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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.

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

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, 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).

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.

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

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

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.

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

WOS: 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.

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.

Teke, Ali (Balikesir Author), We have investigated in-plane photovoltage (IPV) and photoluminescence (PL) in sequentially grown Ga0.8In0.2As/GaAs and Ga0.8In0.2N0.015As0.985/GaAs-quantum wells. Temperature, excitation intensity, spectral and time dependent study of the IPV, arising from Fermi level fluctuations along the layers of the double quantum well structure, gives valuable information about the nonradiative centers and hence about the optical quality of the GaInNAs quantum well. It also provides information about the radiative transition energies in all the layers. In order to obtain either the trap activation energies and the detrapping rates of photogenerated carriers in the GaInNAs the IPV results are analyzed,in terms of a theoretical model based on random doping fluctuations in nominally undoped multilayer structures. The PL results are analyzed in terms of the band anticrossing model to obtain the electron effective mass from the coupling parameter C-NM

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

Electronic transport in unintentionally doped GaxIn1-xN alloys with various Ga concentrations (x = 0.06, 0.32 and 0.52) is studied. Hall effect measurements are performed at temperatures between 77 and 300 K. Temperature dependence of carrier mobility is analysed by an analytical formula based on two-dimensional degenerate statistics by taking into account all major scattering mechanisms for a two-dimensional electron gas confined in a triangular quantum well between GaxIn1-xN epilayer and GaN buffer. Experimental results show that as the Ga concentration increases, mobility not only decreases drastically but also becomes less temperature dependent. Carrier density is almost temperature independent and tends to increase with increasing Ga concentration. The weak temperature dependence of the mobility may be attributed to screening of polar optical phonon scattering at high temperatures by the high free carrier concentration, which is at the order of 1014 cm−2. In our analytical model, the dislocation density is used as an adjustable parameter for the best fit to the experimental results. Our results reveal that in the samples with lower Ga compositions and carrier concentrations, alloy and interface roughness scattering are the dominant scattering mechanisms at low temperatures, while at high temperatures, optical phonon scattering is the dominant mechanism. In the samples with higher Ga compositions and carrier concentrations, however, dislocation scattering becomes more significant and suppresses the effect of longitudinal optical phonon scattering at high temperatures, leading to an almost temperature-independent behaviour.

Bulk GaAs1 - x Bi x /GaAs alloys with various bismuth compositions are studied using power- and temperature-dependent photoluminescence (PL), Raman scattering, and atomic force microscopy (AFM). PL measurements exhibit that the bandgap of the alloy decreases with increasing bismuth composition. Moreover, PL peak energy and PL characteristic are found to be excitation intensity dependent. The PL signal is detectable below 150 K at low excitation intensities, but quenches at higher temperatures. As excitation intensity is increased, PL can be observable at room temperature and PL peak energy blueshifts. The quenching temperature of the PL signal tends to shift to higher temperatures with increasing bismuth composition, giving rise to an increase in Bi-related localization energy of disorders. The composition dependence of the PL is also found to be power dependent, changing from about 63 to 87 meV/Bi% as excitation intensity is increased. In addition, S-shaped temperature dependence at low excitation intensities is observed, a well-known signature of localized levels above valence band. Applying Varshni’s law to the temperature dependence of the PL peak energy, the concentration dependence of Debye temperature (β) and thermal expansion coefficient (α) are determined. AFM observations show that bismuth islands are randomly distributed on the surface and the diameter of the islands tends to increase with increasing bismuth composition. Raman scattering spectra show that incorporation of Bi into GaAs causes a new feature at around 185 cm-1 with slightly increasing Raman intensity as the Bi concentration increases. A broad feature located between 210 and 250 cm-1 is also observed and its intensity increases with increasing Bi content. Furthermore, the forbidden transverse optical (TO) mode becomes more pronounced for the samples with higher bismuth composition, which can be attributed to the effect of Bi-induced disorders on crystal symmetry. PACS 78.55Cr 78.55-m 78.20-e 78.30-j

WOS: 000312087300001, PubMed ID: 23113959, Within the envelope function approach and the effective-mass approximation, we have investigated theoretically the effect of an intense, high-frequency laser field on the bound states in a Ga (x) In1 - x N (y) As1 - y /GaAs double quantum well for different nitrogen and indium mole concentrations. The laser-dressed potential, bound states, and squared wave functions related to these bound states in Ga1 - x In (x) N (y) As1 - y /GaAs double quantum well are investigated as a function of the position and laser-dressing parameter. Our numerical results show that both intense laser field and nitrogen (indium) incorporation into the GaInNAs have strong influences on carrier localization., Scientific and Technological Research Council of Turkey (TUBITAK) [COST 109 T650]; Scientific Research Project Fund of Cumhuriyet University [F-360], This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) for a research grant COST 109 T650 and was partially supported by the Scientific Research Project Fund of Cumhuriyet University under the project number F-360.

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

The excitation energy-dependent nature of Raman scattering spectrum, vibration, electronic or both, has been studied using different excitation sources on as-grown and annealed n- and p-type modulation-doped Ga1 − xIn x N y As1 − y/GaAs quantum well structures. The samples were grown by molecular beam technique with different N concentrations (y = 0%, 0.9%, 1.2%, 1.7%) at the same In concentration of 32%. Micro-Raman measurements have been carried out using 532 and 758 nm lines of diode lasers, and the 1064 nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the 785 and 1064 nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the 532 nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of 532 nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. The results exhibited that the nature of the Raman scattering spectrum is strongly excitation energy-dependent, and with suitable excitation energy, electronic and/or vibrational transitions can be investigated.

We report the observation of thermal annealing- and nitrogen-induced effects on electronic transport properties of as-grown and annealed n- and p-type modulation-doped Ga1 - x In x N y As1 - y (x = 0.32, y = 0, 0.009, and 0.012) strained quantum well (QW) structures using magnetotransport measurements. Strong and well-resolved Shubnikov de Haas (SdH) oscillations are observed at magnetic fields as low as 3 T and persist to temperatures as high as 20 K, which are used to determine effective mass, 2D carrier density, and Fermi energy. The analysis of temperature dependence of SdH oscillations revealed that the electron mass enhances with increasing nitrogen content. Furthermore, even the current theory of dilute nitrides does not predict a change in hole effective mass; nitrogen dependency of hole effective mass is found and attributed to both strain- and confinement-induced effects on the valence band. Both electron and hole effective masses are changed after thermal annealing process. Although all samples were doped with the same density, the presence of nitrogen in n-type material gives rise to an enhancement in the 2D electron density compared to the 2D hole density as a result of enhanced effective mass due to the effect of nitrogen on conduction band. Our results reveal that effective mass and 2D carrier density can be tailored by nitrogen composition and thermal annealing-induced effects. PACS 72.00.00; 72.15.Gd; 72.80.Ey