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Colorectal cancer is the most common tumor of the gastrointestinal system. The conventional treatment options of colorectal cancer are troublesome for both patients and clinicians. Recently, mesenchymal stem cells (MSCs) have been the novel focus for cell therapy due to its migration to tumor sites. In this study, the apoptotic effect of MSCs on colorectal cancer cell lines has been aimed. HCT-116 and HT-29 were selected as the colorectal cancer cell lines. Human umbilical cord blood and Wharton’s jelly were used as mesenchymal stem cell sources. To discriminate against the apoptotic effect of MSC on cancer, we also used peripheral blood mononuclear cells (PBMC) as a healthy control group. Cord blood-MSC and PBMC were obtained by ficoll-paque density gradient, and Wharton’s jelly-MSC by explant method. Transwell co-culture systems were used as cancer cells or PBMC/MSCs at ratios of 1/5 and 1/10, incubation times of 24 hours and 72 hours. The Annexin V/PI-FITC based apoptosis assay was performed by flow cytometry. Caspase-3 and HTRA2/Omi proteins were measured by ELISA. For both ratios in both cancer cells, it was found that the apoptotic effect of Wharton’s jelly-MSC was significantly higher in 72-hour incubations (p

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.

Focused ion beam (FIB) is an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate, atomically thin materials, especially in extended areas beyond the FIB target, has not yet been fully characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. The emission in these three zones have different wavelengths and decay lifetimes. An unexpected bright ring-shaped emission around the milled location has also been revealed by time-resolved PL spectroscopy with high spatial resolution. Our findings open up new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale.

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

Pure GaAs and GaAs1−xBix alloys with different Bi ratios (1 %, 2.5 %, 3.5 %) fitted with silver contacts were measured with a dielectric spectroscopy device. Dielectric characterization was performed at room temperature in the frequency range of 0.1 Hz to 1 MHz. GaAs exhibits three relaxation regions corresponding to space-charge, dipolar and ionic polarizations in sequence with increasing frequency while GaAs1−xBix samples show only a broad dipolar polarization in the same frequency range. This result proves the filling of the lattice with Bi through making a new bonding reducing the influence of ionic polarization. This finding supports the previous results concerning optical properties of GaAs1−xBix, presented in the literature.

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 band line-up and band offset calculations of GaAs0.978Bi0.022/GaAs single quantum well with spatial changes of Bi composition were reported. The spatial Bi profile and a certain amount of the Bi composition in the barrier layer were determined by HR-XRD measurements. Virtual Crystal Approximation and Valence Band Anti-Crossing models were used including strain effects to obtain conduction and valence band edge shifts with Bi incorporation. Photoluminescence (PL) measurements were performed at a low temperature of 8 K as a function of excitation intensity. The PL spectra have shown asymmetric line shapes, which were fitted with different Gaussian functions. Comparing experimental PL results with calculated band edge energies, it was found that optical transition is a type I under low intensity excitation while the optical transition is switched from type I to type II due to the spatial changes in Bi concentrations. The band offsets Δ E c / Δ E v were also determined.

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.

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.

In this work, optical properties of n- and p-type modulation doped GaAsBi/AlGaAs single quantum well (QW) heterostructures are investigated via temperature-and excitation power-dependent photoluminescence (PL) and integrated photoluminescence (IPL) studies and the results are compared to the nand p-type GaAs/AlGaAs QW structures to determine the influence of Bi and doping type on the optical properties. The results of the temperature dependent PL peak energy reveal that, as an effect of doping type, the temperature dependence of the PL peak energy exhibit different characteristic for n-and p-type samples. The temperature dependence of the PL peak energy reveals S-shaped trend for the n-type GaAsBi/AlGaAs QW sample. On the other hand, the characteristic follows Varshni law for the p-type GaAsBi/AlGaAs QW sample. The observed S-shaped behaviour for the n-type sample is explained by considering the contribution of the Bi-induced states above valence band (VB) to the PL. As for p-type sample, the localised states-related contribution to the PL signal is drastically diminished, resulting in an almost S-shape free temperature dependence of the optical transition energy, which can be explained by the compensation of acceptor-like states. The observed PL spectra of n-and p-type samples successfully reconstructed by two Gaussian peaks, which are assigned to optical transitions due to recombination of free and localised excitons. The localised exciton-related peak is observed to be very weak in p-type sample compared to that in n-type one. The allowed transitions in GaAsBi QW is calculated by selfconsistently solving the Schr_odinger-Poisson equation to identify the origin of the observed transitions. A comparison of the PL results of the Bi-containing samples with the results of the Bi-free ones is exhibited approximately 80 meV/Bi% decrease in the fundamental optical transition. Using the excitation-dependent IPL measurements, it is found that at low temperatures and under low excitations, recombination process is under the effect of Shockley-Read-Hall (SRH) non-radiative process. When the excitation power density increases, radiative recombination becomes dominant. At higher-temperatures and in the high-intensity regime, we observed Auger effect in recombination process for n-and p-type GaAsBi samples, but the effect of Auger loss is observed to be much less in the p-type GaAsBi sample due to enhanced spin orbit split-off energy as a result of incorporation of bismuth. Furthermore, when we compare the result for Bi-free and Bi-containing p-type samples, again, Auger recombination is found to be less effective for the Bi-containing sample. (C) 2017 Elsevier B.V. All rights reserved.

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 study structural properties and surface formation of undoped, n- and p-type doped GaAsBi alloys with various bismuth compositions using Micro-Raman, Fourier Transform (FT) Raman, Photoluminescence (PL) and Atomic Force Microscopy (AFM) techniques. PL is used to determine the suitable excitation source for Raman measurements and evaluate the Raman spectroscopy results. Room temperature PL results reveal that the bandgap energy of GaAsBi decreases with increasing bismuth composition at a rate of 82meV/%Bi. In micro-Raman spectra recorded using 532 nm laser line, a peak at around 185 cm(-1) and a broad peak located between 210 and 250 cm(-1) are observed. The absence of these peaks in the Raman spectrum of low temperature (LT) growth GaAs indicates that those peaks are bismuth-induced vibrations. Besides, the forbidden transverse optical (TO) mode (269 cm(-1)) becomes more pronounced for the samples as bismuth composition increases. FT-Raman spectra taken by 1064 nm laser line of the n- and p-type samples exhibit different characteristics; while TO and longitudinal optical (LO) peaks (291 cm(-1)) are present in n-type sample as sharp vibrational peaks, a broad peak located at slightly lower wavenumber than TO mode appears and LO peak is suppressed. The ionised acceptor and free hole system respond incident electromagnetic field as plasma oscillations. Moreover, the amplitude of the plasma oscillations enhances with higher doping density. Therefore, the appearance of the broad peak in FT-Raman spectrum of p-type GaAsBi is explained with an LO-plasmon coupling (LOPC). As for n-type samples, free electrons are compensated by free holes in GaAsBi that originate from Bi-induced acceptor-like defects. Therefore, we do not observe the effects of plasma oscillations in FT-Raman spectrum. AFM results reveal that all samples have surface droplets, and the size of the droplets is not affected from doping density or doping type, but bismuth composition. The surface droplets are removed by a chemical process to investigate the effect of the droplets on Raman spectrum. Our results reveal that removing surface droplets does not change the characteristic of Raman spectrum, but enhances the Raman intensity due to the reflected light by droplets decreases, leading to more photons penetrate and scattered from inside the sample. (C) 2017 Elsevier B.V. All rights reserved.

Effect of thermal annealing on quantum transport properties have been investigated on as-grown and annealed n-type modulation doped GaInNAs/GaAs quantum well (QW) structures with various nitrogen concentration in low (B

We report on the power loss mechanisms of hot electrons in as-grown and annealed n-type modulation-doped Al0.15Ga0.85As/GaAs1-xBix (x = 0 and 0.04) quantum well structures considering acoustic phonon interactions via the deformation potential (non-polar) and piezoelectric (polar) scatterings. The two-dimensional (2D) electron gas is heated by applying various electric fields under a steady-state magnetic field, and the effect of the applied electric field on the Shubnikov de Haas (SdH) oscillations is analyzed to investigate the power loss mechanism. The temperature of hot electrons (T e) has been obtained by comparing the lattice temperature and applied electric field dependencies of the SdH oscillation amplitude. The hot electron temperature is almost the same for both Bi-free and Bi-containing samples except for the sample annealed at a higher temperature (700 °C) than the growth temperature of GaAsBi. The electron temperature dependence of power loss is analyzed using current theoretical analytic models derived for 2D semiconductors. We find that energy relaxation occurs in the intermediate temperature regime, including mixing of piezoelectric and deformation potential scattering. The power loss of hot electrons is found to be proportional to (Teγ-TLγ) with γ in the range from 2.4 to 4.2, which indicates that the hot electron relaxation is due to acoustic phonon scatterings via unscreened deformation potential and piezoelectric scattering. It is found that deformation potential scattering is dominant over piezoelectric scattering in the Bi-free sample, while the incorporation of Bi into the GaAs lattice makes these processes comparable. After thermal annealing at lower than growth temperature (350 °C), the scattering mechanism switches from deformation potential to piezoelectric scattering. After thermal annealing at higher than growth temperature (700 °C), the theoretical model does not fit to the experimental results due to degradation of the sample. acceptedVersion

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.

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.

In this work, the electronic bandstructure of GaAs 1-x Bi x /GaAs single quantum well (QW) samples grown by molecular beam epitaxy is investigated by photomodulated reflectance (PR) measurements as a function of Bi content (0.0065 ? x ? 0.0215) and substrate orientation. The Bi composition is determined via simulation of high-resolution x-ray diffraction measurement and is found to be maximized in the 2.15%Bi and 2.1%Bi samples grown on (100) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi QW layer but extends out of the GaAsBi QW towards the GaAs barrier and forms a GaAsBi epilayer. PR spectra are fitted with the third derivative function form (TDFF) to identify the optical transition energies. We analyze the TDFF results by considering strain-induced modification on the conduction band (CB) and splitting of the valence band (VB) due to its interaction with the localized Bi level and VB interaction. The PR measurements confirm the existence of a GaAsBi epilayer via observed optical transitions that belong to GaAsBi layers with various Bi compositions. It is found that both Bi composition and substrate orientation have strong effects on the PR signal. Comparison between TDFF and calculated optical transition energies provides a bandgap reduction of 92 meV/%Bi and 36 meV/%Bi and an interaction strength of the isolated Bi atoms with host GaAs valence band (C BiM ) of 1.7 eV and 0.9 eV for (100) and (311)B GaAs substrates, respectively. © 2018 IOP Publishing Ltd. Fundação de Amparo à Pesquisa do Estado de São Paulo: 14/ 50513-7, 16/10668-7 Firat University Scientific Research Projects Management Unit: FYD-2016-20128, ONAP-52321 115F063 Academy of Finland: 259111 695116 European Research Council This work was partially supported by the Scientific Research Projects Coordination Unit of Istanbul University (ONAP-52321 and FYD-2016-20128) and supported by The Scientific and Technical Research Council of Turkey (TUBITAK) under Grant No. 115F063. YGG acknowledges the financial support from FAPESP ( grants numbers 16/10668-7 and 14/ 50513-7). JP, JH and MC acknowledge the financial support from European Research Council (ERC AdG AMETIST, #695116) and the Academy of Finland (TransPhoton, #259111).

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.

We investigate electronic transport properties of as-grown and annealed n-type modulation-doped Al0.15Ga0.85As/GaAs1-xBix (x = 0 and 0.04) quantum well (QW) structures using magnetotransport measurements in the temperature range 4.2 K and 60 K and at magnetic fields up to 18 T. Thermal annealing process was applied at two different temperatures, 700 degrees C and 350 degrees C during 60 s and 180 s, respectively. We find that electron effective mass and 2D electron density in as-grown Bi-containing sample are slightly lower than that in Bi-free one. Furthermore, quantum electron mobility and quantum scattering time are observed to be decreased in Bi-containing samples. The annealing process at 700 degrees C causes a slight increase in electron effective mass and 2D electron density. A negligible decrease in electron effective mass and an increase in 2D electron density are determined following annealing at 350 degrees C. The observed change in electron effective mass following thermal annealing process is attributed to changing 2D electron density in the samples. No improvement on quantum electron mobility and quantum scattering time are observed following thermal annealing at both process temperatures. We determine that one electron subband (e1) for as-grown and annealed (at 700 degrees C for 60 s) Bi-containing QWs and two electron subbands (e1 and e2) for the annealed (at 350 degrees C for 180 s) GaAsBi QW sample and the Bi-free QW sample contribute to electronic transport. Our results reveal that there is no significant direct effect of Bi on effective electron mass, but an indirect effect, in which Bi can provoke changes in 2D electron density and hence causes not to observe actual band-edge electron mass but a deviation from its band-edge value. Therefore, it can be concluded that dispersion curve of conduction band does not change as an effect of Bi incorporation in GaAs.

In this work, magnetoresistance of as-grown and annealed n- and p-type modulation-doped Ga0.68In0.32NyAs1-y/GaAs single quantum well structures with various nitrogen concentrations has been studied. At low temperatures and low magnetic fields, in n-type samples negative and in p-type samples positive, magnetoresistance has been observed. The observed negative magnetoresistance in n-type samples is an indication of enhanced backscattering of electrons due to the weak localization of the electrons as an effect of the N-induced defects. Nitrogen concentration and thermal annealing dependence of the magnetoresistance have been studied for both n- and p-type samples. The observed decrease in the negative magnetoresistance in n-type and enhanced positive magnetoresistance in p-type samples following thermal annealing have been explained by considering thermal annealing-induced improvement of mobility and the crystal quality in N-containing samples. After thermal annealing, the magnitude of negative magnetoresistance decreases and the breaking of the weak localization is achieved at lower magnetic fields in n-type samples. It is observed that as the mobility of the sample increases, critical magnetic field of negative to positive magnetoresistance transition becomes lower.

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.

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.

International audience; We report on an investigation of optical and structural properties of as-grown and thermal annealed GaBixAs1−x (x = 0.012, 0.018 and 0.03) epilayers by photomodulated reflectance (PR) spectroscopy, atomic force microscopy (AFM) and micro-Raman spectroscopy. PR spectra are analyzed by third derivative functional form (TDFF) lineshape. Optical transition energies are calculated using strain-included valence band anticrossing (VBAC) model. According to the results, optical transitions are from conduction bandedge to heavy hole bandedge and to light hole bandedge, which are affected by compressive strain and effect of strain is clearly seen when Bi concentration exceeds 2%. We also determine the band-anticrossing interaction parameter CBiM as 1.33 eV. TDFF analysis of as-grown and thermal annealed samples reveal that thermal annealing causes an unexpectedly large redshift of ∼22 meV/Bi% in the bandgap that corresponds to the increase of Bi composition by ∼25% in the GaAs lattice. The origin of this redshift is analyzed by AFM and Raman spectroscopy. Surface morphology of the GaBiAs samples show that droplets appear on the GaBiAs surface and their sizes increase with increasing Bi concentration, but tend to decrease following thermal annealing process and some surface droplets leave pits in their locations. Raman spectroscopy and AFM results give hints of diffusion of some Bi atoms from surface into the epilayer that causes an increase in Bi concentration of the alloy. This increase explains the observed annealing-induced redshift of the bandgap in PR measurement.

Flavopiridol is a synthetically produced flavonoid that potently inhibits the proliferation of human tumor cell lines. Flavopiridol exerts strong antitumor activity via several mechanisms, including the induction of cell cycle arrest and apoptosis, and the modulation of transcriptional regulation. The aim of the present study was to determine the effect of flavopiridol on a subpopulation of cluster of differentiation (CD)44+/CD24− human breast cancer MCF7 stem cells. The CD44+/CD24− cells were isolated from the MCF7 cell line by fluorescence-activated cell sorting and treated with 100, 300, 500, 750 and 1,000 nM flavopiridol for 24, 48 and 72 h. Cell viability and proliferation assays were performed to determine the inhibitory effect of flavopiridol. Gene expression profiling was analyzed using Illumina Human HT-12 v4 Expression BeadChip microarray. According to the results, the half maximal inhibitory concentration (IC50) value of flavopiridol was 500 nM in monolayer cells. Flavopiridol induced growth inhibition and cytotoxicity in breast cancer stem cells (BCSCs) at the IC50 dose. The present study revealed several differentially regulated genes between flavopiridol-treated and untreated cells. The result of the pathway analysis revealed that flavopiridol serves an important role in translation, the ribosome biogenesis pathway, oxidative phosphorylation, the electron transport chain pathway, carbon metabolism and cell cycle. A notable result from the present study is that ribosome-associated gene expression is significantly affected by flavopiridol treatment. The data of the present study indicate that flavopiridol exhibits antitumor activity against CD44+/CD24− MCF7 BCSCs through different mechanisms, mainly by inhibiting translation and the ribosome biogenesis pathway, and could be an effective chemotherapeutic molecule to target and kill BCSCs.

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

The humidity-sensing properties of ZnO nanowires synthesized by carbothermal catalyst-free vapor solid (VS) technique were studied. The morphology and the crystal structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The humidity adsorption and desorption kinetics of the synthesized ZnO nanowires were investigated via quartz crystal microbalance (QCM) measurements. The observed positive frequency shift of ZnO nanowires when loaded on the QCM crystal under varying relative humidity conditions can be explained in terms of visco-elastic variations in their mechanical stiffness., Istanbul University (2526 and UDP 6728); State Planning Organization of Turkey (DPT2003K120390); Scientific and Technological Research Council of Turkey (TBAG 109T240)

We present the details of a proposed microwave kinetic inductance detector (MKID) for the DAG (Eastern Anatolia Observatory in Turkish) telescope, DAG-MKID. The observatory will have a modern 4m size telescope that is currently under construction. Current plan to obtain the first light with the telescope is late 2019. The proposed MKID based instrument will enable astronomers to simultaneously detect photons in the relatively wide wavelength range of 4000-13500 Å with a timing accuracy of μs and spectral resolution R = /▵ =10-25. With a planned field of view of approximately an arcminute, DAG-MKID will mostly be used for follow-up observations of transient or variable objects as well as a robust tool to measure photometric redshifts of a large number of galaxies or other extra-galactic objects. Publisher's Version

JAK/STAT is an evolutionarily conserved pathway and very important for second messenger system. This pathway is important in malignant transformation and accumulated evidence indicates that this pathway is involved in tumorigenesis and progression of several cancers. It was possible to assume that activation of JAK/STAT pathway is associated with increase in the expressions of ICAM/1 and VCAM-1. In this study we hypothesized that when cells were maintained as spheroids or monolayers, the structure of cancer stem cells (CSCs) could show differentiation when compared with non-CSCs.DU-145 human prostate cancer cells were cultured using the Ege University molecular embryology laboratory medium supplemented wıth 10% fetal bovine serum. Clusters of differentiation 133 (CD133)(+high)/CD44(+high) prostate CSCs were isolated from the DU145 cell line by using BD FACSAria. CD133//CD44+ CSCs were cultured until confluent with 3% noble agar. The expression of these proteins in CSCs and non-CSCs was analyzed by immunohistochemistry.Different expression profiles were observed in the conventional two-dimensional (2D) and three-dimensional (3D) experimental model system when CSCs and non-CSCs were compared. Human prostate CSCs exhibited intense ICAM-1 and VCAM-1 immunoreaction when compared with non-CSCs. These findings were supported by the fact that VCAM-1 on the surface of cancer cells binds to its counterreceptor, the α4β1 integrin (also known as very-late antigen, VLA-4), on metastasis-associated macrophages, triggering VCAM-1-mediated activation of the phosphoinositide 3-kinase growth and survival pathway in cancer cells.The results of this study showed that changes in JAK/STAT pathway are related with adhesion molecules and could affect cancer progression.

International audience; In this study, molecular beam epitaxial-grown GaAs/GaBiAs single quantum well systems with two different Bi contents were investigated. Spectral dependence of room temperature photomodulated reflectance (PR) and photoluminescence (PL) measurements in the temperature range of 35–300 K were employed. PR spectra indicate that increasing Bi concentration promotes a tendency to approach quantized higher energy levels in the heavy and light holes' bands due to the different effects of compressive strain, which depends on Bi concentrations. In addition, a defect level is identified at 0.71 eV at room temperature PR spectra and is attributed to a AsGa antisite defect in GaAs barrier layers caused by the low temperature growth process. From the analysis of the temperature dependence of emission energy and amplitude in the PL spectra, localized states are determined in the range of 8 to 45 meV and attributed to the different bonding configuration of Bi clusters. Low temperature PL results imply that Bi cluster states tend to move into the valance band when Bi content increases from 2.4 to 7.0% in the GaBiAs system.

AIM: The aim of this study was to provide retrospective information about the prescribed drugs among pregnant woman who referred to Ege University Department of Pharmacology and Clinical Pharmacology. MATERIAL-METHOD: A retrospective study was conducted among pregnant woman who referred to our department between January 1, 2005 and December 31, 2005. Initially, all women were evaluated by an obstetrician and and the effects of the drugs during pregnancy was determined according to the United States Food and Drug Administration (FDA) risk classification system database RESULTS: 345 pregnant women were evaluated during the study. 43 % of the women were referred from Ege University Medical Faculty Department of Obstetrics and Gynaecology and 24 % from public hospitals, whereas 33% were consigned from doctor offices. 30% of the women were between 25-29 years of age. The most commonly prescribed drugs were anti-infectives (26.6 %), opioid and non-opioid analgesics (18.3%), antidepressants (8.4%) and flu medications (8.2 %). According to the FDA classification 1.4% of the prescribed drugs were in category A, 42.9% were in category B, 42.4% were in category C, 6.7% were in category D and 3.1% were in category X. 83.6% of the pregnant women had medications during first trimester of their pregnancies. Only 10% of the women received a single drug. CONCLUSIONS: Our study reveals that during their pregnancies an important proportion of women encounter drugs which might have a teratogenic potential. This proportion. can be reduced by interrogation of the patient about pregnancy before prescribing drugs.

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 have performed magnetoresistance measurements on n- and p-type modulation doped GaInNAs/GaAs quantum well (QW) structures in both the weak (B < 0.08 T) and the high magnetic field (up to 18 T) at 75 mK and 6 K. We observe that the quantum oscillations in rho(xx) and quantum Hall effect (QHE) plateaus in rho(xy) are affected from the presence of the nitrogen in the III-V lattice. The enhancement of n- related scatterings and electron effective mass with increasing nitrogen causes lower electron mobility and higher two-dimensional (2D) electron density, leading to suppressed QHE plateaus in rho(xy) up to 7 T at 6 K. The Shubnikov de Haas (SdH) oscillations develop at lower magnetic fields for higher mobility samples at 6 K and the amplitude of SdH oscillations decreases with increasing nitrogen composition. The well-pronounced QHE plateaus are observed at 75 mK and at higher magnetic fields up to 18 T, for the p-type sample. For n- type samples, the observed anomalies in the characteristic of QHE is attributed the nitrogen-related disorders and overlapping of fluctuating Landau levels. The low magnetic field measurements at 75 mK reveal that the n-type samples exhibit weak antilocalization, whereas weak localization is observed for the p-type sample. The observation of weak antilocalization is an indication of strong electron spin-orbit interactions. The low field magnetoresistance traces are used to extract the spin coherence, phase coherence and elastic scattering times as well Rashba parameters and spin-splitting energy. The calculated Rashba parameters for nitrogen containing samples reveal that the nitrogen composition is a significant parameter to determine the degree of the spin-orbit interactions. Consequently, GaInNAs-based QW structures with various nitrogen compositions can be beneficial to adjust the spin-orbit coupling strength and may be used as a candidate for spintronics applications.

The electron Lande g factor (g∗) is investigated both experimentally and theoretically in a series of GaBixAs1−x/GaAs strained epitaxial layers, for bismuth compositions up to x=3.8%. We measure g∗ via time-resolved photoluminescence spectroscopy, which we use to analyze the spin quantum beats in the polarization of the photoluminescence in the presence of an externally applied magnetic field. The experimental measurements are compared directly to atomistic tight-binding calculations on large supercells, which allows us to explicitly account for alloy disorder effects. We demonstrate that the magnitude of g∗ increases strongly with increasing Bi composition x and, based on the agreement between the theoretical calculations and experimental measurements, elucidate the underlying causes of the observed variation of g∗. By performing measurements in which the orientation of the applied magnetic field is changed, we further demonstrate that g∗ is strongly anisotropic. We quantify the observed variation of g∗ with x, and its anisotropy, in terms of a combination of epitaxial strain and Bi-induced hybridization of valence states due to alloy disorder, which strongly perturbs the electronic structure.

Temperature and nitrogen dependence of 2D carrier mobility in as-grown and annealed Ga1-xInxNyAs1-y/GaAs quantum well (QW) structures (x = 0.32; y = 0, 0.009, and 0.012) are investigated. An analytical model that accounts for the most prominent scattering mechanisms is used to explain the characteristic of temperature dependence of the carrier mobility. An expression for alloy scattering-limited mobility in N-related alloys is developed to explain the behavior of hole mobility for N-containing p-type samples. Analytical modeling of temperature dependence of the electron mobility indicates that N-related alloy scattering and interface roughness scattering are the dominant mechanism at the entire temperature range of interest. The temperature insensitivity of the electron mobility is explained in terms of the overriding effect of N-related alloy scattering and high 2D electron density. A deviation between theoretical and experimental electron mobility at low temperatures is observed not to have any dependency on N concentration. We, therefore, suggest that C-NM interaction parameter of the band anti-crossing (BAC) model must be defined as temperature dependent in order to explain the observed low temperature characteristics of electron mobility. The hole mobility is mainly restricted by interface roughness and alloy scatterings at temperatures lower than 100 K, whilst high temperature hole mobility is drastically affected from optical phonon scattering. Moreover, the hole mobility at high temperatures exhibits an N-independent characteristic and hole density starts to increase at temperatures above 70 K, which is explained using the concept of parallel conduction. Extraction of the hole density in each transport channel (QW and barrier) by using a simple parallel conduction extraction method (SPCEM) shows that, in p-type samples, low temperature hole mobility takes place in quantum well, while as temperature increases barrier channel also contribute to the hole mobility and becomes dominant at high temperatures. The experimental and calculated Hall mobility results reveal that thermal annealing has decreased interface roughness and alloy scatterings.

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.

Nitrogen dependence of hole effective mass and hole mobility in p-type modulation doped Ga0.68In0.32NyAs1-y/GaAs quantum well structures with y = 0, 0.009, 0.012, 0.017 are investigated using magnetotransport and Hall effect measurements. Observed N-dependent reduction of the hole effective mass is explained by stronger confinement of holes. Hole effective mass is also found to have hole density dependence due to the strain-induced valance band non-parabolicity. A tendency to decrease in hole effective mass upon annealing can be attributed to the reduction of well width and/or decrease in hole density. A significant improvement in low temperature hole mobility is observed after annealing. (C) 2013 AIP Publishing LLC.

In this study, we investigate the effect of annealing and nitrogen amount on electronic transport properties in n- and p-type-doped Ga0.68In0.32N y As1 − y /GaAs quantum well (QW) structures with y = 0%, 0.9%, 1.2%, 1.7%. The samples are thermal annealed at 700°C for 60 and 600 s, and Hall effect measurements have been performed between 10 and 300 K. Drastic decrease is observed in the electron mobility of n-type N-containing samples due to the possible N-induced scattering mechanisms and increasing effect mass of the alloy. The temperature dependence of electron mobility has an almost temperature insensitive characteristic, whereas for p-type samples hole mobility is decreased drastically at T > 120 K. As N concentration is increased, the hole mobility also increased as a reason of decreasing lattice mismatch. Screening effect of N-related alloy scattering over phonon scattering in n-type samples may be the reason of the temperature-insensitive electron mobility. At low temperature regime, hole mobility is higher than electron mobility by a factor of 3 to 4. However, at high temperatures (T > 120 K), the mobility of p-type samples is restricted by the scattering of the optical phonons. Because the valance band discontinuity is smaller compared to the conduction band, thermionic transport of holes from QW to the barrier material, GaAs, also contributes to the mobility at high temperatures that results in a decrease in mobility. The hole mobility results of as-grown samples do not show a systematic behavior, while annealed samples do, depending on N concentration. Thermal annealing does not show a significant improvement of electron mobility.

WOS: 000312586500001, PubMed ID: 23075073, We report on the Mg-doped, indium-rich Ga (x) In1-x N (x < 30). In the undoped material, the intrinsic electron density is very high and as a result there is no detectable photoconductivity (PC) signal within the range of temperatures of 30 < T < 300 K. In the Mg-doped material however, where the conductivity is reduced, there is a strong PC spectrum with two prominent low-energy peaks at 0.65 and 1.0 eV and one broad high-energy peak at around 1.35 eV. The temperature dependence of the spectral photoconductivity under constant illumination intensity, at T > 150 K, is determined by the longitudinal-optical phonon scattering together with the thermal regeneration of non-equilibrium minority carriers from traps with an average depth of 103 +/- 15 meV. This value is close to the Mg binding energy in GaInN. The complementary measurements of transient photoluminescence at liquid He temperatures give the e-A(0) binding energy of approximately 100 meV. Furthermore, Hall measurements in the Mg-doped material also indicate an activated behaviour with an acceptor binding energy of 108 +/- 20 meV., TUBITAK Ankara [EEEAG-105E076]; Istanbul University [9571]; COST Action [MP 0805], We are grateful to WJ Schaff for the samples, to TUBITAK Ankara for the funding (project number EEEAG-105E076) and to Istanbul University for the funding (project number 9571). We also acknowledge the COST Action MP 0805 for funding the international scientific collaboration.

WOS: 000308271400022, I-V characterization of an n-type quantum well infrared photodetector which consists of stepped and graded barriers has been clone under dark at temperatures between 20-300 K. Different current transport mechanisms and transition between them have been observed at temperature around 47 K. Activation energies of the electrons at various bias voltages have been obtainer, from the temperature dependent I-V measurements. Activation energy at zero bias has been calculated by extrapolating the bias dependence of the activation energies. Ground state energies and barrier heights of the four different quantum wells have been calculated by using an iterative technique, which depends on experimentally obtained activation energy. Ground state energies also have been calculated with transfer matrix technique and compared. with iteration results. Incorporating the effect of high electron density induced electron exchange interaction on ground state energies; more consistent results with theoretical transfer matrix calculations have been obtained, Scientific and Technological Research Council of Turkey (TUBITAK) [108T721]; COST Action [MP0805]; Scientific Research Projects Coordination Unit of Istanbul University [3587], This work 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.

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.

Effects of high electron concentration on the band gap energy of InN films having different layer thicknesses as 600 and 800 nm are investigated experimentally and theoretically. Electron concentrations of the samples are obtained through the Hall measurements accomplished between 77K and room temperature. Optical characterization of the samples is carried out using the photoluminescence (PL) measurements and the observed PL spectra are explained considering the high electron concentration related effects, i.e. Burstein-Moss shift, band renormalization and band tailing in non-parabolic k.p model. Extracted PL results indicate that the samples have approximately 0.685 eV band gap energy at 77 K. Effective mass of the carriers, which is calculated as 0.097m(0) for electron concentration of similar to 10(19) cm(-3), are also observed to be influenced by the high carrier concentration. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

WOS: 000275763100028, ZnO nanoparticles have been synthesized by the sol-gel method with approximately 10 nm diameter and the humidity adsorption and desorption kinetics of ZnO nanoparticles were investigated by quartz crystal microbalance (QCM) technique. The morphology and crystal structure of the ZnO nanoparticles have been characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The roughness of the surface has been investigated using atomic force microscope (AFM). The dynamic Langmuir adsorption model was used to determine the kinetic parameters such as adsorption and desorption rates and Gibbs free energy under relative humidity between 45% and 88%. The relative sensitivity of the ZnO nanoparticles-based humidity sensor was determined by electrical resistance measurements. Our reproducible experimental results show that ZnO nanoparticles have a great potential for humidity sensing applications at room temperature operations. (C) 2009 Elsevier B.V. All rights reserved., Research Fund of the Istanbul UniversityIstanbul University [2526, UDP 3670], This work was supported by Research Fund of the Istanbul University. Project number: 2526 and Project number: UDP 3670.