Investigation Of InxGa1-xN (x= 0,075; 0,090; 0,100) Blue Led's Microstructure Defects From Reciprocal Space Mapping

Bu tezde, InxGa1-xN (x= 0,075; 0,090; 0,100) temelli mavi ışık yayan diyot (LED) yapısı çalışıldı. Öncelikle n-GaN ve p-AlGaN+GaN kontak arasında, c-yönelimli safir alttaş üzerine metal organik kimyasal buhar biriktirme (MOCVD) yöntemi ile InGaN/GaN çoklu kuantum kuyu (MQW) LED yapısı büyütüldü. Örnek büyütme aşamasında tüm örnekler için InGaN tabakanın büyütme sıcaklığı dışındaki basınç ve kaynak akı oranları gibi tüm parametreleri sabit tutuldu. Farklı In oranlarındaki InGaN/GaN ışık yayan diyot örneklerin; yapısal, optiksel, elektriksel ve morfolojik özellikleri, Yüksek Çözünürlüklü X-Işını Kırınımı (HRXRD), Atomik Kuvvet Mikroskobu (AFM), Fourier Kızılötesi Spektroskopisi (FTIR), Fotolüminesans (PL) ve Akım-Gerilim Karakteristiği (I-V) teknikleri ile incelendi. Yüksek Çözünürlüklü X-Işını Kırınımı Tekniği kullanılarak yapı kusurlarının araştırılması için ters örgü uzayı haritası çıkarıldı. GaN epitaksiyel yapının özellikleri referans alınarak, InGaN ve AlGaN tabakanın nokta kusurları (örgü rahatlaması, örgü zorlaması, üç yönlü zorlama ve iki yönlü zorlama) ve mozaik yapı kusurları (eğim açısı, yanal ve dikey mozaik kristal boyut, vida ve kenar dislokasyon yoğunluğu) hesaplandı. Yüzey pürüzlülük parametrelerinin, büyütme sıcaklığına bağlı olarak araştırması yapıldı. Tüm yapısal kusurların, büyütme sıcaklığı ile değiştiği ters örgü uzayı haritalaması ile net bir şekilde görüldü. Ayrıca LED yapıların AlGaN tabakasındaki nokta kusurları InGaN tabaka ile kıyaslandı. Her iki tabakanın rahatlama yüzdeleri birbirine göre ters davranış gösterirken, hidrostatik ve iki yönlü zorlama değişimleri her iki tabaka içinde benzer özellikler gösterdi. Sonuç olarak bir tabakadan diğer tabakaya nokta ve çizgi kusurların taşınması nedeniyle aynı tip kusur eğilimleri görüldü. Değişen In oranı değerlerinde elde edilen mozaik yapı kusurları, InGaN aktif tabakası için uygun büyütme sıcaklığını ortaya koydu. 667 oC olan bu büyütme sıcaklığında: AFM analizlerine göre LED yapının, yüksek kristal boyutlu ve pürüzlü, PL ve FTIR sonuçlarına göre yasak band enerji aralığının ve dalgaboyunun maviye kaydığı ve titreşim enerji piki yarı genişliğinin azaldığı, I-V ölçümlerine göre LED'in ışığa karşı tepki verdiği görüldü. Nihai olarak InGaN MQW mavi LED'lerin tüm analiz sonuçlarının birbirlerini desteklediği ve 667 oC'nin LED üretimi için optimum büyütme sıcaklığı olduğu anlaşıldı.In this thesis, The microstructure of InxGa1-xN (x= 0,075; 0,090; 0,100) blue light emitting diodes (LED) were investigated. First, LED structures with InGaN/GaN multiple quantum wells (MQW) were grown between n-GaN and p-AlGaN+GaN contacts using metal organic chemical vapor deposition (MOCVD) on c-oriented sapphire substrates. The process parameters, such as the pressure and source flow rates, were kept constant with the exception of growth temperature of the InGaN layers. Then, the structural, optical, electrical and surface morphologic properties of InGaN/GaN LED samples with different Indium content were characterized using High-Resolution X-Ray Diffraction (HRXRD), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR), Photoluminescence (PL) and Current-Voltage (I-V) Characteristics. To examine the structural defects in crystal forms, a reciprocal lattice space was mapped using a High Resolution X-Ray Diffractometer. The point defects (lattice relaxation, lattice strain, hydrostatic strain, biaxial strain) and mosaic structure defects (the tilt angles, lateral and mosaic crystal dimension of mosaic blocks, screw and edge dislocation densities) of GaN and InGaN layers were estimated by taking the structure properties of GaN epitaxial layer as the reference. Furthermore, the relationship between the parameters of surface roughness and the growth temperature were examined. The changes in structural defects with respect to the growth temperature were observed using reciprocal space mapping. Additionally, the point defects of the blue LED structure on AlGaN layer were compared to those of InGaN layer. While the relaxation percent of both layers were opposite to each other; hydrostatic and biaxial strain changes showed the same properties for both layers. The defect types were showing similar trends in both structures, because the same type of point defects and line defects were extended from one layer to the other. The changing ratio of mosaic structure defects with respect to the Indium content revealed the optimized growth temperature for the InGaN active layers. The following specifc observations were made at the optimized growth temperature of 667 oC: The AFM analysis revealed that the LED structures were high crystal size and rough. According to PL and FTIR results, the band gap energy and wavelengths shifted towards the blue spectrum and the half-width of vibrational energy peak decreased. According to the I-V measurements, LED structure was responsive to the light. Finally, it was concluded that all the analysis results of the InGaN MQW blue LEDs were consistent and supported each other, and 667 OC was found to be the optimized growth temperatures for LED fabrication

Organizational Learning on Coopetition Strategy: An Exploratory Research on a Turkish Private Bank's Credit Card Application

For this purpose, semi structured interviews were made with the managers of operation and information technology departments in the bank which has applied coopetition to increase its credit card market share in the Turkish banking sector since 2007. With these interviews, the effect of coopetition on organizational learning has been explored. On the other hand the importance of documentation and communication on organizational learning, the effect of coopetition on people, information system and organizational process of the bank were also explored in this study

Microstructural Analysis with Graded and Non-Graded Indium in InGaN Solar Cell

In this study are graded and non graded InGaN/GaN samples grown on c-oriented sapphire substrate using the Metal Organic Chemical Vapour Deposition (MOCVD) technique. The structural and morphological properties of the grown InGaN/GaN solar cell structures are analyzed using High Resolution X-ray Diffraction (HRXRD), atomic force microscopy (AFM). Each structures c and a lattice parameters strain, biaxial strain, hydrostatic strain, stress, lattice relax, tilt angle, mosaic crystal size, dislocation densities of GaN and InGaN layers are determined by XRD measurements. In accordance with these calculations, the effect of graded structure on the defects, are discussed. As a dramatic result; although values of full width at half maximum (FWHM) are broad, a considerable decrease at dislocations is noticed. The AFM observations have revealed that the two dimensional growth of the graded sample is more significant and its roughness value is lower. JV measurements shown that the performance of the graded structure is higher. It is determined that all test results are consistent with each other

Examination of the temperature related structural defects of InGaN/GaN solar cells

In this study the effects of the annealing temperature on the InGaN/GaN solar cells with different In-contents grown on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) are analyzed by High Resolution X-ray Diffraction (HRXRD) and an Atomic Force Microscope (AFM). The plane angles, mosaic crystal sizes, mixed stress, dislocation intensities of the structure of the GaN and InGaN layers are determined. According to the test results, there are no general characteristic trends observed due to temperature at both structures. There are fluctuating failures determined at both structures as of 350 degrees C. The defect density increased on the GaN layer starting from 350 degrees C and reaching above 400 degrees C. A similar trend is observed on the InGaN layer, too. (C) 2015 Elsevier Ltd. All rights reserved.DPTHAMITTurkiye Cumhuriyeti Kalkinma Bakanligi; DPT-FOTONTurkiye Cumhuriyeti Kalkinma Bakanligi; TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [113E331, 109A015, 109E301]; [NATO-SET-193]This work is supported by the projects DPTHAMIT, DPT-FOTON, NATO-SET-193 and TUBITAK under Project Nos. 113E331, 109A015 and 109E301.WOS:0003626031000452-s2.0-8493884290

Sex-dependent colonic microbiota modulation by hazelnut (Corylus avellana L.) dietary fiber

Although many efforts have been made to characterize the functional properties of hazelnut constituents (mainly its oil, protein, and phenolics), those of its dietary fiber (DF) have not been elucidated yet. Here, we aimed to investigate the impact of DF of natural and roasted hazelnuts, and hazelnut skin on the colonic microbiota in vivo (C57BL/6J mouse models) by determining their composition through 16S rRNA sequencing and microbial short-chain fatty acids (SCFAs) using gas chromatography. Our results revealed that hazelnut DF generally showed an acetogenic effect in male mice, whereas the same trend was not observed in the female counterparts. The 16S rRNA sequencing results showed that hazelnut DF, especially that of natural hazelnuts, increased the relative abundances of Lactobacillus-related OTUs that have probiotic potential. LEfSe analysis indicated that, for female mice, Lachnospiraceae, Prevotella, Ruminococcaceae, and Lactobacillus were found to be discriminators for DF of natural hazelnuts, roasted hazelnuts, hazelnut skin, and control, respectively, whereas Bacteroides, Lactobacillus, Prevotella, and Lactococcus were the discriminators for the male counterparts, respectively. This study clearly indicates that, although the roasting process slightly alters the functionalities, hazelnut DF favors beneficial microbes and stimulates beneficial microbial metabolites in the colon in a sex-dependent way, which could be a contributing factor to the health-promoting effects of hazelnuts. Furthermore, hazelnut skin, a byproduct of the hazelnut industry, was found to have potential to be utilized to produce functional DF targeting colonic health

Clinical and molecular evaluation of MEFV gene variants in the Turkish population: a study by the National Genetics Consortium

Familial Mediterranean fever (FMF) is a monogenic autoinflammatory disorder with recurrent fever, abdominal pain, serositis, articular manifestations, erysipelas-like erythema, and renal complications as its main features. Caused by the mutations in the MEditerranean FeVer (MEFV) gene, it mainly affects people of Mediterranean descent with a higher incidence in the Turkish, Jewish, Arabic, and Armenian populations. As our understanding of FMF improves, it becomes clearer that we are facing with a more complex picture of FMF with respect to its pathogenesis, penetrance, variant type (gain-of-function vs. loss-of-function), and inheritance. In this study, MEFV gene analysis results and clinical findings of 27,504 patients from 35 universities and institutions in Turkey and Northern Cyprus are combined in an effort to provide a better insight into the genotype-phenotype correlation and how a specific variant contributes to certain clinical findings in FMF patients. Our results may help better understand this complex disease and how the genotype may sometimes contribute to phenotype. Unlike many studies in the literature, our study investigated a broader symptomatic spectrum and the relationship between the genotype and phenotype data. In this sense, we aimed to guide all clinicians and academicians who work in this field to better establish a comprehensive data set for the patients. One of the biggest messages of our study is that lack of uniformity in some clinical and demographic data of participants may become an obstacle in approaching FMF patients and understanding this complex disease