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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

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.

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.

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.

Colorectal cancer is the third most common cancer worldwide. Cancer stem cells are known to play an important role in relapse, and metastases of the disease after chemotherapy. Investigation of new drugs, and their combinations targeting these cells and thus eliminating cancer is one of the most urgent needs of today’s chemotherapy. The aim of the present study was to evaluate the effects of Bryophytes like Abietinella abietina (AA), Homolothecium sericeum (HS), Tortella tortuosa (TT), Syntrichia ruralis (SR), and Bryoerythrophyllum rubrum (BR) species extracted with ethyl alcohol on 5-fluorouracil(5-FU) resistant colorectal cancer cell lines (HCT116 and HT29). After extraction, stock solutions of bryophytes were prepared, and IC50 values were detected in drug-resistant cells obtained with 5-FU application. CD24+, CD44+/CD133+ surface markers and P‐glycoprotein (P-gp) mediated efflux were isolated from both 5-FU treated cells and analyzed using the flow cytometry. In all bryophyte-treated groups, the binding Rho123low (low Rho fluorescence) and Rhohigh (high Rho fluorescence) were sorted from 5-FU resistant HCT116, and HT-29 cells. All types of bryophytes were found cytotoxic. Bryophyte extract reduced the percentage of Rholow cells in cultures incubated with 5-FU. In summary, the implementation of these bryophytes might be regarded as an effective approach for treatment of colorectal cancer due to their cytotoxic effect that decreases the recurrence of the disease. WOS:000664604500001 34151658 Q3

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

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 integer quantum Hall Effect (QHE) and magnetoresistance measurements are carried out at temperature range 1.8 K and 40 K under a magnetic field up to 11 T to investigate the influence of the thermal annealing process and thermal annealing time on the transport parameters of as-grown and annealed n-type Ga0.68In0.32N0.017As0.983/GaAs quantum well (QW) structures. The electron effective mass, two-dimensional (2D) carrier density, quantum lifetime, and Fermi level are obtained by analyzing both oscillatory parts of magnetoresistance measurements (Shubnikov de Haas oscillations) and QHE oscillations. The compatibility of two different methods with each other is discussed, and the dependence of physical parameters obtained from both methods on annealing time was discussed. Our results reveal that the thermal annealing process and annealing duration time affect 2D carrier density, electron effective mass, quantum lifetime, transport lifetime, and Fermi level. The increase in annealing time showed that μ t / μ q ratios caused the shift from long-range scattering to short-range scattering in the low-temperature region.

We have studied the temperature-dependent optical absorption and emission mechanisms of ternary chalcogenide TlSbS2 by carrying out sandwich and planar photoconductivity, and photoluminescence measurements in the temperature range 30 K to 300 K. Two main transitions were observed in the room temperature photoconductivity spectrum at energies of 1.74 and 1.84 eV, which are attributed to a native acceptor–donor transition and a band-to-band transition, respectively. A spectral anisotropy near the bandgap energy of TlSbS2 is observed between the sandwich and in-plane photoconductivity spectrum. In the photoluminescence spectrum, we observed deep-level broadband emission which is correlated with the native defect-related transition-based free-to-bound recombination between 30 K and 70 K. The Debye temperature of TlSbS2 was found to be 280 K, and the thermal expansion coefficient was determined as 1.62 × 10 - 3 e V / K from the analyses of its temperature-dependent photoconductivity spectra.

Poly (3,4-ethylenedioxythiophene)-poly (styrene sulfonate (PEDOT:PSS) is a widely-known conductive polymer mixture that is mostly engaged as a hole transport layer (HTL) in organic and perovskite solar cells (PSCs). In this study, it has been demonstrated that the use of Zn as an additive in PEDOT:PSS solution improved the photovoltaic performance of the ambient air solution-based fabrication of methylammonium lead tri-iodide (MAPbI3) based devices. The short circuit current density (JSC) of the device increased from 15.4 to 17.2 mA/cm2, while the fill factor (FF) improved from 0.70 to 0.83 by using Zn-doped PEDOT:PSS as a hole transport layer (HTL), which is a record value for only γ-butyrolactone (GBL) based MAPbI3 PSCs. Additionally, open-circuit (VOC) value is boosted up from 890 to 925 mV by Zn-doping, which might be linked to the increased work function of the investigated HTLs. Moreover, the synergetic effect of improved electrical conductivity and hole mobility of PEDOT:PSS film and decreased the trap density of perovskite led to an increase of 37% in power conversion efficiency (PCE) and the stability of the inverted planar PSCs.

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.

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.

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

A GaAs1-xBix layer was grown by molecular beam epitaxy (MBE) with a low Bi content (2.3%) on GaAs maintaining the substrate at a non-rotating state and was then annealed at 750 °C, 800 °C and 850 °C. Each sample that was covered with droplets was investigated by using the Atomic Force Microscopy (AFM), Electrostatic Force Microscopy (EFM) and Photoluminescence (PL) techniques. The surface properties of the GaAs1-xBix layer were investigated by AFM and observed to have a droplet system, which was composed of a donut and a tail. The optical quality of the samples was enhanced after thermal annealing up to 800 °C, and the maximum PL intensity was obtained at 750 °C. AFM images revealed that the shape of the droplet and tail changed with increasing annealing temperature. EFM images revealed a phase separation on the surface droplet system. To explore the nature of the droplets, previously claimed to be made of Ga and/or Bi, and their effect on PL spectrum, a chemical etch procedure was carried out by using diluted solutions of H₂SO₄ and/or HCl. We showed that droplets may be efficiently removed from the surface, and PL intensity could be improved by using a proper sequence of chemical etching procedures. Furthermore, the presence of two different phases for the droplet-system observed by EFM was also confirmed by the selective etching procedure.

We report on the power loss mechanisms of hot carries in as-grown and annealed n- and p-type modulation-doped GaAs/Ga0.68In0.32NyAs1-y (y = 0.009, and 0.012) quantum well structures considering acoustic phonon interactions via the deformation potential (non-polar) and piezoelectric (polar) scatterings. By analysis of the applied electric field dependent amplitude of the Shubnikov de Haas oscillations, it has been revealed that incorporation of N atom into Ga0.68In0.32As switches the dominant power loss mechanism from non-polar to polar mechanism. The piezoelectricity of n- and p-type Ga0.68In0.32NyAs1-y alloys is at least three times higher than N-free samples. A comparison between as-grown n- and p-type samples depicts that the p-type sample's piezoelectricity is higher than that of n-type samples. After thermal annealing, there is a slight decrement and increment in piezoelectric stress constant for n-type the sample with 0.9% and 1.2% N, respectively.

Hot electrons relax by interacting with phonons, so information about the electron-phonon interaction mechanisms are obtained by examining the cooling processes of hot electrons. In this study, the effect of annealing time on the electron temperature and energy relaxation rates in as-grown and annealed n-type modulation-doped Ga0.68In0.32N0.017As0.983/GaAs quantum well (QW) samples were investigated by comparing the relative amplitudes of Shubnikov-de Haas oscillations as a function of temperature and electric field. The samples were grown by molecular beam epitaxy (MBE) and annealed at 700 °C for 60 s and 600 s. Experiments were carried out by applying an electric field between 0.165 and 5.276 kV/m at a temperature range between 1.8 and 40 K under magnetic up to 11 T. The energy-relaxation mechanism is found to be a mixing of piezoelectric and deformation potential scatterings of hot electrons in the low-temperature regime up to 40 K electron temperature. The electron power loss by interacting with phonons is characterized with exponential term γ, which is found to be in the range from 3.42 to 4.97. The change of γ showed that the scattering mechanisms are affected by the annealing time. The piezoelectric stress constant (e14) chosen as a fit parameter in the theoretical power loss calculations, which was found between 0.129 and 0.134. The crystal quality at low temperatures has been observed to be effective on energy relaxation times.

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.

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 (