Yazar "Altuntas, Ismail" seçeneğine göre listele

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    Comprehensive growth and characterization study on highly n-doped InGaAs as a contact layer for quantum cascade laser applications
    (IOP PUBLISHING LTD, 2018) Demir, Ilkay; Altuntas, Ismail; Bulut, Baris; Ezzedini, Maher; Ergun, Yuksel; Elagoz, Sezai
    We present growth and characterization studies of highly n-doped InGaAs epilayers on InP substrate by metal organic vapor phase epitaxy to use as an n-contact layer in quantum cascade laser applications. We have introduced quasi two-dimensional electrons between 10 s pulsed growth n-doped InGaAs epilayers to improve both carrier concentration and mobility of structure by applying pulsed growth and doping methods towards increasing the Si dopant concentration in InGaAs. Additionally, the V/III ratio optimization under fixed group III source flow has been investigated with this new method to understand the effects on both crystalline quality and electrical properties of n-InGaAs epilayers. Finally, we have obtained high crystalline quality of n-InGaAs epilayers grown by 10 s pulsed as a contact layer with 2.8 x 10(19) cm(-3) carrier concentration and 1530 cm(2) V-1 s(-1) mobility.
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    The effects of two-stage HT-GaN growth with different V/III ratios during 3D-2D transition
    (IOP PUBLISHING LTD, 2018) Altuntas, Ismail; Demir, Ilkay; Kasapoglu, Ahmet Emre; Mobtakeri, Soheil; Gur, Emre; Elagoz, Sezai
    The aim of the study is to understand the effects of two stages of HT-GaN growth with different V/III ratios on optical, chemical and structural characteristics of the HT-GaN layer. In addition, the effects of two-stage growth on the transport properties has been presented through fabricated Schottky diodes. As the V/III ratio in the 1st stage growth of HT-GaN layer is varied, it has been observed that recovery of reflectance is faster with higher V/III ratios, while no significant effect has been observed by changing the V/III ratios in the 2nd stage of HT-GaN growth. The 2nd stage growth is caused to decrease in screw dislocation densities obtained from the high-resolution x-ray diffraction measurements. The lowest edge type dislocation densities have been obtained for samples with lower V/III ratios in both the 1st and 2nd stages of HT-GaN growth. Well-defined terraces and a few GaN atomic layer surface roughness have been realized through the atomic force microscopy measurements on all the samples. Ga atom bound oxygen states has been investigated through the x-ray photoelectron spectroscopy to find out the V/III ratio effect on the impurity incorporation. An increase in the V/III ratio has given rise to a higher percentage of oxygen incorporation during the 2nd stage of growth. The lowest internal quantum efficiency has been obtained for the samples grown at the highest V/III ratio for both the 1st and 2nd growth stages. Fine excitonic transitions have been indicated by the low temperature high-resolution photoluminescence measurements. Current-voltage measurements performed on the Schottky diodes have shown the effects on the diode parameters.
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    Influence of Highly Efficient Carbon Doping on AlxGa1-xAs Layers with Different Al Compositions (x) Grown by MOVPE
    (Springer, 2023) Perkitel, Izel; Kekul, Reyhan; Altuntas, Ismail; Gur, Emre; Demir, Ilkay
    Carbon (C)-doped aluminum gallium arsenide (AlxGa1-xAs) epitaxial layers with different aluminum (Al) concentrations have been grown on gallium arsenide (GaAs) substrates by metalorganic vapor phase epitaxy (MOVPE) technique. The impact of varying carbon tetrabromide (CBr4) flow rates on the electrical properties of AlxGa1-xAs materials with different Al compositions has been investigated. High-resolution x-ray diffraction (HRXRD) measurement and a Hall effect measurement system have been used to determine the Al compositions and to evaluate the electrical properties. It has been found that the carrier density increases and the mobility decreases by increasing the flow rate of CBr4 and changing Al compositions up to a certain point. In contrast, at higher Al compositions, a decrease in carrier density and an increase in mobility have been observed with increasing CBr4 flow rate. Since these observed trends require to be analyzed in more detail, x-ray photoelectron spectroscopy (XPS) has been used to analyze the elements in the structure. From the XPS results, it has been shown that the atomic concentration of the arsenic in the structure decreased with the increase in CBr4 flow rates. In addition, it has been shown that the Al composition in the AlxGa1-xAs material obtained from the XRD results increases with the increase in the atomic concentration of the arsenic. Accordingly, a linear increase in carrier concentration is shown with increasing Al composition. This increase is explained by the effect of the Al-C bond content on the electrical properties of Al(x)Ga(1-)xAs.
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    Sputtered AlN for Distributed Bragg Reflectors Operating in the SWIR Wavelengths
    (Optica Publishing Group (formerly OSA), 2022) Kaynar, Emine; Hopoglu, Hicret; Altuntas, Ismail; Demir, Ilkay; Sayraç, Muhammed; Tüzemen, Ebru S.; Alaydin, B. Özgür
    In this study, we aim to eliminate low thermal conductivity and refractive index differences in InP and GaSb based materials, which result in low output power and limited operation wavelength range for VECSELs. © 2022 OSA - The Optical Society. All rights reserved.
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    Structural and electrical properties of nitrogen-doped ZnO thin films
    (ELSEVIER SCIENCE BV, 2014) Tuzemen, Ebru Senadim; Kara, Kamuran; Elagoz, Sezai; Takci, Deniz Kadir; Altuntas, Ismail; Esen, Ramazan
    ZnO and nitrogen-doped ZnO thin films were prepared onto glass substrate by pulsed filtered cathodic vacuum arc deposition (PFCVAD) system at room temperature. The influence of doping on the structural, electrical and optical properties of thin films was investigated. XRD studies were carried out to analyze and compare the structural quality of undoped and nitrogen-doped ZnO films. Raman measurement was performed to study the doping effects in the ZnO. The optical transmittances of all films are studied as a function of wavelength using UV-VIS-NIR spectrophotometer. The optical band gap values of the films are found using absorbance spectrums. The electrical studies for the films are carried out by using Hall-effect measurements. (C) 2014 Elsevier B.V. All rights reserved.
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    The Effect of Si (111) Substrate Surface Cleaning on Growth Rate and Crystal Quality of MOVPE Grown AlN
    (Gazi Univ, 2022) Perkitel, Izel; Altuntas, Ismail; Demir, Ilkay
    In this work, the effect of Si (111) substrate surface cleaning by RCA (Radio Corporation of America) method on growth rate and crystalline quality of epitaxially grown AlN thin films by MOVPE (Metal Organic Vapor Phase Epitaxy) technique is investigated. In situ reflectance system and high resolution X-ray diffraction (HRXRD) technique are used for the analysis of growth rate and crystal quality of epitaxial AlN layers, respectively. Also, The Raman measurement is done to show the effect of the RCA cleaning procedure on the position of the peaks that occurred in the Raman spectra. The results have shown that the surface cleaning of Si (111) substrate by the RCA method removes the oxide layer formed on the surface, also helps to decrease the parasitic reactions and increases the adatom efficiency, results in an increased growth rate of the AlN layer. Besides, surface cleaning of Si (111) substrate by the RCA method has reduced the FWHM value similar to 5% for omega-2 theta scan and similar to 60% for omega scan of AlN epilayer, indicating an improvement in crystal quality.