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Allogeneic stem cell transplantation (SCT) offers a potential cure for some hematological malignancies. For those patients without a family donor, unrelated donor (MUD) registries serve for identifying the best donor. In the present study, we aimed to give a cross-sectional report of our registry's activity and experience as the first established national MUD registry in the country. The study is retrospective and covers the period of 2016 to 2019. A total of 1855 donor searches were performed, and 642 were included in the study. All data were electronically obtained from the institutional database system. All SCTs were either 10/10 or 9/10 HLA matched and originated from an international registry. The most preferred stem cell source was peripheral blood (70.2%). A quarter of transplants were performed using bone marrow, and cord blood was used with a rate of 1.4%. The pandemic-related problems were similar for the other two national registries. During the pandemic, 71 of 432 patients who were searched for donors underwent stem cell transplant(SCT). The low number was related mostly with postponing of SCTs and/also difficulties in continuing of volunteering and in achievement of stem cells from international registry. During the Covid19 pandemic, the SCT activity of centers decreased according to the national, and international guidelines. The study revealed an organized, and multidirectional capacity of the registry and also the adaptation to unpredicted conditions such as pandemic. On the other hand, there is a need for more effective strategies for donor recruitment and retention programme.

In this work, an InGaN/GaN multiple quantum well based Top-Hat Hot-Electron Light Emission and Lasing in a Semiconductor Heterostructure (Top-Hat HELLISH) is investigated. A heterojunction structure is designed based on an active InGaN quantum well placed in the n-type GaN region sandwiched by the n-and p-type GaN layers. The four quantum well structure of an InGaN/GaN heterojunction where the Indium ratio is 0.16 has been grown via Metal-Organic Chemical Vapor Deposition. In order to create an anisotropic potential distribution of the heterojunction, it is aimed to fabricate TH-HELLISH-GaN device in Top-Hat HELLISH (THH) geometry for four contacts with separate n-and p-channels. High-speed I-V measurements of the device reveal an Ohmic characteristic at both polarities of the applied voltage. Integrated EL measurements reveal the threshold of the applied electric field at around 0.25 kV/cm. The emission wavelength of the device is around 440 +/- 1 nm at room temperature. (c) 2021 Elsevier B.V. All rights reserved.

Objective: HLA class I and II alleles are shown to be associated with certain diseases. A restricted numbers of alleles were found to be related to alloimmunisation in thalassemia population. The role of human leucocyte antigens in thalassemia is trend topic. In this study, the aim was to evaluate the differences in HLA frequencies of beta thalassemia patients comparing with healthy controls. Methodology: The data were collected of 100 patients who were diagnosed with beta thalassemia and 100 healthy controls were included in the study. The low resolution HLA-A, -B, -DRB1, tissue group data were performed Istanbul University, Faculty of Medicine, Medical Biology Department HLA typing laboratory. All data were analyzed retrospectively and their HLA allele frequencies were analyzed by SPSS (v22) program. Results: We found an increased frequency of HLA-B*14 (8% versus 2%) and HLA-B*52 (17% versus 2%) compared to the control group (p=0.05, OR=4.26; p

Background: The electrical and optical properties of nanoparticle-based devices depend on the shape, dimension and uniformity of these particles. Methods: In this work, we fabricated ordered Au nanodots using electron beam lithography and thermal evaporation. Au nanodot diameter and circularity varied with a changed exposure dose and resist thickness. Electron beam dose ranged from 5 fC to 200 fC for single dot patterns. Commonly used PMMA thin films of thicknesses 60 nm and 100 nm coated samples were used for investigating the resist thickness dependency with varying dose exposure. Results: The analyses of patterns show that the diameter and circularity of the Au nanodots ranged from smaller to larger diameters and from lower to higher circularities with increasing dose and resist thickness. Conclusion: The distributions of the nanodot diameter began to show Gaussian behavior at larger electron doses. Besides, single circularity value became dominant up to the medium doses and then a homogeneous distribution was observed with the increasing dose.

Objectives To investigate the association between mannose-binding lectin 2 (MBL2) codon 54 polymorphism and clinical features of patients diagnosed with schizophrenia (SCZ) or bipolar disorder (BD). Methods One hundred and eighteen patients with SCZ, 100 patients with BD, and 100 healthy volunteers were included in the case-control study. The patients consecutively admitted to the outpatient clinic in December 2017-May 2018 and were evaluated with some scales for clinical parameters. Polymerase chain reaction and RFLP were used to determine MBL2 polymorphism in DNA material. Results The MBL2 gene polymorphism distributions in SCZ or BD patients were significantly different from the control group. The heterozygous genotype percentages were significantly higher in the control group than in the SCZ or BD patients (OR: 0.450; 95% Cl: 0.243-0.830; p=0.010; OR: 0.532; 95%Cl: 0.284-0.995; p=0.047, respectively), and there were statistically significant differences in the MBL2 polymorphism distributions between treatment-responsive SCZ or BD patients and treatment-resistant patients diagnosed with SCZ or BD. The heterozygous genotype percentages were also significantly higher in the treatment-responsive group than in the treatment-resistant group in SCZ or BD patients (OR: 7.857; 95% Cl: 1.006-61.363; p=0.023; OR: 8.782; 95% Cl: 1.114-69.197; p=0.016, respectively). Conclusion The presence of a heterozygous MBL2 genotype seems to be favorable both in terms of the absence of SCZ and BD in the healthy population and treatment response for Turkish patients.

Electronic transport properties of as-grown and thermally annealed n- and p-type modulation-doped GaAsBi/AlGaAs quantum well (QW) structures were investigated. Hall mobility of as-grown, n- and p-type modulation doped QW structures are found from raw experimental data as ∼1414 and 95 cm2 Vs−1 at room temperature. A comparison between reported two-dimensional (2D) electron density determined from the analyses of Shubnikov de Haas oscillations and the 2D Hall electron density indicates a presence of parallel conduction in barrier layer (AlGaAs) and QW layer (GaAsBi) in n-type samples, therefore a parallel channel conduction theory is used to separate the electron mobility in the QW and the barrier layers in n-type modulation doped GaAsBi/AlGaAs QW structure. The extracted electron mobility of the as-grown n-type GaAsBi/AlGaAs QW sample is determined as ∼5975 cm2 Vs−1 at 4.2 K, which is closer to the electron mobility in GaAs. It is found that thermal annealing at lower temperature than growth temperature increases electron mobility of 2D electron gas, while annealing at higher temperature than growth temperature decreases electron mobility. The temperature dependence of the extracted electron mobility using parallel conduction approximation is analytically calculated by considering possible scattering mechanisms. Analysis of temperature-dependent electron mobility shows that the dominant scattering mechanisms are interface roughness (IFR), acoustic, and alloy-potential scatterings at low and intermediate temperature range, and IFR and optical phonon scattering at the high-temperature range in n-type modulation doped GaAsBi/AlGaAs QW structures. acceptedVersion

The operation of electronic devices is based on transport of electrons and holes within the solid from which the device is fabricated. It should be emphasised that for the carriers to accelerate between the contacts of the electronic device and to make a contribution to the current flow, they should be delocalised (free). Localised carriers cannot contribute to the conductivity. However, localised carriers are important in determining the dielectric properties of solids, thus the operation bandwidths, wavelength and polarisation characteristics of electronic and optoelectronic devices. In semiconductor devices such as diodes, transistors, photodetectors, photodiodes and lasers, both electrons and holes play an equally important role in device operation. The motion of free carriers under the influence of an external field is described with drift conductivity and motion resulting from an inhomogeneous distribution of free carriers is described with diffusion conductivity. In this chapter we aim to study in detail these two types of conductivity mechanisms.

Diodes are the backbone of today’s electronic and optoelectronics technology with a wide range of applications in amplifier circuits, digital electronics, solar cells, photodetectors, light emitting diodes and semiconductor lasers. A diode is a two terminal semiconductor device. The ideal diode would be a device exhibiting perfect rectifying action. To clarify, it would conduct in the forward direction without any potential drop across its terminals, while completely blocking conduction in the reverse direction. Optoelectronics devices are basically based on p-n junction diodes. In this chapter, we will introduce the fundamentals of a p-n junction diode.

An anisotropic etching of 1 eV Ga0.92In0.08N0.03As0.97 grown on (100) p-type GaAs substrate was investigated. Effects of the V-groove etching profile and metallization on the photovoltaic performance of the GaInNAs nipi solar cell with five periods are presented. Experimental results were supported by simulation studies considering the metal–semiconductor junction characteristics in the electrodes of nipi photovoltaic device. Standard wet etching processes at room temperature is applied using sulfuric acid based H2SO4: H2O2: H2O [1:8:8] solution to form the V-groove shape on the nipi sample. The etching characteristics in the [100] and $$\left\langle {011} \right\rangle$$ crystal directions are determined by using an interdigitated square spiral photolithographic mask. The scanning electron microscope (SEM) is used to analyze the V-groove etch profile. Two type of V-grooves achieved, one of them is in the $$\left[ {1\bar{1}1} \right]$$ direction and suitable to form metal electrodes for nipi layers and the second one is in $$\left[ {\bar{1}11} \right]$$ direction can be called a dovetail groove and not suitable for metal coating. Experimentally, the improvements observed in the short circuit current, open circuit voltage, and efficiency of the device despite some metallization failures. The effect of the metallization quality on the response to the spectrum can be clearly seen from the photovoltage spectrum. Essentially, these experimental results show that GaInNAs nipi devices have the potential to become high efficiency solar cells. Moreover, it can be possible to achieve high performance by integrating nipi devices into multijunction solar cells.

The optoelectronic device operation is fundamentally based on the interaction between photons and electrons. The aim of this chapter is to consider how electrical energy is converted into optical radiation using Light Emitting Diodes (LEDs) and Light Amplification by Stimulated Emission of Radiation (laser) devices. LEDs and lasers are widely used in current technologies and have applications in lighting, optical data processing, optical communications, medicine and spectroscopy. They emit light at wavelengths corresponding to the bandgap energies of the semiconductor materials from which they were fabricated. Therefore, the range of wavelengths they emit varies between UV for the wide bandgap semiconductors and IR for narrow bandgap semiconductors.

The sun releases a vast amount of energy into the solar system. The temperature at the surface of the sun is approximately 5800 K. At a point just outside the earth’s atmosphere the solar flux is about 1353 W/m2. Almost all renewable energy sources with exception to radiative and nuclear energy sources, have their energy from the sun. Solar cells (or photovoltaic cells) convert the energy from the sun light directly into electrical energy. In the production of solar cells both organic and inorganic semiconductors are used and the principle of the operation of a solar cell is based on the current generation in an unbiased p-n junction. In this chapter, an in-depth analysis of photovoltaic cells used for power generation is presented.

Pure (intrinsic) semiconductor materials have an extremely limited range of applications in the fabrication of semiconductor devices. The reason for the development of solid-state electronics based on semiconductor materials since the late 1950’s is that the conductivity of semiconductors can be tuned with introducing small quantities of selected impurity atoms into pure semiconductors in a highly controlled methods. This precisely controlled introduction of a range of useful impurity atoms into a pure semiconductor is referred to as doping of an intrinsic semiconductor to have a doped or extrinsic semiconductor. The significance of being able to dope semiconductors in this way lies in the fact that extremely small dopant density of the appropriate elements are capable of producing relatively large, but controlled changes in the electrical conductivity of semiconductor materials. A potentially infinite range of selectively doped extrinsic semiconductors forms the material basis of all semiconductor devices. The electrical conductivity of a material is determined by two material parameters, namely free charge carrier density in the material and their respective mobilities. To understand the physical basis of semiconductor device operation, it is necessary to acquire knowledge on how free carrier density changes by the addition of dopant atoms to semiconductor materials.

Solids are basically classified as being a metal (conductor), a semiconductor and an insulator. All these three type of solids are utilized in different areas in device technology. Metals interconnect devices and metallic bonds are necessary to measure or apply electric signals. Insulators are necessary to insulate devices from each other and they also form oxide layer in devices such as Metal Oxide Semiconductor Field Effect Transistor (MOSFET), Light Emitting Diode (LED), etc. In order to understand operation of optoelectronics devices, it is important to have knowledge about electrical and optical properties of semiconductors. In this chapter, we classify solids as metals, semiconductors and insulators according to their bandstructure and electrical properties and reveal that why their electrical properties are different from each other and why semiconductors are superior to metals and insulators. In order to understand operation of optoelectronics devices, it is important to have knowledge about electrical and optical properties of semiconductors. In this chapter, we classify solids as metals, semiconductors and insulators according to their bandstructure and electrical properties and reveal that why their electrical properties are different from each other and why semiconductors are superior to metals and insulators.

Amac: Hematolojik malign ve malign olmayan hastaliklarin tedavisinde hematopoietik kok hucre transplantasyonu (HKHT) icin ozellikle cocuk hastalarda kordon kani kok hucreleri uygulanmaktadir. Calismamizda Istanbul Tip Fakultesi Kemik Iligi Bankasi araciligi ile kordon kani transplantasyonu uygulanan alici ve vericilerin HLA uyumu ve hastalarin sag kalim acisindan retrospektif analizlerinin degerlendirilmesi amaclanmistir. Gerec ve Yontem: Bu calismada 2008 ve 2014 yillari arasinda gobek kordon kani hematopoietik kok hucre kaynagi kullanilarak transplantasyonu gerceklestirilen 102 vaka, retrospektif olarak analiz edilmistir. Kordon kani tarama basvurulari Istanbul Universitesi, Istanbul Tip Fakultesi, Kemik Iligi Bankasi araciligi ile gerceklestirilmistir. Bulgular: Kordon kani taramasindan transplantasyon islemine kadar gecen sure ortalama 45 gun (11-113 gun) olmustur. Hastalarin ortalama yaslari 42,48±2,8 ay (1-192 ay), erkek-kadin orani 64/38'dir. Bu grup icindeki vakalarin tanilari SCID (n=23), AML (n=13), osteopetroz (n=10), ALL (n=10) ve diger hastaliklardir (n=46). Kordon kani transplantasyonu gerceklestirilen 102 vakadan (%53), HLA-A veya -B antijen uyumsuzlugu; 9 vakada (%9) HLA-DR uyumsuzlugu, 1 vakada (%1) HLA-B veya -DR antijen uyumsuzlugu varken 38 vakada (%37) HLA -A, -B, -DR lokuslari tam uyumlu idi. HKHT'den sonra kordon kani ile tam uyumlu hastalarin genel sag kalim orani %81,5 (n=31/38) iken Sinif-I HLA antijen uyumsuzlugu olan hastalarin genel sag kalim orani %48,1 (26/54), Sinif-II HLA antijen uyumsuzlugu olan hastalarinki ise %22,2 (2/9) idi. Sonuc: Calismamizda 6/6 HLA uyumlu kordon kanindan gerceklestirilen transplantasyonlarin hastalarin genel sag kalimi uzerinde onemli etkisi oldugu tespit edilmistir. Bu baglamda, ozel kordon bankalari disinda, akraba disi kordon kani transplantasyonlari icin resmi kordon kani bankalari kurulmasi suretiyle Turkiye'deki kordon kani transplantasyonu sayisi arttirilabilir.

We present optical identification of deep level defects in as-grown and annealed GaBixAs1−x(x=0, 0.013 and 0.015) alloys grown at different temperatures (220 °C and 320 °C) by using photo-modulated reflectance (PR) spectroscopy and photoluminescence (PL). The PR measurements are employed at above- and below-bandgap excitations, and the PR line-shape is analyzed by the third derivative functional form (TDFF). The PR at below-bandgap excitation reveals transitions at 0.757 ±0.001 eV and 0.710 ±0.002 eV at 30K and 300K, respectively. Franz-Keldysh oscillations are observed in all samples under above-bandgap excitation at PR measurements, and the built-in electric field, which may originate from the charged As-antisite defects is calculated from local extrema points in the PR spectra. The decrease in the built-in electric field after thermal annealing is explained with decreased point defect density.

OBJECTIVES This study aimed to analyze and compare the topographical, chemical, and osseointegration characteristics of a sandblasted acid-etched surface (SLA group), a sandblasted thermally oxidized surface (SO group), and a surface chemically modified by hydrofluoric (HF) acid (SOF group). MATERIALS AND METHODS Following the preparation and characterization of the relevant surfaces, 90 implants (30 for each group) were placed on the pelvic bone of six sheep. Resonance frequency analysis (RFA), insertion (ITV), removal torque value (RTV), and histomorphometric analyses (BIC%) were performed after three and 8 weeks of healing. The results were analyzed by nonparametric tests (p

The temporal response characteristics of a GaInNAs-based vertical resonant cavity enhanced photodetector device are presented for operation at λ ≈ 1.3 μm. The absorption layers of the device are composed of nine 7-nm-thick Ga0.65In0.35N0.02As0.98 quantum wells and are sandwiched between top and bottom AlGaAs/GaAs distributed Bragg reflectors (DBRs). The temperature dependence of the transient photoconductivity (TPC) under different light intensities and bias voltages is reported. Photoluminescence measurements were also performed on structures with and without the top DBR to determine their optical response under continuous illumination. The response time was measured using excitation from a 1047-nm pulsed neodymium-doped yttrium lithium fluoride laser with pulse width of 500 ps and repetition rate of 1 kHz. The rise time of the TPC was 2.27 ns at T = 50 K, decreasing to 1.79 ns at T = 300 K. The TPC decay time was 25.44 ns at T = 50 K, decreasing to 16.58 ns at T = 300 K. With detectivity of $$ 2.28 \times 10^{10} \,{\hbox{cm}}\sqrt {\hbox{Hz}} / {\hbox{W}} $$ and noise-equivalent power of $$ 2.45 \times 10^{ - 11} \,{\hbox{W/}}\sqrt {\hbox{Hz}} $$ , the proposed device is faster and more sensitive with better signal-to-noise ratio compared with other GaInNAs-based resonant cavity enhanced photodetectors (RCEPDs) for operation at 1.3 μm.

We report the characteristics of the temperature dependent operation of a GaInNAs-based resonant-cavity-enhanced photodetector (RCEPD), designed to be operated at the dispersion minimum optical communication window of 1.3 μm. A Transfer-Matrix Method (TMM) was used to design the structure of the device. The absorption layer of the photodetector is comprised of nine 7 nm-thick Ga 0.733 In 0.267 N 0.025 As 0.975 (Sb)/ GaN 0.035 As 0.965 quantum wells, and 15 and 10 pairs of GaAs/AlAs distributed Bragg reflectors (DBRs) grown as the bottom and top mirrors, to form the cavity of the device. All electrical and optical measurements were carried out over a temperature range from 10 to 40 °C in order to investigate the characteristic of the device. The quantum efficiency is determined to be in the range of 16% (at 10 °C) and 31% (at 40 °C). An excellent wavelength selectivity is observed which changed from 3.7 nm (at 10 °C) to 5.4 nm (at 40 °C). The dark current of the device is measured as 11 nA at 10 °C and 19 nA at 40 °C without bias. The photocurrent at −0.5 V is measured to be 1.5 mA at 25 °C. The high dark current of the device is attributed to weak confinement of the electrons in GaInNAs QW surrounded by the strain-compensator GaNAs barrier layers. The temperature dependent cavity wavelength was analytically calculated and compared with that of experimental results. The temperature dependent linear shifts of the resonance wavelength ( d λ / d T ) is calculated as 0.077 nm/°C, which is in good agreement with the experimental result, 0.080 nm/°C. Our results reveal that the characteristics of a RCEPD, such as quantum efficiency, FWHM etc., are quite sensitive to temperature changes due to the temperature dependence of the refractive index of the DBRs.

Herein, a new heterostructured ultraviolet metal–semiconductor–metal photodetector based on Mg0.67Ni0.33O thin film and SrTiO3 is reported. The metal–semiconductor–metal photodetector comprises a 22 nm epilayer of Mg0.67Ni0.33O grown on SrTiO3 (111) substrate by molecular beam epitaxy. A comparison of responsivities of the Mg0.67Ni0.33O–SrTiO3 photodetector and reference SrTiO3 photodetector shows that the heterostructured detector has close to an order of magnitude enhanced responsivity in the deep-ultraviolet region. The responsivity of the Mg0.67Ni0.33–SrTiO3-based photodetector at 320 nm is 415 mA W−1, with dark current lower than 40 pA at a bias of 10 V. The rise and fall times of Mg0.67Ni0.33O–SrTiO3 photodetector are 10.7 and 8.6 ms, respectively, with the rise time more than two orders of magnitude shorter than the reference SrTiO3 photodetector.

A non-volatile floating gate memory device containing well-ordered Au nanoparticles (NPs) is fabricated as a metal-oxide-semiconductor capacitor structure. With superior control on the size, shape and position of nanoparticles, the presented nano-floating gate memory (NFGM) device possesses almost perfect precision of device geometry. The well-ordered Au NPs embedded within the memory device exhibit large memory window at low operation voltages (8.8V @ ± 15V), fast operation time (

Resonant cavity LEDs (RCLEDs) are a viable and low-cost alternative light source to lasers for optical communication systems in the 1.3 µm O-band. Most work in this area has been conducted on InP-based material, which is inherently costly, devices often require cooling and the refractive index contrast for constructing mirrors is low. Here, we demonstrate a high-performance GaAs-based RCLED using a dilute nitride GaInNAs active layer emitting in the 1.3 μm wavelength window. While previous 1.3 µm RCLEDs have used metallic mirrors on the back of the device, we exploit the high refractive index contrast of the GaAs/AlAs system to place Distributed Bragg mirrors on both sides of the active layer and achieve superior performance. The external quantum efficiency of the devices is 20% and the full width at half maximum of the emission spectrum is 5.2 nm at room temperature, into a narrow angular cone. The emission power from an 88 μm diameter aperture is 0.5 mW, which, together with the narrow spectral linewidth, makes the device suitable for deployment in a coarse Wavelength Division Multiplexing (WDM) communications system.

Simulated and experimental properties of a Ga(1-x)In(x)As(1-y)N(y)nipi solar cell involving V-grooves for contact formation are reported. In particular, using a drift-diffusion model, we simulate the conversion efficiency, the short-circuit current density (J(SC)), and the open-circuit voltage (V-OC) as a function of the number of nipi junctions. Based on the modelling results, optimized nipi solar cell incorporating five n-p junction pairs was grown on a p-type GaAs (100) substrate using molecular beam epitaxy (MBE). The bandgap of the nipi structure was determined to be 1eV. The metal contacts of the nipi solar cell structure were processed in the form of mesa and V-groove. These shapes enable both vertical and horizontal carrier transport within the solar cell. The effect of thermal annealing on J-V characteristics of both type of devices is finally assessed. The results point out that the V-groove sample has better photovoltaic characteristics than the mesa structure sample.

We report on a novel dilute nitride-based resonant cavity enhanced photodetector (RCEPD) operating at 1.286 μm. The RCEPD was fabricated using 21 pairs top and 24 pairs bottom GaAs/AlGaAs distributed Bragg reflectors for mirrors and 7 nm thick nine GaAs/Ga 0.65 In 0.35 N 0.02 As 0.98 quantum wells as the absorption region. For a 15 μm diameter window, the photocurrent at 1.286 μm is 27 μA and 42 μA, at V = 0 and −1 V, respectively, whereas the dark current is as low as 1.7 nA at −1 V. At the operating wavelength, an excellent wavelength selectivity with a full width at half maximum (FWHM) of 5 nm, and a high quantum efficiency of 43% are demonstrated. The device exhibits significant internal gain at very small reverse bias voltages of V ⩾ −2 V with an overall quantum efficiency of 67%. These are the best ever recorded values for a dilute nitride RCEPD.

9th Nanoscience and Nanotechnology Conference (NANOTR) -- JUN 24-28, 2013 -- Erzurum, TURKEY, WOS: 000344380500018, In this work, observed zero-bias offsets in I-V characteristics and differences in J-V characteristics of staircase quantum well infrared photodetectors were investigated. Temperature and voltage sweep rate dependence of the zero-bias offsets were studied on mesa structures shaped in different diameters. Furthermore, effect of mesa diameter on J-V characteristics was investigated. The temperature, initial bias voltage and voltage sweep rate dependence of the zero-bias offsets were explained by a qualitative model, which is based on a RC equivalent circuit of the quantum well infrared photodetector, Scientific and Technological Research Council of Turkey (TUBITAK) [108T721]; COST Action [MP0805]; Scientific Research Projects Coordination Unit of Istanbul University [3587], This study was partially supported by The Scientific and Technological Research Council of Turkey (TUBITAK) Project Number 108T721, partially supported by COST Action MP0805, partially supported by Scientific Research Projects Coordination Unit of Istanbul University, Project Number 3587. We are also grateful to University of Sheffield for growing the QWIP structure.

The structural and photovoltaic properties of the GaAs/GaAsBi pin solar cell with GaAs0.983Bi0.017 active layer are investigated by optical and electrical measurement techniques. The bandgap of GaAsBi active layer is determined to be 1.3 eV at room temperature. Current density-voltage (J-V) under AM 1.5G spectrum and spectral response measurements are carried out to determine photovoltaic properties of the solar cell. The presence of a midgap trap levels in GaAsBi active layer is identified by deep level transient spectroscopy (DLTS). J-V characteristics is analysed by using Sah-Noyce-Shockley (SNS) theory which includes the midgap trap found in DLTS measurement. The observed deviation between experimental and calculated J-V results is ascribed for metallic cluster formation at the interface between GaAs emitter and GaAsBi intrinsic active layer. Interface metallic clusters create local Schottky junction between emitter and active layers. The best fit to the experimental J-V characteristic of the solar cell is obtained by considering the presence of GaBi metallic cluster at the interface between GaAs emitter and GaAsBi active layer of the solar cell. We showed that work function of interface clusters have a significant effect on the open circuit voltage and filling factor.

In this work electronic hand structure of dilute bismide GaAs/GaAs1-xBix quantum well structures with 1.8% and 3.75% bismuth compositions have been investigated both experimentally and theoretically. Photoluminescence (PL) measurements reveal that effective bandgap of the samples decreases approximately 65 meV per bismuth concentration. Temperature dependence of the effective bandgap is obtained to be higher for the sample with higher bismuth concentration. Moreover, both asymmetric characteristic at the low energy tail of the PL, and full width at half maximum (FWHM) of PL, peak increase with increasing bismuth composition as a result of increased Bi related defects located above valence band (VB). In order to explain composition dependence of the effective bandgap quantitatively, valence hand anti-crossing (VBAC) model is used. Bismuth composition and temperature dependence of effective bandgap in a quantum well structure is modeled by solving Schrodinger equation and compared with experimental PL data.

DAG (Eastern Anatolia Observatory in Turkish) will be the newest and largest (4m) observatory of Turkey in both optical (VIS) and near-infrared (NIR) Owith its robust observing site infrastructure. The telescope is designedOto house 2 Nasmyth platformes which will be dedicated to NIR and VIS observations. A collaboration has recently been established among four Turkish universities including FMV Isik University (for adaptive optics systems), Middle East Technical University (fort measurement, test and calibration purposes), Istanbul University (for new technology instruments, e.g. MKIDs) and as the coordinator Ataturk University (for obtaining NIR and VIS instruments). In this paper the status of the recently approved FPI project and its aims are presented and possible collaboration opportunities are emphasized. Publisher's Version

As-grown and annealed Ga0.6In0.4N0.005As0.995/GaAs with 1, 3, and 7 quantum well structures grown by Molecular Beam Epitaxy (MBE) are investigated using Photoluminescence (PL) and Photo-Induced Current Transient Spectroscopy (PICTS) measurements in order to determine the effects of the number of quantum wells and thermal annealing on optical properties and qualities of the structures. PICTS results reveal that all the samples with different quantum well numbers have two dominate trap levels which related to GaInNAs layer. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

An investigation is presented of thermal annealing effects on spectral photoconductivity and photoluminescence in sequentially grown GaInNAs/GaAs and GaInAs/GaAs quantum well structures. Experiments have been carried out at temperatures between 30 K and 300 K. The results indicate that thermal annealing improves the optical quality of GaInNAs, but may cause either a blue shift, as commonly observed by other groups, or a red shift depending on the growth technique. The anneal-induced blue-shift behaviour can be explained in terms of two competing mechanisms involving the redistribution of nearest-neighbour configuration and the change of quantum well profile. The red shift is explained in terms of hydrogen-induced chemical effects.

An investigation of the Photoconductivity (PC) and Inplane Photovoltage (IPV) response of an undoped GaInNAs quantum well (QW) was carried out in the transient and steadystate modes using the 1.064µm line of a Nd:YAG laser as the excitation source. In this paper we focus on the behaviour of the nonlinear response of the transient PC (TPC) signal to excitation intensity. All PC measurements were performed at room temperature. Temperature and excitation intensity were considered instead in the study of the IPV signal.

The operation of the hot electron light emitting and lasing in semiconductor heterostructure – vertical cavity surface emitting laser (HELLISH–VCSEL) devices is based on hot carrier transport parallel to the layers of Ga1-x Alx As p–n junction. It is therefore a field-effect device and the light emission from the device is independent of the polarity of the applied voltage. The authors present a study of the temperature dependence of the operational characteristics of the device. Experimental studies comprise the measurements of the I–V characteristics, electroluminescence, reflectivity, and temperature-dependent light-applied electric field (L–F) characteristics. To obtain the optimum operation temperature, the gain calculations, reflectivity spectra, and band gap calculations were carried out at different temperatures. The temperature dependence of the threshold electric field is compared with the model calculations, where radiative transitions without momentum (k) selection are considered.

We report the results of our studies of optical and electro-optic properties of GaInNAs/GaAs single quantum wells grown by chemical beam epitaxy. The quantum wells have been characterised by scanning transmission electron microscopy and energy dispersive X-ray analysis. Photoluminescence measurements from sequentially grown GaInAs and GaInNAs quantum wells were carried out between 4 K and room temperature. A significant difference in the temperature dependence of GaInNAs band gap compared to nitrogen-free GaInAs is observed. Photoluminescence results are used to determine the interband transition energies. The results are compared with the theoretical values obtained using the band-anticrossing model. When the device is illuminated with monochromatic light, a finite photovoltage develops in the plane of the quantum wells due to Fermi level fluctuations.

We present electronic transport in n- and p-type modulation-doped GaInNAs/GaAs quantum well structures. The Hall mobility of electrons in the n-type material decreases dramatically with increasing nitrogen composition. The mobility of 2D holes in p-modulation-doped quantum wells is significantly higher than that of 2D electrons in n-modulation-doped material with similar nitrogen concentration. The mobility of 2D electrons is discussed using a S-matrix model for N-related alloy scattering. The results indicate that the electron mobility is intrinsically limited by scattering from nitrogen complexes. The high mobility of 2D holes is explained in terms of negligible effect of nitrogen on valance band and the absence of scattering with localized nitrogen complexes.

WOS: 000313393300034, The effect of indium and nitrogen mole concentrations on the nonlinear optical properties in a Ga1-xInxNyAs1-y/GaAs single quantum well under the intense laser field is theoretically studied within the effective mass approximation and the envelope function approach. The analytical expressions of optical properties are obtained by using the compact density-matrix approach. The numerical results show that the linear, third-order nonlinear and total absorption and refractive index changes depend both on the intense laser field and on the indium and nitrogen concentrations. From the findings of this study, it has been concluded that the linear and nonlinear optical properties in a Ga1-xInxNyAs1-y/GaAs single quantum well under the intense laser field can be tuned by changing the indium and nitrogen mole fraction. (c) 2012 Elsevier B.V. All rights reserved., Scientific and Technological Research Council of Turkey (TUBITAK) [COST 109T650]; Scientific Research Project Fund of Cumhuriyet University [F-360], This research was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) for a research Grant COST 109T650 and also was partially supported by Scientific Research Project Fund of Cumhuriyet University under the project number F-360.

WOS: 000315516800001, PubMed ID: 23146126, In this study, photomodulated reflectance (PR) technique was employed on two different quantum well infrared photodetector (QWIP) structures, which consist of n-doped GaAs quantum wells (QWs) between undoped Al (x) Ga1-x As barriers with three different x compositions. Therefore, the barrier profile is in the form of a staircase-like barrier. The main difference between the two structures is the doping profile and the doping concentration of the QWs. PR spectra were taken at room temperature using a He-Ne laser as a modulation source and a broadband tungsten halogen lamp as a probe light. The PR spectra were analyzed using Aspnes' third derivative functional form. Since the barriers are staircase-like, the structure has different ground state energies; therefore, several optical transitions take place in the spectrum which cannot be resolved in a conventional photoluminescence technique at room temperature. To analyze the experimental results, all energy levels in the conduction and in the valance band were calculated using transfer matrix technique, taking into account the effective mass and the parabolic band approximations. A comparison of the PR results with the calculated optical transition energies showed an excellent agreement. Several optical transition energies of the QWIP structures were resolved from PR measurements. It is concluded that PR spectroscopy is a very useful experimental tool to characterize complicated structures with a high accuracy at room temperature., Scientific and Technological Research Council of Turkey (TUBITAK) [108T721]; COST Action [MP0805]; Scientific Research Projects Coordination Unit of Istanbul University [3587, UDP 16607]; Ministry of Development of Turkey [2010K121050], We are grateful to Dr. Bulent Aslan and Dr. Ugur Serincan from Anadolu University for growing the ANA samples with MBE. This work was partially supported by The Scientific and Technological Research Council of Turkey (TUBITAK; project number 108T721), COST Action MP0805, Scientific Research Projects Coordination Unit of Istanbul University (project numbers 3587 and UDP 16607), and the Ministry of Development of Turkey (project number 2010K121050).

3rd International Symposium on Growth of III-Nitrides (ISGN) -- JUL 04-07, 2010 -- Montpellier, FRANCE, WOS: 000301569300046, In this work, a quantum well infrared photodetector structure which consists of three different well thicknesses with three different barrier compositions producing a staircase-like conduction band profile with the reputation of 30 periods has been investigated. Dark current measurements have been done at the range from 6 K to 290 K temperature. Activation energies of the carriers have been obtained from the temperature dependence of the I-V measurements. The change of the activation energy with bias voltage has also been obtained. From the activation energy at zero bias and calculated quasi Fermi energy, barrier heights of the quantum wells and ground state energies were obtained. All obtained ground state energies have been found to be consistent with the results obtained from calculations with the transfer matrix method, Univ Montpellier, Natl Centre Sci Res, Inst Phys, Conseil Regional Languedoc Roussillon, Montpellier Agglomerat, AIXTRON, SAFC Hitech, Scientific and Technological Research Council of Turkey (TUBITAK) [108T721]; Cost Action [MP0805]; Scientific Research Projects Coordination Unit of Istanbul University [3587], This study was partially supported by The Scientific and Technological Research Council of Turkey (TUBITAK) Project Number 108T721, partially supported by Cost Action MP0805 and partially supported by Scientific Research Projects Coordination Unit of Istanbul University, Project Number 3587.

The operation of the Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure -- Vertical Cavity Surface Emitting Laser (HELLISH-VCSEL) devices is based on hot carrier transport parallel to the layers of Ga1-xAlxAs p-n junction. It is therefore a field - effect device and the light emission from the device is independent of the polarity of the applied voltage. In this study, we present the temperature dependence of the operational characteristics of the device. Experimental studies comprising of the measurements of the I-V characteristics, electroluminescence, reflectivity, and temperature dependent light-applied electric field (L-F) characteristics are conducted to find the optimum operating temperature of the device.

Teke, Ali (Balikesir Author), We have studied the optical quality of sequentially grown undoped Ga0.8In0.2As and Ga0.8In0.2N0.015As0.985 quantum wells (QWs). Spectral and time-resolved in-plane photovoltage (IPV) and photo-induced transient spectroscopy (PITS) techniques were used in this investigation. Two clear peaks have been observed and analysed in the PITS experiment. Spectral and transient IPV in the same samples has been investigated and a selective light was used as the excitation source to separate the GaInNAs IPV from the other layers. IPV can be explained in terms of random fluctuations of the Fermi level in undoped QWs. Spectral and time-resolved IPV measurements can therefore be used to obtain qualitative and quantitative information about interband transitions and trap activation energies.

The spectral dependence of in-plane photovoltage (PV) and photoconductivity (PC) in sequentially grown GaInAs and GaInNAs double quantum well (DQW) heterostructures has been investigated. The spectra were taken at different temperatures, ranging from 30 K to 300 K. Optical spectra obtained from PV and PC measurements were found to be complementary and are discussed in terms of possible optical transitions in the structure.

Photocurrent oscillations, observed at low temperatures in lattice-matched Ga1−x In x N y As1−y /GaAs multiple quantum well (MQW) p-i-n samples, are investigated as a function of applied bias and excitation wavelength and are modelled with the aid of semiconductor simulation software. The oscillations appear only at low temperatures and have the highest amplitude when the optical excitation energy is in resonance with the GaInNAs bandgap. They are explained in terms of electron accumulation and the formation of high-field domains in the GaInNAs QWs as a result of the disparity between the photoexcited electron and hole escape rates from the QWs. The application of the external bias results in the motion of the high-field domain towards the anode where the excess charge dissipates from the well adjacent to anode via tunnelling.