Yazar "Demir, Ilkay" seçeneğine göre listele
Listeleniyor 1 - 18 / 18
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe AlGaN/AlN MOVPE heteroepitaxy: pulsed co-doping SiH4 and TMIn(Iop Publishing Ltd, 2019) Demir, Ilkay; Kocak, Yusuf; Kasapoglu, A. Emre; Razeghi, Manijeh; Gur, Emre; Elagoz, SezaiWe report a new growth approach pulsed co-doping growth of AlxGa1-xN (x > 0.5) epilayers on AlN/Al2O3 templates by metal organic vapor phase epitaxy (MOVPE). Using this approach SiH4 (silane) and TMIn (trimethylindium) supplied to the growth chamber alternately and pulsed during the growth of AlGaN epilayers. Structural and morphological quality of AlGaN epilayers were investigated by high resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), Raman spectroscopy, and scanning electron microscopy (SEM) techniques. It has shown that higher crystalline quality with low full width at half maximum (FWHM) and smoother surface morphology with reduced hexagonal hillock density has been obtained by the pulsed codoping growth approach. Volcano like hillock structures has been confirmed by Raman mapping.Öğe Close oxygen coupled low-pressure chemical vapor deposition growth of high quality ? - Ga2O3 on sapphire(Elsevier Sci Ltd, 2022) Akyol, Fatih; Demir, IlkayWe report on the close oxygen coupled low-pressure chemical vapor deposition (COC-LPCVD) hetero-epitaxial growth of atomically smooth (-201) oriented beta-Ga2O3 on c-plane sapphire. Utilizing a dedicated line within the main tube, O-2 could be delivered to the substrate surface which enables effective control of growth regime. Under optimized conditions (Ga-rich and near stoichiometric feed rate), step flow growth was obtained with X-ray rocking curve full-width at half maximum of 0.09 degrees and 0.20 degrees at a growth rate of 0.49 mu m/h and 3.42 mu m/h, respectively. On the other hand, oxygen-rich growth at high growth rates produced in-plane rotational domains. In addition, the alignment of single crystal (-201) beta-Ga2O3 with respect to the sapphire offcut direction was revealed such that [-20-1] beta-Ga2O3 is along [11-20] (offcut direction) sapphire. This study demonstrates the potential of the versatile COC-LPCVD system on the thin film growth of high quality beta-Ga2O3.Öğe 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, SezaiWe 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.Öğe The contribution of AsH3: Pre-flow and V/III ratio effects on heteroepitaxially grown GaAs/Ge(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2019) Demir, IlkayWe report the effects of AsH3 (arsine) on morphological, structural, optical and crystalline quality of MOVPE (metal organic vapor phase epitaxy) grown GaAs/Ge heterostructures. AsH3 pre-flow supplied on Ge substrate to have As atoms as a first atomic layer on the surface of Ge substrate. Additionally, the V/III ratio effects of LT-GaAs buffer layer, grown on arsenized Ge substrate, have been analyzed to have reduced APBs (anti-phase boundaries) in the interface between epilayer and Ge substrate. It has been considered that the optimal AsH3 pre-flow duration and V/III ratio of GaAs buffer layer extremely influence the effects of APBs even we have used miss-cut Ge substrate and grown by two-step growth technique to obtain double atomic step. It is shown that without AsH3 pre-flow the surface of GaAs epilayer becomes rougher while it is optically smooth under the longer AsH3 pre-flow. On the other hand, even the surface situation does not change with longer AsH3 pre-flow the structural, optical and crystalline qualities become worse because of the possible presence vacancies of created during the growth. Similar behavior has been observed for the V/III effects of GaAs buffer layer and it has resulted in low full width at half maximum of high-resolution X-ray diffraction and high photoluminescence peak intensity for the optimal V/III ratio.Öğe Direct growth of thick AlN layers on nanopatterned Si substrates by cantilever epitaxy(WILEY-V C H VERLAG GMBH, 2017) Demir, Ilkay; Robin, Yoann; McClintock, Ryan; Elagoz, Sezai; Zekentes, Konstantinos; Razeghi, ManijehAlN layers have been grown on 200 nm period of nano-patterned Si (111) substrates by cantilever epitaxy and compared with AlN layers grown by maskless lateral epitaxial overgrowth (LEO) on micropatterned Si (111) substrates. The material quality of 5-10 mu m thick AlN grown by LEO is comparable to that of much thinner layers (2 mu m) grown by cantilever epitaxy on the nanopatterned substrates. Indeed, the latter exhibited root mean square (RMS) roughness of 0.65 nm and X-ray diffraction full width at half-maximum (FWHM) of 710 arcsec along the (0002) reflection and 930 arcsec along the (10-15) reflection. The corresponding room temperature photoluminescence spectra was dominated by a sharp band edge peak. Back emission ultra violet light emitting diodes (UV LEDs) were fabricated by flip chip bonding to patterned AlN heat sinks followed by complete Si (111) substrate removal demonstrating a peak pulsed power of similar to 0.7mW at 344 nm peak emission wavelength. The demonstrated UV LEDs were fabricated on a cost effective epitaxial structure grown on the nanopatterned Si substrate with a total thickness of 3.3 mu m. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimÖğe Effect of Si-doped and undoped inter-layer transition time on the strain-compensated InGaAs/InAlAs QCL active region grown with MOVPE(Elsevier B.V., 2023) Perkitel, Izel; Demir, IlkayIn this study, we report the effect of the combination of Si-doped and undoped inter-layer transition time in the strain compensated In0.67Ga0.33As/In0.36Al0.64As quantum cascade laser (QCL) structure grown on InP substrate by Metal Organic Vapor Phase Epitaxy (MOVPE). In situ reflectance spectroscopy and high resolution X-ray diffraction (HRXRD) technique have been used for the analysis of growth steps and crystalline quality of QCL structures, respectively. In addition, since thickness accuracy is very important for QCLs, two different thickness calculation methods have been used in the Global Fit simulation program for detailed thickness accuracy of structures. As a result, optimum values for thickness accuracy have been obtained as 5 and 10 s between undoped and Si-doped layers, respectively, as verified by the two methods. © 2022 Elsevier B.V.Öğe 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, SezaiThe 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.Öğe Experimental insights toward carrier localization in in-rich InGaAs/InP as candidate for SWIR detection: Microstructural analysis combined with optical investigation(Elsevier Ltd, 2023) Ben Arbia, Marwa; Demir, Ilkay; Kaur, Navpreet; Saidi, Faouzi; Zappa, Dario; Comini, Elisabetta; Altuntaş, IsmailHyperspectral imaging has been flourished thanks to the huge investigation of the infrared spectrum from NIR to LWIR bands. The ternary InGaAs has been investigated herein in the context of studying the structural dependences of localization phenomenon by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Raman, ultraviolet–visible (UV–vis), and photoluminescence (PL) techniques. Using metal-organic vapor phase epitaxy (MOVPE), we succeed to grow the InGaAs directly on InP substrate at 560 °C as an active layer with indium concentration exceeding the “golden” value (53%) to enlarge its cutoff absorption wavelength. X-ray diffraction proved a good crystallinity of the heterostructure with a sharp peak related to the thick substrate and another peak attributed to the thin layer of InGaAs. Moreover, an interfacial layer appeared at the logarithmic scale of XRD patterns and was confirmed by Raman analysis. The SEM-EDX revealed an average indium concentration (62%), almost the growth concentration. However, a cross-section compositional profile over the heterostructure showed an inhomogeneous distribution of the indium. This is predictable from the composition fluctuation in the indium-containing alloys and the volatility (surface segregation) of As (In). On the other side, the optical investigation of InGaAs demonstrated an anomalous behavior of luminescence versus temperature, manifested by the S-shape feature. This trend stems from the potential fluctuation induced by the non-uniform distribution of indium. A numerical simulation was developed based on the localized state ensemble (LSE) model to well-reproduce this anomaly by giving the best fitting parameters and comparing them with those calculated using the semi-empirical models (Viña and Pässler). The results reported here will help in optimizing the epitaxy design of future InGaAs/InP and further studying its surface morphology and device performance. © 2022Öğe Growth of InGaAs/InAlAs superlattices by MOCVD and precise thickness determination via HRXRD(GAZI UNIV, 2016) Demir, Ilkay; Elagoz, SezaiIn this study, we report the growth studies of InGaAs/InAlAs superlattices (SLs) with thin layer thicknesses which will be used for quantum cascade laser (QCL) structures, grown by Metal Organic Chemical Vapor Deposition (MOCVD) technique. We utilize high resolution X-ray diffraction (HRXRD) to determine the single layer thickness and period thicknesses of SLs. Measurement results show that by establishing very low growth rates (similar to 0,1 nm/s), the single thin layers and SLs can be grown well by MOCVD in a controllable and repeatable way with high crystalline and interface quality.Öğe High brightness ultraviolet light-emitting diodes grown on patterned silicon substrate(ELSEVIER SCI LTD, 2019) Robin, Yoann; Ding, Kai; Demir, Ilkay; McClintock, Ryan; Elagoz, Sezai; Razeghi, ManijehWe report on the fabrication of high brightness AlGaN-based ultraviolet light emitting diodes (UV-LED) on patterned silicon. Using the lateral epitaxial overgrowth approach, we demonstrate the growth of a 6 mu m thick AIN layer of high crystalline quality. X-ray diffraction characterization showed a rocking curve with a full width at half maximum of 553 and 768 '' for the (00.2) and (10.2) planes, respectively. The low dislocation density of the AIN template enabled the growth of bright AlGaN/GaN quantum wells emitting at 336 nm. By appropriate flip-chip bonding and silicon substrate removal processing steps, the patterned AIN surface was exposed and efficient bottom-emission UV-LEDs were realized. Improvement of the AIN quality and the structure design allowed the optical output power to reach the milliwatt range under pulsed current, exceeding the previously reported maximum efficiency. Further investigations of the optical power at different pulsed currents and duty cycles show that thermal management in this device structure is still challenging, especially in continuous wave mode operation. The strategy presented here is of interest, since AIN crystalline quality improvement and optimization of the light extraction are the main issues inhibiting efficient UV emitter on silicon fabrication.Öğe 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, IlkayCarbon (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.Öğe Influences of thickness and temperature of low temperature GaAs buffer layer on two-step MOVPE grown GaAs/Ge heterostructures(Edp Sciences S A, 2020) Demir, Ilkay; Kasapoglu, Ahmet Emre; Budak, Hasan Feyzi; Gur, Emre; Elagoz, SezaiWe investigate influence of GaAs buffer layer (BL) growth parameters such as temperature and thickness on the structural, morphological, crystalline and optical quality of metal organic vapor phase epitaxy (MOVPE) grown heterostructures of GaAs on Ge. It was found that the optimal BL conditions significantly decrease the effects of anti-phase boundaries (APBs) even when grown on offcut Ge substrate by two-step growth technique with AsH3 pre-flow to promote double atomic step formation. It is observed that as the growth temperature increases, the growth rate of the GaAs BL increases, too. Improvement on the structural quality is observed up to BLs temperature of 535 degrees C, then it decreases. On the other hand, as the different thick BLs, 12, 25, 75nm are considered, the epilayer grown on the 25nm thick BL has shown the lowest full width at half maximum (FWHM) value, large photoluminescence peak intensity and internal quantum efficiency (IQE).Öğe InGaAs-Based MSM Photodetector: Researching Absorption Layer, Barrier Layer, and Digital Graded Superlattice Layer with 3D Simulation(Elsevier, 2023) Unal, Dudu Hatice; Demir, IlkayThe effects of absorption, barrier, and digital graded layer thickness on dark current and photocurrent in Metal Semiconductor Metal (MSM) photodetectors by using 3D Silvaco TCAD are reported. The photo-dark current ratio (Iphoto/Idark) is calculated using the photocurrent and dark current values obtained by simulation. In study A (absorption layer thickness variation) the photocurrent, dark current and photo-dark current ratio are increased with increased absorption layer thickness, and the dark current is 1.138x10-7 A levels. In Study B (barrier layer thickness variation), when the barrier layer is added to the absorption layer, the dark current is decreased to 1.56x10-11 A levels. It is reported that the photo-dark current ratio with increasing barrier layer thickness increases. In study C (digital graded superlattice layer thickness variation), the dark current increases, and photocurrent decreases with the increase of the digital graded superlattice layer thickness. However, the photodark current ratio with increasing digital graded superlattice layer thickness decreases. Furthermore, a similar trend of development is observed on photo-dark current with adding of the barrier layer and digital graded superlattice layer on the absorption layer. These findings demonstrate the importance of optimizing layer thickness in MSM photodetectors for improved device performance.Öğe Interruption time effects on InGaAs/InAlAs superlattices of quantum cascade laser structures grown by MOCVD(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2016) Demir, Ilkay; Elagoz, SezaiWe report the growth of high quality InGaAs/InAlAs quantum cascade laser (QCL) structure which composed of superlattices (SLs) and the effects of interruption time between each layer of the SL structure. Inserting an interruption delay during the growth dramatically effects the quality of the SL as indicated by crystallinity, interface sharpness and optical properties. The results show that an increase in interruption time up to a certain value makes sharper interfaces and improves optical and structural properties, but, beyond that value, overall quality starts to degrade. The composition and the growth rate of each single thin layer are determined by using high resolution X-ray diffraction (HRXRD) measurements. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Real, imaginary and complex branches of Lamb waves in p-type piezoelectric semiconductor GaAs plate: Numerical and experimental investigation(Elsevier Sci Ltd, 2024) Dhib, Abderrahmen; Njeh, Anouar; Othmani, Cherif; Takali, Farid; Ben Salah, Issam; Demir, Ilkay; Zhang, BoFirst, we experimentally measure the concentration of holes of the piezoelectric semiconductor (PSC) Gallium arsenide (GaAs) material based on the Hall effect measurement. We then numerically calculate the Lamb wave characteristics in a p-type PSC GaAs plate using this measured value of the concentration of holes (estimated at approximately p0 = 3.5431 x 1025m- 3). To guarantee the coupling effect that makes the Lamb wave a piezoactive wave, the GaAs crystal is oriented in a specific orientation of (110) plane. Ordinary differential equation (ODE) method is employed to calculate the dispersion curves, 3D view of the mechanical displacements, 3D view of the electric potential and 3D view of the concentrations of holes. Results show that the appearance of the complex branches of the Lamb modes coincides with the vanishing of the imaginary part of the wavevector (Im(k1)) to zero, which is a very remarkable finding that has not been discussed in previous studies. Meanwhile, these complex branches start exactly at the point of Zero-group-velocity (ZGV). Moreover, the present work highlights the hole drift characteristics of PSC GaAs and provides a critical comparative discussion with those published by (Zhu et al., 2018) for the PSC ZnO plate. Accordingly, the Screening effect phenomenon that is based on the positive holes in the negative electric potential region is discussed. The present results provide a theoretical and fundamental guidance on the development of smart devices based on the PSC GaAs material.Öğe 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. ÖzgürIn 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.Öğe 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, IlkayIn 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.Öğe V/III ratio effects on high quality InAlAs for quantum cascade laser structures(ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2017) Demir, Ilkay; Elagoz, SezaiIn this study we report the VIII ratio effects on growth, structural, optical and doping characteristics of low growth rate (similar to 1 angstrom/s) heteroepitaxial Metal Organic Chemical Vapor Deposition (MOCVD) grown In(x)A(1-x)As layers, a part of Quantum Cascade Laser (QCL) structures, on InP substrate. Especially photoluminescence (PL) properties of InAlAs-InP interface show strong dependence on AsH3 overpressure. We have shown that the VIII ratio with fixed metalorganic precursor flow is a crucial parameter on In In(x)A(1-x)As layers to have a good material quality in terms of crystallinity, optical and electrical characteristics with and without doping. (C) 2017 Elsevier Ltd. All rights reserved.
