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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 Capacitance-conductance-frequency characteristics of Au/Ni/n-GaN/undoped GaN Structures(ELSEVIER SCIENCE BV, 2015) Dogan, Hulya; Yildirim, Nezir; Orak, Ikram; Elagoz, Sezai; Turut, AbdulmecitFrequency-dependent capacitance (C) and conductance (C) characteristics of the Au/Ni/n-GaN/undoped GaN device have been investigated in the reverse bias voltage range of 0.00-0.40 V. The GaN films have been epitaxially grown by metal organic chemical vapor deposition on c-plane Al2O3 substrate. The measurement frequency (f) ranges from 1.0 kHz to 10 MHz. The slow and fast interface states with two time constants differing by about two orders of magnitude have been calculated from analysis of the reverse bias C-f and C-f characteristics. The interface state density has values of 10(10)-10(11) eV(-1) cm(-2) and time constant has taken the values which change in range of 10(-5)-10(-7) s. The phase angle versus bias voltage curves have shown at four different frequencies at the room temperature that the device behaves more capacitive at the reverse bias region rather than the forward bias region at 100 and 200 kHz. (C) 2014 Elsevier B.V. All rights reserved,Öğe Çift GaAlAs/GaAs ve GaInAs/GaAs kuantum kuyularının kuyu genişliğine bağlı olarak elektronik özellikleri(Sivas Cumhuriyet University, 2019) Ozturk, Ozan; Ozturk, Emine; Elagoz, SezaiBu çalışmada, çift Ga1-x Alx As/GaAs kuantum kuyularının (A yapısı) ve Ga1-x Inx As/GaAs /GaAs kuantum kuyularının (B yapısı) elektronik özellikleri kuyu genişliğine bağlı olarak incelenmiştir. Etkin kütle yaklaşımı kullanılarak, Schrödinger denkleminin çözümüyle enerji seviyeleri, dalga fonksiyonları ve bu sistemin olasılık yoğunlukları hesaplanmıştır. Elde edilen sonuçlara göre, A ve B yapısının temel farklılıkları yasak enerji aralığı ve etkili kütledir. A yapısı için engel GaAlAs ve kuyu GaAs’dır. B yapısı için ise engel GaAs ve kuyu GaInAs’dır. Ayrıca, A yapısının potansiyel yüksekliği ve enerji seviyeleri her zaman B yapısından düşüktür. Kuyu genişliği, çift kuantum kuyusunun (DQW) elektronik özellikleri üzerinde büyük bir etkiye sahiptir. Bu özellikler, ayarlanabilir yarı iletken cihazların tasarımı için pratik bir ilgiye sahiptir.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 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 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 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 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 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 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, RamazanZnO 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.Öğe Temperature-dependent electrical transport properties of (Au/Ni)/n-GaN Schottky barrier diodes(ELSEVIER SCIENCE BV, 2014) Dogan, Hulya; Elagoz, SezaiThe temperature-dependent electrical properties of (Au/Ni)n-GaN Schottky barrier diodes (SBDs)have been investigated in the wide temperature range of 40-400 K. The analysis of the main electrical characteristics such as zero-bias barrier height (Phi(B0)), ideality factor (n) and series resistance (R-s) were found strongly temperature dependent. Such behavior is attributed to barrier inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the interface. It is evident that the diode parameters such as zero-bias barrier height increases and the ideality factor decreases with increasing temperature. The values of series resistance that are obtained from Cheung's method are decreasing with increasing temperature. The temperature dependence of Schottky barrier height (SBD) and ideality factor (n) are explained by invoking three sets of Gaussian distribution of (SBH) in the temperature ranges of 280-400 K. 120-260 K and 40-100 K. respectively. (Au/Ni)/n-GaN Schottky barrier diode have been shown a Gaussian distribution giving mean BHs (Phi) over bar (B0)) of 1.167, 0.652 and 0.356 eV and standard deviation sigma(s) of 0.178, 0.087 and 0.133 V for the three temperature regions. A modified In(I-0/T-2) q(2)sigma(2)/2k(2)T(2) vs. 1/kT plot have given (Phi) over bar (B0) and A* as 1.173 eV and 34.750 A/cm(2) K-2, 0.671 eV and 26293 A/cm(2) K-2, 0.354 eV and 10.199 A/cm(2) K-2, respectively. (C) 2014 Elsevier B.V. All rights reserved.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.
