İstanbul Üniversitesi
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Research Laboratories Information System
Yüksek Manyetik Alan ve Düşük Sıcaklık Laboratuvarı
Yüksek Manyetik Alan ve Düşük Sıcaklık Laboratuvarı
Laboratuvar altyapısı ve cihaz donanımı İstanbul Üniversitesi desteği ile sağlanarak 2012 yılında kurulmuş olan Yüksek Manyetik Alan ve Düşük Sıcaklık Laboratuvarı, katı malzemelerin ve yarıiletken aygıtların değişken manyetik alan ve düşük sıcaklıklarda yük taşınım mekanizmalarının incelenmesi, iletkenliğin manyetik alana bağlı değişimi, klasik Hall Olayı ve kuantum Hall olayı, elektriksel karakterizasyon ve manyetik özelliklerin incelenmesine dayalı çalışmalar yürütülmesine uygun donanıma sahiptir.
İstanbul Üniversitesi, Fen Fakültesi, Fizik Bölümü, Katıhal Fiziği Anabilim Dalı, 34134, Vezneciler, Fatih, İstanbul TÜRKİYE
Toplam kullanılan BAP Kaynağı: 4.857.856,51 TL
Laboratuvar altyapısı ve cihaz donanımı İstanbul Üniversitesi desteği ile sağlanarak 2012 yılında kurulmuş olan Yüksek Manyetik Alan ve Düşük Sıcaklık Laboratuvarı, katı malzemelerin ve yarıiletken aygıtların değişken manyetik alan ve düşük sıcaklıklarda yük taşınım mekanizmalarının incelenmesi, iletkenliğin manyetik alana bağlı değişimi, klasik Hall Olayı ve kuantum Hall olayı, elektriksel karakterizasyon ve manyetik özelliklerin incelenmesine dayalı çalışmalar yürütülmesine uygun donanıma sahiptir.
Laboratuvarda Seyreltme soğutucu sistemli (250 mK - HELIOX VL) 18/20 T süperiletken magnet, helyum geri dönüşüm ve 18lt/gün kapasiteli helyum sıvılaştırıcı sistemine sahibiz.
Essex Üniversitesi (İngiltere), Tampere Teknik Üniversitesi (Finlandiya), LAAS (Fransa), INSA (Fransa), Victoria Üniversitesi (Kanada) ve Delaware Üniversitesi (Amerika Birleşik Devletleri) ile işbirlikleri kapsamında yarıiletken malzemelerin manyetik özelliklerinin incelenmesi, klasik ve kuantum Hall olayı, katılarda yük taşınımına dayalı projeler yürütülmesi hedeflenmektedir.
İstanbul Üniversitesi, Fen Fakültesi, Fizik Bölümü, Katıhal Fiziği Anabilim Dalı, 34134, Vezneciler, Fatih, İstanbul TÜRKİYE
Toplam kullanılan BAP Kaynağı: 4.857.856,51 TL
High Magnetic Field and Low Temperature Laboratory
Laboratory of High Magnet-ic Field and Low Temperatures, founded in 2012 by provision of laboratory infrastructure and equipment with the support of İstanbul University, is suitably equipped to enable studies on in-vestigation of charge transport mechanisms of solid materials and semiconductor devices at a varia-ble magnetic field and low temper-atures, magnetic field-dependent conductivity, classical Hall Phe-nomenon and quantum Hall Phenomenon, electrical characterization and investigation of magnetic properties.
We have 18/20 T Superconducting magnet with dilution refrigerator system (250 mK - HELIOX VL ), helium re-cycling system and helium liquefier system (18 l/day)
Istanbul University, Science Faculty, Physics Department, Solid State Physics Division, 34134, Vezneciler, Fatih, Istanbul TURKEY
Total resource (BAP): 4.857.856,51 TL
Laboratory of High Magnet-ic Field and Low Temperatures, founded in 2012 by provision of laboratory infrastructure and equipment with the support of İstanbul University, is suitably equipped to enable studies on in-vestigation of charge transport mechanisms of solid materials and semiconductor devices at a varia-ble magnetic field and low temper-atures, magnetic field-dependent conductivity, classical Hall Phe-nomenon and quantum Hall Phenomenon, electrical characterization and investigation of magnetic properties.
We have 18/20 T Superconducting magnet with dilution refrigerator system (250 mK - HELIOX VL ), helium re-cycling system and helium liquefier system (18 l/day)
We aim to initiate and run collaborative studies and projects with University of Essex (England), Tampere University of Technology (Finland), LAAS (France), INSA (France), Victoria University (Canada) and Unıversity of Delaware ( United States of America) based on investigation of magnetic properties of semiconduc-tor materials, classical and quantum Hall Phenomenon, charge transport in solids.
Istanbul University, Science Faculty, Physics Department, Solid State Physics Division, 34134, Vezneciler, Fatih, Istanbul TURKEY
Total resource (BAP): 4.857.856,51 TL
Cihaz Adı : Gaussmetre
Marka : Cyromech
Model : GM 700
Teknik Özellik : Belirtilmemiş
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Baskül
Marka : Belirtilmemiştir.
Model : Belirtilmemiştir.
Teknik Özellik : Belirtilmemiştir.
Miktar : 1
Cihaz Kaynağı : TÜBİTAKCihaz Adı : Dijital Multimetre
Marka : KEİTHLEY
Model : DMM 2000
Teknik Özellik : Dijital multimetre, Akım, Voltaj, Ohm, Frekans ölçümleri, GPIB kontrol
Miktar : 2
Cihaz Kaynağı : BAPCihaz Adı : Süper İletken Magnet ve Düşük Sıcaklık Sistemi
Marka : OXFORD INSTRUMENTS
Model : HELIOX VL-A, Kelvinox TLM 400 (Yedek olarak kullanılmaktadır.)
Teknik Özellik : Süper iletken magnet, 18/20 Tesla Manyetik alan, 10mK/250mK düşük sıcaklık değeri
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Helyum Sıvılaştırıcı ve Geri Dönüşüm Sistemi
Marka : CRYOMECH
Model : LHeP18
Teknik Özellik : Sıvı Helyum üretimi 18 litre/24saat, JORDAIR, BAUER Gaz Helyum depolama kompresör sistemi ve Helyum tüpleri (10 adet)
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Helyum Kaçak Test Dedektörü
Marka : Invicon
Model : UL1000
Teknik Özellik : He3, He4 vacuum and sniffing leak detection
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Turbo Moleküler Pompa Sistemi
Marka : Pfeiffer
Model : PM S20 230 00
Teknik Özellik : Hipace 80 Classic Turbo pompa, DUO 5M çift kademe Rotay Pompa, DCU Kontrol birimi,PKR 251 Full Range cold cathode Gauge,
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Rotary Pompası
Marka : Edwards
Model : 5M
Teknik Özellik : 2x10-3mbar ultimatepressure, 3.9 m3/hour pumping speed
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Sıvı Helyum Tankı
Marka : International Cryogenics
Model : SR500
Teknik Özellik : 100 Litre Kapasiteli
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Sıvı Azot Tankı
Marka : International Cryogenics
Model : Belirtilmemiştir.
Teknik Özellik : 100 litre kapasite
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Kapalı Devre su soğutma sistemi( Chiller)
Marka : Protect
Model : Protect300
Teknik Özellik : 25.900btu/hour soğutma kapasitesi, 2.7 kW soğutma gücü, 1.3 m3/hour su akış kapasitesi
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Sanayi Tüpü 50 litre Hacimli (Azot Gazı için)
Marka : Yalız
Model : Belirtilmemiştir.
Teknik Özellik : 200 Bar basınç, Azot Gazı uyumlu tüp
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Sanayi Tüpü 50 Litre Hacimli (Helyum Gazı için)
Marka : Markasız
Model : Belirtilmemiştir.
Teknik Özellik : 200 Bar basınç, Helyum Gazı uyumlu tüp
Miktar : 10
Cihaz Kaynağı : BAPCihaz Adı : Lock-in Amplifier
Marka : STANFORD
Model : SR810
Teknik Özellik : 2 Tesla, 9-300 Kelvin
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Transpalet
Marka : Belirtilmemiştir.
Model : Belirtilmemiştir.
Teknik Özellik : 2000 kg
Miktar : 1
Cihaz Kaynağı : BAPCihaz Adı : Precision Source/Measureunit
Marka : Agilent
Model : B2902A
Teknik Özellik : 100fA resolution, 3A DC / 10.5A Puls
Miktar : 1
Cihaz Kaynağı : BAP
- Makale & Yayın (31)
- Sanayi İşbirliği (1)
- Patent (1)
- Dış Kaynaklı Çalışma (0)
- Faydalı Model (0)
- Ticarileşme (0)
- Proje (5)
pp12pp
- Adı : Enhancement of light emission characteristic of a GaAs-based Gunn light emitting diode with a quasi-cavity
Açıklama : We report on a novel GaAs-based quasi-cavity enhanced Gunn light emitting diode (GLED) with a planar architecture operating at around 876 nm. GLED device was fabricated using an n-type GaAs epilayer with and without bottom 20 pairs of Al0.1Ga0.9As/AlAs distributed Bragg reflectors (DBRs) to investigate the influence of the incorporated bottom DBRs on emission characteristic of the Gunn device. The devices start emitting when Gunn oscillations with a frequency of 1 GHz emerges at the negative differential resistance (NDR) threshold at 3 kV/cm. Light intensity-electric field characteristic of both GLEDs with and without DBRs shows an abrupt increase in emitted light intensity at NDR threshold. The full-width at half maximum (FWHM) of the electroluminescence (EL) spectrum is reduced from 30 nm to 14 nm, and emitted light intensity is enhanced by about four times of magnitude compared with the GaAs-GLED without a quasi-cavity. The period of Gunn oscillations is found to be 1ns (f = 1 GHz). Divergence of the emitted light from GaAs-GLED with a quasi-cavity is found to be lower than that from basic GaAs-GLED device. EL mapping images prove that as increasing applied electric field, EL intensity enhances and spans almost the whole sample surface with a higher intensity in the vicinity of the anode of the device as an indication of growing and propagating Gunn domain along the device. Our results reveal that the GLED with a quasi-cavity operates with a higher spectral purity. DOI: 10.1016/j.mssp.2023.107877
Ekip : Selman Mutlu, Goksenin Kalyon, Fahrettin Sarcan , Omer Goksel Erbas, Ayse Erol - Adı : Effects of annealing temperature on a ZnO thin film-based ultraviolet photodetector
Açıklama : In this paper, the effects of annealing temperature on the performance of a ZnO thin film-based Metal-Semiconductor-Metal (MSM) type ultraviolet (UV) photodetector is reported. ZnO thin films were grown on a glass substrate using the Pulsed Filtered Cathodic Vacuum Arc Deposition (PFCVAD) technique at room temperature and after the deposition process the samples were annealed at 400, 450 and 550 °C in air condition to investigate the annealing effect on the structural, electrical, and optical properties of the photodetector. ZnO thin films which have grains in nanometer range has an increasing in the diameter of grains from 10.5 to 18.3 nm as a function of annealing temperature results in a red shift in the cut-off wavelength of the photodetector from 3.25 eV (381 nm) to 3.23 eV (383 nm). It is demonstrated that the sensitivity and the speed (rise/fall times) of the ZnO thin film based MSM photodetectors enhances with increasing post growth annealing temperature of ZnO thin film due to the increase in the absorption coefficient and the decrease of the total area of the grain boundaries due to the larger grain sizes formation in ZnO thin films with increasing thermal annealing temperature. DOI: 10.1088/1402-4896/ac4634
Ekip : Ümit Doğan, Fahrettin Sarcan, Karamuran Kara Koç, Furkan Kuruoğlu, Ayşe Erol - Adı : Determination of electronic band structure of quaternary ferromagnetic Ga0.97-yMn0.03CryAs epitaxial layers
Açıklama : Introducing transition metals to conventional III-V semiconductors anomalously changes their fundamental characteristics, such as electronic, magnetic, and structural properties. In this study, we show that the valence band anti-crossing (VBAC) model can be exploited to calculate the electronic band structure of the quaternary Ga0.97-xMn0.03CrxAs epitaxial layers. In this model, the localized Mn and Cr defect states interact with the valence band states (VB), reconstructing VBs and splitting each VB state. The splitting top of the VB state forms an impurity band (IB) and fundamental VB edge. Photomodulated reflectance (PR) spectroscopy is exploited to determine optical transition energies at room temperature. PR spectra were analyzed with the third derivative functional form (TDFF) signal's line shape. The experimental optical transition energies, including band-to-band and spin split-off band transitions, match the calculated optical transition energies by the VBAC model. In the calculation, the interaction energy between localized Mn/Cr-energy level and valence band edges is experimentally determined as 0.7 eV. DOI:10.1016/j.physb.2023.415074
Ekip : Omer Donmez, Mustafa Gunes, Mohamed Henini and Ayse Erol - Adı : Selective Antimicrobial Properties of W-Ge Nanocomposite Thin Films
Açıklama : The antimicrobial properties of W-Ge nanocomposite thin films as a function of Ge concentration were investigated within the scope of this study. The films were deposited on an AZ61Mg substrate using a magnetron sputter source with a co-deposition technique. Structural analyses showed that all coatings had a composite crystal structure. Additionally, the morphological investigation indicated that films had goosefoot-type structures at low Ge concentrations (5% and 10%), while Ge-rich films (40% and 60%) had cauliflower-type structures. The 20% Ge concentration coating had both structures. Regarding the surface morphology, the root mean square roughness of the surface reached its maximum value at a Ge concentration of 60% while the surface roughness and wettability of all the films showed an opposite trend. The antimicrobial activity of the W-Ge nanocomposite films against gram-negative (Salmonella typhimurium NRRLE 4413, Escherichia coli ATCC 25922) and gram- positive (Staphylococcus aureus 6538 P., Bacillus subtilis IM 622) bacteria was investigated via disc diffusion antibiotic sensitivity assay. Based on the antibacterial activity test, it was concluded that although all the films had antimicrobial efficiency against gram-negative and gram-positive bacteria, they were more effective against gram-positive bacteria. Moreover, with the increased surface roughness of the films, the number of grain boundaries, which cause an increase in the intensity of the oxide phases of the metals, increases, resulting in better antibacterial activity. DOI:10.26650/PAR.2023.00005
Ekip : Selçuk Atasoy, Yasin Kurul, Sıtkı Aktaş, Fahrettin Sarcan, Mustafa Şükrü Kurt, Adnan Ayna, Ekrem Darendelioğlu, Ayşe Erol - Adı : Fabrication of CdS nanospheresbased hybrid solar cells having increased efficiency
Açıklama : The impact of surface modification through diverse dyes (Eosin-Y, D205, N719 and N3) on structural, morphological, optical, and electrical properties of CdS/P3HT hybrid solar cells is studied. X-ray diffraction (XRD) pattern shows that CdS nanospheres have a hexagonal structure with a preferential orientation of (002) with respect to indium tin oxide (ITO) coated glass slide. Scanning electron microscopy (SEM) results indicate that compact and dense spherical morphologies of CdS occurred, and the P3HT layer also consisted of small spherical grains. The bandgap of CdS is found to be 2.52 eV according to Tauc’s plot analysis. Absorption spectra demonstrate that interfacial modification via each dye leads to an increase in the absorption in the wavelength range of 300–1000 nm. DOI: 10.1007/s00339-022-05317-2
Ekip : S. Yılmaz, A. Ünverdi, M. Tomakin, İ. Polat, E. Bacaksız - Adı : Understanding the impact of heavy ions and tailoring the optical properties of large-area monolayer WS2 using focused ion
beam
Açıklama : 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. DOI:10.1038/s41699-023-00386-0
Ekip : Fahrettin Sarcan, Nicola J. Fairbairn, Panaiot Zotev, Toby Severs-Millard, Daniel J. Gillard, Xiaochen Wang,, Ben Conran, Michael Heuken, Ayse Erol, Alexander I. Tartakovskii, Thomas F. Krauss, Gordon J. Hedley and Yue Wang - Adı : Comprehensively analysis of hot electron transport in as-grown and thermally annealed n-type modulation-doped
Al0.15Ga0.85As/GaAs0.96Bi0.4 quantum well structure
Açıklama : We report experimental and analytical results on hot electron transport in as-grown and thermally annealed n-type modulation- doped Al0.15Ga0.85As/GaAs0.96Bi0.4 quantum well (QW) structures at room temperature. The drift mobility of as-grown and thermally annealed samples is 2265 and 1414 cm2/Vs at a low electric field region, respectively. The lower electric field electron mobility for the thermally annealed sample is due to the increased 2D electron density following the annealing process. The drift velocity ( ) of the as-grown sample tends to saturate at 6.1 × 106 cm/s, contrary to the thermally annealed sample, for which no saturation is observed. The of the annealed sample is also lower due to the higher 2D electron density caused by annealing. Analyzing the experimental results concerning the theoretical model reveals that i) hot electron transport occurs in parallel mode due to the presence of electrons in both Al0.15Ga0.85As (barrier) and QW layers, ii) hot electrons transferred from QW to the barrier layer via so-called real space transfer (RST) mechanism is suppressed at higher electric fields even though the lower energy barrier between the barrier and QW layers, and iii) transfer of electrons from QW (-valley) to the nearest L-valley, inter- valley transfer (IVT), dominates on the hot electron transfer at higher electric fields even with a higher energy barrier. DOI:10.1016/j.mssp.2022.107227
Ekip : Omer Donmez, Mustafa Aydın, Selman Mutlu, Janne Puustinen, Joonas Hilska, Mircea Guina, Ayse Erol - Adı : Analysis of mixed optical transitions in dilute magnetic AlAs/GaAs/GaMnAs quantum wells grown on high substrate index by
molecular beam epitaxy
Açıklama : In this study, we report the influence of high-index substrate orientation on the optical properties of dilute Mn containing a single quantum well (QW) structure grown by molecular beam epitaxy (MBE). The electronic band structure of the samples is calculated with finite element methods (FEM). Photomodulated reflectance (PR) spectroscopy is employed to determine the optical transition energies at room temperature. PR experimental results are analyzed with the Third Derivative Functional Form (TDFF) signal function. TDFF fitting shows that the optical transition starts below the fundamental GaAs bandgap energy for the samples grown on (3 1 1) B and (4 1 1) B-oriented substrates. Comparing TDFF fitting and calculated optical transition energies with FEM show that the optical transition occurs in type-I and type-II as direct and indirect transitions, respectively. Type-I and -II optical transitions are addressed concerning the electronic band structure of the sample grown on oriented substrates. DOI:10.1016/j.mseb.2023.116349
Ekip : Shemshat Kerimova, Omer Donmez, Mustafa Gunes, Furkan Kuruoglu, Mustafa Aydın, Cebrail Gumus, Ayse Erol - Adı : High-Field Electron-Drift Velocity in n-Type Modulation-Doped GaAs0.96Bi0.04Quantum Well Structure
Açıklama : The drift velocity (vdrift) of electrons in an n-type modulation-doped GaAs0.96Bi0.04/Al0.15Ga0.85As quantum well (QW) structure is determined for electric fields (F) ranging from ≈0.4 to 3.58 kV cm−1. The resulting vdrift characteristic exhibited a linear increase and reached ≈6 × 106 cm s−1 at low electric fields then almost saturated with increasing electric field. The electron drift mobility is determined as 2265 cm2 Vs−1 in the regime where the drift velocity is linear with respect to the electric field. The drift velocity saturates at ≈6.1 × 106 cm s−1 at the electric fields between ≈2.7 and 3.4 kV cm−1. Saturation of the drift velocity is attributed to the transfer of the electrons from the QW layer (GaAs0.96Bi0.04) with higher electron mobility to the barrier layer (Al0.15Ga0.85As) and satellite valley L-valley with lower electron mobility, which initiates cooling of electrons via phonon scattering in the sample. DOI: 10.1002/pssr.202200204
Ekip : Mustafa Aydın, Selman Mutlu, Ayse Erol, Janne Puustinen, Joonas Hilska, Mircea Guina, and Omer Donmez - Adı : InGaAs-based Gunn light emitting diode
Açıklama : We report an n-type In0.53Ga0.47As based Gunn light emitting diode operated at around 1.6 μm. The device structure comprises of an n-type In0.53Ga0.47As epilayer with a thickness of 5 μm grown by Metal Organic Vapour Phase Epitaxy (MOVPE) on a semi-insulating InP substrate and fabricated in a planar architecture with a stepped structure at anode side to suppress the destructive effect of high built-in electric field in propagating Gunn domain. Gunn diode is operated under pulsed voltage with a pulse width of 60 ns and pulse duration of 4.5 ns to keep the duty cycle as low as 0.0013%. The Gunn oscillations with an 1 ns period are observed at around 4.1 kV/cm, which corresponds to the electric field threshold of Negative Differential Resistance (NDR). The light emission at around 1.6 μm also starts at the threshold electric field of the NDR region (E = 4.2 kV/cm) of the current-voltage curve, and the emission intensity increases drastically with increasing applied electric field. The observed light emission at NDR threshold electric field where Gunn oscillations appear on the voltage pulse is attributed to the impact ionisation process occurring in the current domains along the sample, which generates excess carriers to initiate the band-to-band recombination in In0.53Ga0.47As. DOI:10.1016/j.mssp.2023.107389
Ekip : G. Kalyon, S. Mutlu, F. Kuruoglu, I. Pertikel, I. Demir, A. Erol - Adı : Determination of band tail widths in MOCVD grown InGaN single layer within GaN based p-i-n LED structure through photo-
induced measurements
Açıklama : Within a p-i-n LED structure, energy band gaps of MOCVD grown %10 In content InGaN and GaN layers were obtained through traditional UV–Visible transmission-absorption measurements and utilizing surface photovoltage (SPV) and spectral photoconductivity (SPC) measurements. Moreover, all applied techniques determined that the total band offset between InGaN and GaN layers were around 0.3–0.4 eV. Furthermore, the temperature dependence of band gaps of each InGaN and GaN layer was analyzed through a modified Varshni relation where both Varshni coefficients and band tail energy width were explored. Band tails in a modified Varshni relation, SPV and SPC measurements were in agreement with each other and originated Franz-Keldysh Effect attributed to the presence of photon assisted tunneling. DOI:10.1016/j.jlumin.2022.119543
Ekip : Orhan Özdemir, Kutsal Bozkurt, Neslihan Ayarcı Kuruoğlu, Hanife Baş, Fahrettin Sarcan, Ayşe Erol, Bandar Alshehri, Karim Dogheche, Elhadj Dogheche - Adı : Dielectric Response and Capacitance Measurements of Ag/ PVAc-Si /p- Si Structure
Açıklama : In this study, the efect of Poly(vinyl acetate) latex with Silicone surfactant (shortly PVAc-Si) thin flm on the dielectric and capacitance-voltage properties of Ag / PVAc-Si /p-Si (MIS) structure were investigated. The dielectric characterization was obtained by impedance spectroscopy technique between 40 Hz-110 MHz at room temperature. The capacitance-voltage measurements were performed to clarify the fat band voltage of the sample. The frequency dependence of the real and imaginary parts of the complex impedance function indicated a space charge polarization. The Nyquist plots confrmed a single Debye type relaxation. The real and imaginary components of the complex dielectric function implied the efect of the grain and grain boundary efects in the material. Alternative current (ac) conductivity versus frequency curve of the structures displayed two diferent conductivity regimes. Nearly dc conductivity for the low frequencies and the dispersive region of the high-frequency band was obtained. The increase in ac conductivity with increasing frequency has been explained in the context of the Quantum Mechanical Tunneling (QMT) mechanism for PVAc-Si flm-induced devices. According to the capacitance-voltage measurement, it is also shown that there is a hysteresis for fat band capacitance in between the applied forward and reverse voltage. Reduction of this hysteresis is achieved by the applied voltage across terminals of the PVAcSi flm-induced MIS structure. This controllable reduction in hysteresis may fnd a place in an application for foating gate memory devices. This study also provides to understand the efect of insulator layer thickness on the dielectric behavior of MIS devices. DOI:10.1007/s12633-022-01758-9
Ekip : Banu Süngü Mısırlıoğlu · Duygu Gülşen · Furkan Kuruoğlu · Murat Çalışkan · Ayfer Sarac Ozkan · Merih Serin - Adı : Relation between thermal quenching of photoluminescence and negative capacitance on InGaN/GaN multiple quantum wells in
p-i-n structure
Açıklama : Temperature-dependent photoluminescence (PL) and surface photovoltage (SPV) measurements were carried out to detect radiative and non-radiative transitions on InGaN/GaN quantum well (QW) blue light-emitting device (LED). The emissions, peaking at 3.03 eV and 2.89 eV, were present in both PL and SPV spectrum and shifted with the temperature in a decrease- increase-decrease manner; the so-called S-shaped behavior between 30-150 K. Remarkably, the shift continued with an increase in energy (blue shift) and finally saturated for a temperature above 150 K. The first variation below 150 K was explained by the composition fluctuation of In atom in the InGaN MQW layer. In contrast, the second significant shift in peak energy was caused to the localization effect, around 60 meV. The degree of localized (σ) value agreed with the activation energy of thermal quenching of PL intensity. A strong localization effect was also attributed to the sub-bandgap trap level in the quantum well and originated negative capacitance in admittance spectroscopy measurement. DOI:10.1016/j.jlumin.2023.119749
Ekip : Orhan Özdemir, Hanife Baş, Neslihan Ayarcı Kuruoğlu, Kutsal Bozkurt, Mustafa Aydın, Fahrettin Sarcan, Ayşe Erol, Bandar Alshehri, Karim Dogheche, Elhadj Dogheche - Adı : A novel NiO-based p-i-n ultraviolet photodiode
Açıklama : In this study, the electrical and optical properties of a novel NiO-based homojunction p-i-n photodiode are reported. The p-i-n diode structure consists of Mg-doped, intrinsic and Cu-doped NiO from the top to the bottom layers, respectively. The photodiode structure was grown on a 0.7 % Nb-doped SrTiO3 (001) substrate using molecular beam epitaxy. The homojunction p-type NiO:Mg/i-NiO/n-type NiO:Cu exhibits diode characteristics. The ideality factor and barrier height of the diode are found to be 1.26 and 0.66 eV, respectively. The photoconductive properties of the photodiode were investigated by operating the diode under reverse bias, and spectral excitation of a Xe lamp. The responsivity of the photodiode is determined to be 295 mA/W at 3.9 eV. A constant photoresponse of the p-i-n photodiode between 3.75 eV and 6 eV with a responsivity of 250 mA/W is observed. DOI:10.1016/j.jallcom.2022.167806
Ekip : Fahrettin Sarcan, Umit Doğan, Ahmad Althumali, Hari B. Vasili b, Leonardo Lari, Adam Kerrigan, Furkan Kuruoğlu, Vlado K. Lazarov, Ayşe Erol - Adı : A novel hot carrier-induced blue light-emitting device
Açıklama : 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. DOI:10.1016/j.jallcom.2021.160511
Ekip : S. Mutlu, A. Erol, E. Arslan, E. Ozbay, S.B. Lisesivdin , E. Tiras - Adı : PREVENTIVE EFFECTS OF MATRIX-METALLOPROTEINASE INHIBITORS ON DENTAL EROSION
Açıklama : The purpose of this study was to investigate the effects of Chlorhexidine (CHX) and Epigallocatechin-3-gallate (EGCG) on dental erosion. Forty-four non-carious, recently extracted human third molars were used. The 44 dental crown slabs were randomly divided into 4 groups as follows: Group 1: 1.100 ppm Sodium Fluoride (NaF), Group 2: 0.61% EGCG, Group 3: 12% CHX, Group 4: 0.2 % CHX. Samples individually immersed in 30 mL of Coke® for 5 days, 4 times, 1 minute a day for erosive demineralization. The samples were immersed in 1.100 Sodium Fluoride (NaF), 0.61% EGCG, 12% CHX, 0.2% CHX for 4 times, 1 minute, each day for remineralization. The changes in the dental surface were evaluated by using a stylus profiler with surface roughness (Ra values). Topographic characteristics were assessed by Scanning Electron Microscope (SEM). Mann- Whitney U, Kruskal Wallis, and Wilcoxon Signed Ranks tests were used for statistical analyses. Significant decrease was observed in the remineralization measurement of Ra values in the EGCG group when compared with the demineralization values (p<0.05). SEM evaluation revealed that remineralization images of EGCG were observed more regularly than the other materials. With regard to topography; EGCG was found as successful as CHX and NAF in terms of turning demineralized areas into remineralized areas. https://www.fluorideresearch.online/epub/files/154.pdf
Ekip : Mine Koruyucu, Ceren İlisulu, Fahrettin Sarcan, Furkan Kuruoglu, Ayşe Erol, Figen Seymen - Adı : A quantitative analysis of electronic transport in n- and p-type modulation-doped GaAsBi/AlGaAs quantum well structures
Açıklama : 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. DOI:10.1088/1361- 6641/ac2af0
Ekip : Omer Donmez, Ayse Erol, Çağlar Çetinkaya, Erman Çokduygulular, Mustafa Aydın, Saffettin Yıldırım, Janne Puustinen, Joonas Hilska and Mircea Guina - Adı : Temperature-dependent sandwich and in-plane optical characterization of ternary chalcogenide TlSbS2
Açıklama : 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 from the analyses of its temperature-dependent photoconductivity spectra. DOI:10.1016/j.mseb.2021.115322
Ekip : Fahrettin Sarcan, Mustafa Aydin, Furkan Kuruoğlu, Omer Donmez, Saffettin Yildirim, Ayşe Erol - Adı : Improved performance of CdS powder-based hybrid solar cells through surface modification
Açıklama : The effects of surface modification of CdS through organic Eosin-Y, indoline D205, and Ru-based complex N719 and N3 dyes on CdS-based hybrid solar cells were studied. Chemical bath deposition (CBD) and doctor blade methods were in turn employed to fabricate the CdS specimens on Indium-Tin Oxide (ITO) covered glass substrates. P3HT material with and without dye coatings was covered through a spin-coater on the surface of CdS specimens. Ag paste was then deposited on the surface of P3HT to obtain hybrid solar cells. Structural analysis indicated that CdS powders showed a cubic growth with the preferred orientation of (111). Morphological analysis demonstrated that CdS powders exhibited hierarchical morphology and the morphology turned to granular structure with some porosity upon deposition of both N3 dye and P3HT layers. Absorption plots indicated that Eosin-Y dye loading led to a rise in the absorbance values of CdS specimens. After dye loading, photoluminescence data of CdS-based heterostructure illustrated a decrement in the luminescence intensity, implying that effective exciton dissociation was obtained. Current density-voltage (J-V) characteristics of the hybrid solar cells depicted that the best overall efficiency was observed for Eosin-Y-modified cell as 0.135%. This proved that surface modification by Eosin-Y dye led to a better interfacial contact between CdS and P3HT bilayer due to the enhancement in the charge separation. DOI:10.17714/gumusfenbil.893925
Ekip : Salih YILMAZ,Ahmet ÜNVERDİ, Murat TOMAKİN, İsmail POLAT, Emin BACAKSIZ - Adı : Determination of band tail widths in MOCVD grown InGaN single layer within GaN based p-i-n LED structure through photo-
induced measurements
Açıklama : Within a p-i-n LED structure, energy band gaps of MOCVD grown %10 In content InGaN and GaN layers were obtained through traditional UV–Visible transmission-absorption measurements and utilizing surface photovoltage (SPV) and spectral photoconductivity (SPC) measurements. Moreover, all applied techniques determined that the total band offset between InGaN and GaN layers were around 0.3–0.4 eV. Furthermore, the temperature dependence of band gaps of each InGaN and GaN layer was analyzed through a modified Varshni relation where both Varshni coefficients and band tail energy width were explored. Band tails in a modified Varshni relation, SPV and SPC measurements were in agreement with each other and originated Franz-Keldysh Effect attributed to the presence of photon assisted tunneling. DOI: 10.1016/j.jlumin.2022.119543
Ekip : Orhan Özdemir, Kutsal Bozkurt, Neslihan Ayarcı Kuruoğlu,Hanife Baş ,Fahrettin Sarcan, Ayşe Erol , Bandar Alshehri , Karim Dogheche , Elhadj Dogheche - Adı : Electronic transport in n-type modulation-doped AlGaAs/GaAsBi quantum well structures: influence of Bi and thermal annealing
on electron effective mass and electron mobility
Açıklama : 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 °C and 350 °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 °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 °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 °C for 60 s) Bi-containing QWs and two electron subbands (e1 and e2) for the annealed (at 350 °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. DOI 10.1088/1361-6641/ab5d8d
Ekip : Ömer Dönmez, Mustafa Aydın, Şükrü Ardalı, Saffettin Yıldırım, Engin Tıraş, Ferhat Nutku, Çağlar Çetinkaya, Erman Çokduygulular, J. Puustinen, J. Hilska - Adı : Photoluminescence characteristic of as-grown and thermally annealed n- and p-type modulation-doped Ga0.68In0.32NxAs1-
x/GaAs quantum well structures
Açıklama : The electronic band structure of n- and p-type modulation-doped Ga0.68In0.32NyAs1-y/GaAs (y=0, 0.9, 1.2, 1.7) quantum well is calculated using the 10 band k•p model and the finite element method for valance band (VB) and band anti-crossing model for conduction band. Experimental characterization has been carried out temperature dependent photoluminescence (PL) measurements at room temperature. It is determined that optical transition occurs between the first quantized energy level in the conduction band (CB) and VB for n-type samples. While it occurs between localized level and VB, due to empty of the localized level closes CB for p-type samples. It is observed that the intensity of PL emission is higher for p-type samples and the effective bandgap energy redshifts with increasing Nitrogen (N) concentration. Rapid thermal annealing improves the optical quality and causes a blueshift effect. We have determined a similar amount of the blueshift for n-type N-free and N-containing samples, which may be the interdiffusion of the In/Ga atoms. The temperature dependency of the bandgap energies has been fitted using a semi-empirical Varshni equation. It has been observed that thermal Debye temperature and thermal expansion coefficient decreases with N. The redshift of the temperature dependence of the bandgap becomes larger as N concentration decreases. On the other hand, the annealing process causes a reduction in the temperature dependency of the bandgap for p-type samples. DOI: 10.1016/j.tsf.2021.138785
Ekip : Omer Donmez, Fahrettin Sarcan, Ayse Erol, Fatih Ungan, Hüseyin Sarı - Adı : Improvement of fill factor by the utilization of Zn-doped PEDOT:PSS hole-transport layers for p-i-n planar type of perovskite solar
cells
Açıklama : 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. DOI:10.1016/j.electacta.2021.138658
Ekip : Hamed Moeini Alishah , Fatma Pinar Gokdemir Choi , Furkan Kuruoglu , Ayse Erol , Serap Gunes - Adı : Dilute nitride resonantcavity light emitting diode
Açıklama : 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. DOI: 10.1016/j.optlastec.2019.105888
Ekip : Fahrettin Sarcan, Yue Wang, Thomas F. Krauss, Tülin Eruçar, Ayşe Erol - Adı : Determination of the acoustic phonon-hot carriers interaction in n- and p-type modulation-doped GaInNAs/GaAs quantum wells
Açıklama : 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. DOI:10.1016/j.physb.2021.412946
Ekip : Ömer Dönmez, Fahrettin Sarcan, Ayşe Erol
| Adı | Açıklama | Ekip |
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| Ultraviyole Işınım Algılamaya Yönelik "Solar Blind" Yarıiletken Sensör Geliştirilmesi | Bu proje, Nero Savunma Sanayi A.Ş. ile ortaklaşa yürütülen bir projedir. Alevin DUV (Derin Ultraviyole) karakteristik emisyonunu algılayan bir sensör üretmeyi hedefliyoruz. Prototip sensör, Prof. Dr. Ayşe Erol ve Doç. Dr. Fahrettin Sarcan tarafından tasarlandı, üretildi ve test edildi. Prototip, Teknoloji Hazırlık Seviyesi 3 (THS 3) düzeyindedir. | Nero Endüstri (Proje Partneri), Prof. Dr. Ayşe Erol (Yürütücü), Doç. Dr. Fahrettin Sarcan (Yürütücü), Ümit Doğan (Araştırmacı) |
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| Optik olarak ölçüm yapan bir manyetik alan ölçüm cihazı | Düşük manyetik alan değerlerini ölçen aygıt | Prof.Dr. Ömer Dönmez, Prof.Dr. Ayşe Erol |
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| Proje (BAP) | Tez Projesi:BİZMUT İÇEREN III-V GRUBU YARIİLETKENLERDE ELEKTRONİK TRANSPORT MEKANİZMALARININ İNCELENMESİ | Optimum büyütme şartlarında büyütülen örneklerin karakterizasyonu | Prof.Dr. Ömer Dönmez (yürütücü), Dr. Mustafa Aydın |
| Proje (BAP) | Modülasyon katkılı GaBiAs kuantum kuyulu yapıların optik ve elektrik transport özelliklerinin incelenmesi | Örgü uyumsuz alaşımların elektronik bant yapı düzenlemesi ve optoelektronik uygulama potansiyellerinin belirlenmesi | Prof.Dr. Ömer Dönmez (yürütücü), Prof.Dr. Ayşe Erol, Dr. Öğr. Üyes, Saffettin Yıldırım, Prof.Dr. Elif Akalın, Doç.Dr. Barış Kınacı, Dr.Öğr. Kamuran Kara, Doç.Dr. Fahrettin Sarcan, Prof.Dr. Ferhat Nutku |
| Proje (BAP) | Katkılı GaAsBi/GaAs epilayer yapısının transport özelliklerinin incelenmesi | Örgü uyumsuz alaşımların transport özelliklerinin belirlenmesi amaçlanmıştır | Prof.Dr. ömer Dönmez (Proje Yürütücüsü),Dr.Öğr. Üyesi Saffettin Yıldırım;Dr.Öğr. Üyesi Mustafa Aydın, Prof.Dr. Ayşe Erol |
| Proje (TÜBİTAK) | Seyreltik Bizmut Modülasyonu Katkılı GaAsBi/GaAs Kuantum Kuyusu Yapılarında Bizmut Konsantrasyonunun Elektronik Transport Özelliklerine Etkisi | Bu projede, Biszut'un n- ve p- modülasyonlu katkılanmış kuantum kuyu yapıları üzerindeki optik ve elektronik transport üzerindeki etkileri, çeşitli bizmut konsantrasyonlarıyla incelenecektir. Kullanılacak örnekler, proje ekibi tarafından tasarlandı ve bunlar Tampere Teknik Üniversitesi, Finlandiya'da büyütüldü. Optik özellikler, Fotolüminesans ve Foto-modüle Edilmiş Yansıma teknikleri kullanılarak incelenirken, elektronik taşıma mekanizmalarını belirlemek için Hall Etkisi ve manyetotransport ölçümleri gerçekleştirilecektir. Ayrıca, elektron ve boşlukların satürasyon hızlarını belirlemek ve NDR etkisinin varlığında yüksek hızlı I-V ölçümleri yapılacaktır. | Prof Dr. Ömer Dönmez(Yürütücü), Prof. Dr. Ayşe Erol (Araştırmacı), Saffettin Yıldırım (Araştırmacı), Ferhat Nutku (Araşırmacı), Mehmet Çetin Arıkan (Danışman) |
| Proje (BAP) | Uyumsuz Yarıiletken Alaşımların Optoelektronik Davranışlarının İncelenmesi. | Bu projenin amacı, farklı bizmut bileşimine sahip ve farklı büyütme koşullarında büyütülmüş olan külçe ve GaAsBi/GaAs kuantum kuyusu yapılarının optik özelliklerinin ve bu yapılardaki elektronik transport mekanizmalarının incelenmesi ve elde edilen verilerden yararlanılarak optik sinyal kalitesi ve taşıyıcı mobilitesi açısından en iyi performansa sahip olan optik haberleşmenin ? 1300nm dalgaboyunda çalışabilecek optoelektronik aygıtların geliştirilebilmesine temel olabilecek en uygun örnek yapısının belirlenmesidir. | Prof. Dr. Ayşe Erol ve Yard. Doç. Dr. Saffetin Yıldırım Prof. Dr. Deniz Değer Ulutaş, Araş. Gör. Şahin Yakut |
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