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Analysis of mixed optical transitions in dilute magnetic AlAs/GaAs/ GaMnAs quantum wells grown on high substrate index by molecular beam epitaxy
(Elsevier, 2023) Kerimova, Shemshat; Donmez, Omer; Gunes, Mustafa; Kuruoglu, Furkan; Aydin, Mustafa; Gumus, Cebrail; Erol, Ayse
In this study, we report the influence of high-index substrate orientation on the optical properties of dilute Mn containing a single quantum well (QW) structure grown by molecular beam epitaxy (MBE). The electronic band structure of the samples is calculated with finite element methods (FEM). Photomodulated reflectance (PR) spectroscopy is employed to determine the optical transition energies at room temperature. PR experimental results are analyzed with the Third Derivative Functional Form (TDFF) signal function. TDFF fitting shows that the optical transition starts below the fundamental GaAs bandgap energy for the samples grown on (311) B and (411) B-oriented substrates. Comparing TDFF fitting and calculated optical transition energies with FEM show that the optical transition occurs in type-I and type-II as direct and indirect transitions, respectively. Type-I and -II optical transitions are addressed concerning the electronic band structure of the sample grown on oriented substrates.
Determination of electronic band structure of quaternary ferromagnetic Ga0.97-yMn0.03CryAs epitaxial layers
(Elsevier, 2023) Donmez, Omer; Gunes, Mustafa; Henini, Mohamed; Erol, Ayse
Introducing transition metals to conventional III-V semiconductors anomalously changes their fundamental characteristics, such as electronic, magnetic, and structural properties. In this study, we show that the valence band anti-crossing (VBAC) model can be exploited to calculate the electronic band structure of the quaternary Ga0.97-xMn0.03CrxAs epitaxial layers. In this model, the localized Mn and Cr defect states interact with the valence band states (VB), reconstructing VBs and splitting each VB state. The splitting top of the VB state forms an impurity band (IB) and fundamental VB edge. Photomodulated reflectance (PR) spectroscopy is exploited to determine optical transition energies at room temperature. PR spectra were analyzed with the third derivative functional form (TDFF) signal's line shape. The experimental optical transition energies, including band-to-band and spin split-off band transitions, match the calculated optical transition energies by the VBAC model. In the calculation, the interaction energy between localized Mn/Cr-energy level and valence band edges is experi-mentally determined as 0.7 eV.
Direct impregnation and characterization of Colemanite/Ulexite-Mg(OH)2 paraffin based form-stable phase change composites
(Elsevier, 2019) Horpan, M. Safa; Sahan, Nurten; Paksoy, Halime; Sivrikaya, Osman; Gunes, Mustafa
Paraffin is mainly preferred as an organic phase change material (PCM) in thermal energy storage (TES) systems especially for cooling and heating of buildings implementations. In order to develop form-stable and thermally stable blends natural minerals (Colemanite, Ulexite and Mg(OH)(2)) were used to prepare composites via direct impregnation method. These mineral compounds are abundant locally and known to be thermally stable as they show multi-step thermal decompositions. Thermal, morphological and chemical properties of these composites were characterized by thermogravimetric analysis (TGA), the differential scanning calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM). Results of analyses indicate that the introduction of mineral phase to the paraffin is achieved adequately despite of minor mixing problems that show a form-stable behaviour. Comparing energy storage abilities of these composites, Mg(OH)(2) or Colemanite containing blends are found to be the promising composites.
Effect of Annealing Temperature on The physical Properties of Mn3O4 Thin Film Prepared by Chemical Bath Deposition
(Esg, 2016) Ulutas, Cemal; Erken, Ozge; Gunes, Mustafa; Gumus, Cebrail
In this study, Mn3O4 thin film was prepared by the chemical bath deposition (CBD) method on commercial microscope glass substrate deposited at 30 degrees C. The Mn3O4 film was annealed in an air atmosphere for an hour at temperatures 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C, respectively. The effect of annealing temperature on structural and optical properties such as optical constants of extinction coefficient (k), refractive index (n), the real (epsilon(1)) and imaginary (epsilon(2)) part of the dielectric constant and energy band gap (E-g) of the film were determined. The experimental characterization techniques included X-ray diffraction (XRD), UV-vis spectrophotometer and Hall effect measurement. XRD analysis showed that the film is grown in a polycrystalline structure in tetragonal phase. The conductivity of the film as a function of annealing temperature was measured as (1.32-6.65)x10(-6) (Omega cm)(-1).
Effect of annealing temperature on the physical properties of Mn3O4 thin film prepared by chemical bath deposition
(Electrochemical Science Group, 2016) Ulutas, Cemal; Erken, Ozge; Gunes, Mustafa; Gumus, Cebrail
In this study, Mn3O4 thin film was prepared by the chemical bath deposition (CBD) method on commercial microscope glass substrate deposited at 30° C. The Mn3O4 film was annealed in an air atmosphere for an hour at temperatures 100° C, 200° C, 300° C, 400° C, 500° C, respectively. The effect of annealing temperature on structural and optical properties such as optical constants of extinction coefficient (k), refractive index (n), the real (?1) and imaginary (?2) part of the dielectric constant and energy band gap (Eg) of the film were determined. The experimental characterization techniques included X-ray diffraction (XRD), UV-vis spectrophotometer and Hall effect measurement. XRD analysis showed that the film is grown in a polycrystalline structure in tetragonal phase. The conductivity of the film as a function of annealing temperature was measured as (1.32-6.65)×10-6 (?cm)-1. © 2016 The Authors.
Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf¦CoFeB¦MgO structures
(Amer Inst Physics, 2016) Akyol, Mustafa; Jiang, Wanjun; Yu, Guoqiang; Fan, Yabin; Gunes, Mustafa; Ekicibil, Ahmet; Amiri, Pedram Khalili
We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure. Published by AIP Publishing.
Electronic transport in strained p-modulation Be-doped Ga0.8In0.2As/GaAs single quantum well
(Taylor & Francis Ltd, 2014) Gunes, Mustafa; Gumus, Cebrail
We report on the electronic transport properties of p-modulation Be-doped Ga0.8In0.2As/GaAs single quantum well. The experiments included the spectral photoluminescence between 8 and 300 K, and Hall effect measurements at temperatures between 14 and 300 K. The effect of strain which induces splitting of the valence band as light and heavy hole bands on transport is discussed. The calculated band alignment of the GaInAs sample using model-solid theory including strain effects indicates large conduction band discontinuities and a much smaller valance band discontinuity in GaInAs. The effect of the conduction and valance band discontinuity on the electronic transport properties is also discussed.
Magnetocaloric effect in (La1-xSmx)0.67Pb0.33MnO3 (0 ? x ? 0.3) manganites near room temperature
(Elsevier Science Sa, 2015) Cetin, Selda Kili; Acet, Mehmet; Gunes, Mustafa; Ekicibil, Ahmet; Farle, Michael
We present an investigation on structure, magnetic and magnetocaloric properties of the perovskite manganites (La1-xSmx)(0.67)Pb0.33MnO3 (x = 0, 0.1, 0.2, 0.3) synthesized by sol-gel technique. The XRD patterns show that all synthesized samples have reflections typical of the perovskite structure with orthorhombic symmetry. Thermomagnetic measurements showed that all the samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature decreases with increasing Sm content from 358 K for x = 0-286 K for x = 0.3. We determined the isothermal magnetic entropy changes of all the samples from the magnetization measurements and furthermore measured the adiabatic temperature change of the sample for x = 0.3 directly. The results showed that the adiabatic temperature change, determined using together the entropy change and the specific heat and the value obtained by direct temperature change measurements both give 1.3 K for a magnetic field change of 3 T at about 280 K. We also measured the cyclic adiabatic temperature-change of the sample and the results indicate that the sample undergoes a reversible temperature-change on field-cycling which is essential for magnetic refrigeration. (C) 2015 Elsevier B.V. All rights reserved.
Magnetocaloric properties of (La1-xPrx)0.85K0.15MnO3 (x=0.0, 0.1, 0.3 and 0.5) perovskite manganites
(Elsevier Sci Ltd, 2016) Akca, Gonul; Cetin, Selda Kılıç; Gunes, Mustafa; Ekicibil, Ahmet
In this study, we have investigated the effect of Pr on the structural, magnetic and magnetocaloric properties of La1-xPrx)(0.85)K0.15MnO3 (x=0.0, 0.1, 0.3 and 0.5) samples synthesized by sol-gel technique. The XRD patterns of samples for x=0.0 and 0.1 are indexed to rhombohedral structure with hexagonal setting (space group R (3) over barc) while the samples for x=0.3 and 0.5 crystallized in the orthorhombic structure with space group Pbnm. Magnetization measurements versus temperature in a magnetic field of 250 Oe indicate that all samples show a ferromagnetic to paramagnetic transition with increasing temperature. The Curie temperature, T-C, decreases with increasing Pr3+ concentration from 238 K for x=0.0-158 IC for x=0.5. We determined the magnetic entropy changes of the samples from M(H) isotherms that were measured around T-C. The values of maximum magnetic entropy change were found to be 4.63, 5.22, 2.80 and 2.30 J kg(-1) K-1 for x=0.0, 0.1, 0.3 and 0.5 for a field change of 2 T, respectively. For LPKM1 sample, we have also calculated the value of adiabatic temperature change as 3.11 K from the heat capacity and isothermal magnetization measurements under magnetic field of 2 T.
Magnetotransport study on as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs strained quantum well structures
(Springeropen, 2014) Donmez, Omer; Sarcan, Fahrettin; Erol, Ayse; Gunes, Mustafa; Arikan, Mehmet Cetin; Puustinen, Janne; Guina, Mircea
We report the observation of thermal annealing- and nitrogen-induced effects on electronic transport properties of as-grown and annealed n- and p-type modulation-doped Ga1-xInxNyAs1-y (x = 0.32, y = 0, 0.009, and 0.012) strained quantum well (QW) structures using magnetotransport measurements. Strong and well-resolved Shubnikov de Haas (SdH) oscillations are observed at magnetic fields as low as 3 T and persist to temperatures as high as 20 K, which are used to determine effective mass, 2D carrier density, and Fermi energy. The analysis of temperature dependence of SdH oscillations revealed that the electron mass enhances with increasing nitrogen content. Furthermore, even the current theory of dilute nitrides does not predict a change in hole effective mass; nitrogen dependency of hole effective mass is found and attributed to both strain- and confinement-induced effects on the valence band. Both electron and hole effective masses are changed after thermal annealing process. Although all samples were doped with the same density, the presence of nitrogen in n-type material gives rise to an enhancement in the 2D electron density compared to the 2D hole density as a result of enhanced effective mass due to the effect of nitrogen on conduction band. Our results reveal that effective mass and 2D carrier density can be tailored by nitrogen composition and thermal annealing-induced effects.
Physical properties of Cu2O thin films prepared by silar method
(Pamukkale Univ, 2017) Ozaslan, Dogan; Gunes, Mustafa; Gumus, Cebrail
Polycrystalline Cu2O thin films were obtained on glass substrates using by silar method at 70 degrees C. XRD analysis showed the films are a cubic structure and lattice parameters were calculated. The surface morphology of the films were imaged by FE-SEM (Field Emission Scanning Electron Microscope). In order to determine the optical properties of the Cu2O thin films UV/vis spectrophotometer was used. Optical transmittance (T%) values of the Cu2O films were determined in the wavelength range 300-1100 nm at room temperature. Semiconductor Cu20 of the thin films optical transmittance values were found to be 50-70% in the visible region. Energy band gap values (E-g) of the films were found to be 2.53-2.62 eV.
Structural and optical properties of diluted magnetic Ga1-xMnxAs-AlAs quantum wells grown on high-index GaAs planes
(Indian Acad Sciences, 2017) Gunes, Mustafa; Gumus, Cebrail; Gobato, Yara Galvao; Henini, Mohamed
We report on the structural and optical properties of Ga1-xMnxAs-AlAs quantum wells (QWs) with x = 0.1% grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates with orientations (100), (110), (311)B and (411)B. Atomic force microscopy (AFM), X-ray diffraction (XRD) and photoluminescence (PL) techniques were used to investigate these QWs. AFM results have evidenced the formation of Mn-induced islands, which are randomly distributed on the surface. These islands tend to segregate for samples grown on (110) and (411)B planes, while no clear segregation was observed for samples grown on (100) and (311)B orientations. Results show that the PL line width increases with Mn segregation. XRD measurements were used to determine 2 theta, d and cell parameters.
Synthesis of Mn-doped ZnS Thin Films by Chemical Bath Deposition: Optical Properties in the Visible Region
(Amer Inst Physics, 2017) Erken, Ozge; Gunes, Mustafa; Gumus, Cebrail
Transparent ZnS: Mn thin films were produced by chemical bath deposition (CBD) technique at 80 degrees C for 4h, 6h and 8h durations. The optical properties such as optical transmittance (T %), reflectance (R %), extinction coefficient (k) and refractive index (n) were deeply investigated in terms of contribution ratio, wavelength and film thickness. The optical properties of ZnS: Mn thin films were determined by UV/vis spectrophotometer transmittance measurements in the range of lambda= 300-1100 nm. Optical transmittances of the films were found from 12% to 92% in the visible region. The refractive index (n) values for visible region were calculated as 1.34-5.09. However, film thicknesses were calculated between 50 and 901 nm by gravimetric analysis.
Thermally activated flux mechanism in Mg-doped InN epitaxial film
(Taylor & Francis Ltd, 2017) Gunes, Mustafa; Akyol, Mustafa; Ekicibil, Ahmet; Tiras, Engin
The superconducting behaviour of InN has been observed in many experiments where the origin of superconductivity is addressed to presence of (i) In-In chains in ab-plane, (ii) specific carrier density range limited Mott transition critical carrier density and (iii) presence of In O-2(3) impurities. Although the superconductivity can be observed when the above conditions are enough for epitaxial grown InN films, the superconductivity properties of InN, so far, have not worked comprehensively. Here, we report the magneto-resistance, upper critical field and thermally activated flux mechanism of superconductor Mg doped InN epitaxial film grown by Molecular Beam Epitaxy. The superconducting phase transition temperature was observed at similar to 3.9 K at zero magnetic field. The carrier density of the film is found in the range of Mott transition and superconductivity to metal transition. The effect of magnetic field on the superconductivity of Mg-doped InN film is studied by employing the magnetoresistance and Hall resistance measurement with a typical Hall-bar shape device. The magnetoresistance analysis has been carried out by flux-flow and flux-creep models. The activation energy is found as highly sensitive with field in a range of 0.0 to 1.0 T. The upper critical field at zero temperature and coherence length estimated by Ginzburg-Landau relation were found as around 0.8 T and 216.9 angstrom, respectively. The superconducting properties of the epitaxial growth Mg-doped InN film are discussed through the manuscript.

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