity, surface and volume energy loss function values on the molar concentrations were studied. Furthermore, the third order nonlinear optical susceptibility and nonlinear refractive index, which is considered to be the base of the first order optical susceptibility with nonlinear optical properties were discussed in detail. © 2022 Elsevier Ltd
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    Effect of the deposition time on optical and electrical properties of semiconductor ZnS thin films prepared by chemical bath deposition
    (Natl Inst Science Communication-Niscair, 2017) Erken, O.; Gunes, M.; Ozaslan, D.; Gumus, C.
    Semiconductor ZnS thin films have been deposited by a chemical bath deposition (CBD) on a glass substrate at 80 degrees C with different deposition time (4, 6 and 8 h), The films have been further studied in order to determine the change in optical and electrical properties as a function of deposition time. The film thicknesses have been calculated between 210 - 1375 nm by using gravimetrical analysis. The optical properties of ZnS thin films have been determined by transmittance (%T) and absorbance (A) measurements by UV-Vis spectroscopy operated wavelength range between 300 and 1100 nm at room temperature. The optical transmittance values of ZnS thin films in the visible region of the electromagnetic spectrum have been found to be between 51-90%. The calculations indicate that the refractive index (n) in the visible region is between 1.40 and 2.45. The optical band gaps (E-g) of thin films have been calculated between 3.61-3.88 eV while the band edge sharpness values (B) are varied between 6.95 x 10(9)-8.96 x 10(10) eV/cm(2). The specific resistivity values (p) of the films are found to be between 1.08 x 10(5)-1.01 x 10(6) Omega.cm and exhibit an n-type conductivity by Hall measurement.
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    Effect of the deposition time on optical and electrical properties of semiconductor ZnS thin films prepared by chemical bath deposition
    (National Institute of Science Communication and Information Resources (NISCAIR), 2017) Erken, O.; Gunes, M.; Ozaslan, D.; Gumus, C.
    Semiconductor ZnS thin films have been deposited by a chemical bath deposition (CBD) on a glass substrate at 80 °C with different deposition time (4, 6 and 8 h). The films have been further studied in order to determine the change in optical and electrical properties as a function of deposition time. The film thicknesses have been calculated between 210 - 1375 nm by using gravimetrical analysis. The optical properties of ZnS thin films have been determined by transmittance (%T) and absorbance (A) measurements by UV-Vis spectroscopy operated wavelength range between 300 and 1100 nm at room temperature. The optical transmittance values of ZnS thin films in the visible region of the electromagnetic spectrum have been found to be between 51-90%. The calculations indicate that the refractive index (n) in the visible region is between 1.40 and 2.45. The optical band gaps (Eg) of thin films have been calculated between 3.61-3.88 eV while the band edge sharpness values (B) are varied between 6.95 × 109-8.96 × 1010 eV/cm2. The specific resistivity values (p) of the films are found to be between 1.08 × 105-1.01 × 106 ?cm and exhibit an n-Type conductivity by Hall measurement.
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    Influence of post-deposition annealing on the structural and optical properties of ?-MnS thin film
    (Elsevier Gmbh, 2018) Ulutas, C.; Gunes, M.; Gumus, C.
    gamma-MnS thin film was deposited at 40 degrees C temperature on glass substrate by Chemical Bath Deposition (CBD) method that has superior advantageous in terms of fast and cheap production. MnS thin film was annealed in nitrogen atmosphere at temperatures 100, 200, 300, 400, 500 C for an hour. The effect of annealing temperature on structural and optical properties have been investigated. X-ray diffraction (XRD) analysis revealed that gamma-MnS thin film had the phase change and oxidized at 400,500 C annealing temperature. The grain size of the annealed film was calculated between 241 and 280 angstrom as a function of annealing temperature. It was observed that optical transmission values decreased at wavelength of 400-700 nm (visible region) after annealing at temperatures 400 and 500 degrees C. Increasing annealing temperature induces reduction in energy band gap values from 3.89 eV down to 3.46 eV. Refractive index (n) values were calculated by envelope method: Refractive index values at visible region increased from 2.03 to 2.54 with increasing annealing temperature. (C) 2018 Elsevier GmbH. All rights reserved.
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    Investigation of properties the copper sulfide thin films prepared from different copper salts
    (Elsevier Gmbh, Urban & Fischer Verlag, 2018) Erken, O.; Gunes, M.; Kirmizigul, F.; Gumus, C.
    Copper sulfide (CuS) thin films were prepared on commercial glass substrates by Chemical Bath Deposition (CBD) method using solution of different copper salts at 50 degrees C temperature for seven hours. Different anions of copper salts that is crucial for the properties of the films affect the precipitation mechanism and growth rate. For this reason, the effect of the different copper salts on the properties of CuS thin films was investigated and discussed. The influence of the different copper salts in the chemical bath was determined by means of optical transmission of the thin films in the wavelength range of 400-1100 nm taken at room temperature. Next, using these data, the optical band gap values E-g, the extinction coefficient k, the refractive index n, and the real epsilon(1) and imaginary parts epsilon(2) of the dielectric constant were calculated. The crystallographic structure of CuS thin films were analyzed with an X-ray diffractometer (XRD). XRD analysis was revealed the polycrystalline and hexagonal phase of CuS thin films. The surface roughness of the films were measured by AFM. The surface roughness of the thin films was different despite the same deposition time.
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    Investigation on the electronic and physical properties of gamma-MnS films as a function of thickness
    (Elsevier Sci Ltd, 2022) Ulutas, C.; Erken, O.; Gunes, M.; Ozkendir, O. M.; Gumus, C.
    In this study, gamma-manganese sulphide (gamma-MnS) films were prepared at various thickness and deposition time at a temperature of 50 degrees C by Chemical Bath Deposition Method (CBD). The characterization of the gamma-MnS films were determined by using the following methods; X-ray Absorption Fine Structure Spectroscopy (XAFS), Xray diffraction (XRD), optical absorption, Field Emission-Scanning Electron Microscope (FE-SEM), Energy Dispersive X-ray analysis (EDX). The electronic interplay via the coupling between Mn 3d levels and S 2p levels was determined to build up strong molecular bonds containing broad band with hybrid pd levels at low energy levels. The results of the electronic structure analysis were also tested with the absorption spectroscopy calculations and high agreement is reported. XRD analysis revealed that the film deposited for 5 h had amorphous structure and turned to be crystal structure in hexagonal phase with deposition time 10, 15, 20 h due to increasing film thickness value. The optical band gap values were reduced from 3.86 eV to 3.10 eV with increasing film thickness. The average refractive index value of films at visible region were calculated between 1.55 and 2.81 as a function of increment in film thickness. The mobility and resistivity of the films were measured as 8.65-55.76 cm2/Vs and 3.10 x 105-2.39 x 106 omega cm, respectively, by Hall measurement.
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    Optical properties of GaAs1-xBix/GaAs quantum well structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates
    (Iop Publishing Ltd, 2018) Gunes, M.; Ukelge, M. O.; Donmez, O.; Erol, A.; Gumus, C.; Alghamdi, H.; Galeti, H. V. A.
    In this work, the electronic bandstructure of GaAs1-xBix/GaAs single quantum well (QW) samples grown by molecular beam epitaxy is investigated by photomodulated reflectance (PR) measurements as a function of Bi content (0.0065 <= x <= 0.0215) and substrate orientation. The Bi composition is determined via simulation of high-resolution x-ray diffraction measurement and is found to be maximized in the 2.15%Bi and 2.1%Bi samples grown on (100) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi QW layer but extends out of the GaAsBi QW towards the GaAs barrier and forms a GaAsBi epilayer. PR spectra are fitted with the third derivative function form (TDFF) to identify the optical transition energies. We analyze the TDFF results by considering strain-induced modification on the conduction band (CB) and splitting of the valence band (VB) due to its interaction with the localized Bi level and VB interaction. The PR measurements confirm the existence of a GaAsBi epilayer via observed optical transitions that belong to GaAsBi layers with various Bi compositions. It is found that both Bi composition and substrate orientation have strong effects on the PR signal. Comparison between TDFF and calculated optical transition energies provides a bandgap reduction of 92 meV/%Bi and 36 meV/%Bi and an interaction strength of the isolated Bi atoms with host GaAs valence band (C-BiM) of 1.7 eV and 0.9 eV for (100) and (311)B GaAs substrates, respectively.
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    Study of the electronic properties of Cu2O thin films by X-ray absorption spectroscopy
    (Elsevier Gmbh, 2018) Ozaslan, D.; Ozkendir, O. M.; Gunes, M.; Ufuktepe, Y.; Gumus, C.
    We have investigated the thickness effect of Cu2O thin films on the electronic structure deposited by the successive ionic layer adsorption and reaction (SILAR) method. Crystal, optical and electronic properties of the Cu2O thin films were studied by X-ray diffraction (XRD) and X-ray absorption near edge spectroscopy (XANES). According to the crystal structure analysis, films were determined to be mainly in cubic Cu2O structures. The XANES study have shown that Cu L-2,L-3 absorption edges are influenced by the chemical state of the Cu atoms strongly and a sole ionic picture is not enough to describe the L-edge spectra of Cu2O. It has been observed that Cu L-2,L-3-edge spectra of the samples present typical electronic features of both monovalent Cu (I) and Cu (II) divalent states. The grains have an average size of 2.5 nm and XRD measurements revealed that (111) plane is the preferential orientation. Optical studies have shown that the optical absorption edge shifted to higher energies as the film thickness increases. It was found that the optical band gap was significantly influenced by the film thickness. Our results exhibited that the increment of the optical band gap of Cu2O thin films associated with a significant decrease of Cu-Cu interaction as a result of the increase in the film thickness. (C) 2017 Elsevier GmbH. All rights reserved.
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    The effect of annealing temperature on the physical properties of Cu2O thin film deposited by SILAR method
    (Elsevier, 2020) Ozaslan, D.; Erken, O.; Gunes, M.; Gumus, C.
    Cu2O film was deposited on a glass substrate at 70 degrees C by the SILAR (Successive Ionic Layer Adsorption and Reaction) method. The Cu2O film was annealed in an air atmosphere at 100 degrees C, 300 degrees C, and 500 degrees C temperatures for 1 h and the effect of the annealing temperature on the physical properties was investigated. The phase-transition temperature that corresponds to the transformation from Cu2O to CuO was occurred at temperature of approximately 300 degrees C with annealing process. The energy band gap (E-g) was reduced from 2.57 eV to 1.91 eV with the increasing annealing temperature. Hall measurement revealed that the film showed p-type conductivity and the resistivity (rho) of Cu2O deposited at 70 degrees C and annealed 100 degrees C were calculated as 6.12 x 10(4) and 7.44 x 10(3 )Omega cm, respectively, while the film annealed at 300 degrees C and 500 degrees C the resistivity of CuO was found to be 8.23 x 10(3) and 5.11 x 10(2) Omega em, respectively.
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    The effect of strain and spatial Bi distribution on the band alignment of GaAsBi single quantum well structure
    (Elsevier, 2021) Gunes, M.; Donmez, O.; Gumus, C.; Erol, A.; Alghamdi, H.; Alhassan, S.; Alhassni, A.
    The band line-up and band offset calculations of GaAs0.978Bi0.022/GaAs single quantum well with spatial changes of Bi composition were reported. The spatial Bi profile and a certain amount of the Bi composition in the barrier layer were determined by HR-XRD measurements. Virtual Crystal Approximation and Valence Band Anti-Crossing models were used including strain effects to obtain conduction and valence band edge shifts with Bi incorporation. Photoluminescence (PL) measurements were performed at a low temperature of 8 K as a function of excitation intensity. The PL spectra have shown asymmetric line shapes, which were fitted with different Gaussian functions. Comparing experimental PL results with calculated band edge energies, it was found that optical transition is a type I under low intensity excitation while the optical transition is switched from type I to type II due to the spatial changes in Bi concentrations. The band offsets Delta E-c/Delta E-v were also determined.
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    The effects of substrate on the physical properties of gamma-MnS thin films deposited by chemical bath deposition
    (Elsevier B.V., 2020) Ulutas, C.; Erken, O.; Gunes, M.; Gumus, C.
    Gamma-MnS thin films were deposited on glass and indium tin oxide (ITO) substrates at 40 °C temperature by Chemical Bath Deposition (CBD) method. XRD measurements revealed that the gamma-MnS films are polycrystalline in the wurtzite phases and show a preferential orientation along the c-axis. The grain size of the films that were deposited onto the glass and ITO were calculated as 327 nm and 189 nm, respectively. The energy band gap of the films deposited onto glass and ITO were also calculated as 3.56 eV, 3.74 eV, respectively. The refractive index of the gamma-MnS at the visible region (400–700 nm) were measured as 2.1 and 1.63 for the glass and ITO substrates, respectively. Hall measurement revealed that the gamma-MnS films showed n-type conductivity and the resistivity of the gamma-MnS films deposited on the glass and ITO substrates were measured as 7.1 × 105 ?cm, 3.04 × 102 ?cm, respectively. © 2020 Elsevier B.V.
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    The influence of trisodium citrate dihydrate complexing agent on the structural, electrical and optical properties of ?-MnS thin films
    (Springer, 2023) Budak, Z.; Ulutas, C.; Yilmaz, O.; Cevlik, H. C.; Gunes, M.; Gumus, C.
    gamma-MnS films were prepared using trisodium citrate (TSC) complexing agents at different molarity values (0.5, 1 and 1.5 M). Characterization techniques such as X-ray Diffraction (XRD), optical absorption spectra, Field Emission-Scanning Electron Microscope (FE-SEM), Energy Dispersive X-ray (EDX) and Hall Effect were used to determine the properties of the films. As a result of XRD analysis, it was observed that the films prepared with 0.5 M TSC were formed in amorphous structure, while the films prepared with 1 M and 1.5 M TSC were formed in polycrystalline structure and hexagonal phase. In addition, it was determined that the crystallization of the films increased with the increase in the molarity of TSC. The optical gaps of the films were determined as 3.77 eV, 3.44 eV and 3.40 eV, respectively, depending on the increase in molarity of TSC. The refractive index values of the MnS films in the visible region (400-700 nm) were calculated as 1.87, 2.02 and 2.10, respectively. Electrical resistivity and mobility values from Hall Effect measurements were measured as 1.01 x 10(6), 9.68 x 10(5), 4.10 x 10(5) ohm cm and 33.01, 36.93, 56.53 cm(2)/Vs, respectively, depending on the increase in TSC molarity value.