Browsing by Author "Arslan, E."

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Open Access
21.2 mV/K high-performance Ni(50 nm)-Au(100 nm)/Ga2O3/p-Si vertical MOS type diode and the temperature sensing characteristics with a novel drive mode
(Institute of Electrical and Electronics Engineers, 2022-11-09) Çiçek, O.; Arslan, E.; Altındal, Ş.; Badali, Y.; Özbay, Ekmel
Sensitivity ( S ) and drive mode are crucial issues for the vertical metal-oxide-semiconductor (MOS) type diode applied in temperature sensing. In this study, experimentally, we indicated that the S values of the Ni(50 nm) - Au(100 nm) /Ga2O3/ p -Si vertical MOS type diode, using the measured capacitance–voltage ( Cm – V ) outputs, are obtained with a novel drive mode. We applied the constant capacitance mode to drive the silicon thermo-diodes as well as constant current mode, and constant voltage mode, which are known as two different methods in the literature. Meanwhile, the S value is 21.2 mV/K at 1 nF. This value is the highest value proven in the literature excepting the cryogenic temperature region, and near room temperature. This study provided an original structure for the silicon thermo-diodes and a novel way to drive them.
Open Access
Buffer effects on the mosaic structure of the HR-GaN grown on 6H-SiC substrate by MOCVD
(Springer New York LLC, 2017) Arslan, E.; Öztürk, M. K.; Tıraş, E.; Tıraş, T.; Özçelik, S.; Özbay, Ekmel
High-resistive GaN (>108 Ω cm) layers have been grown with different buffer structures on 6H-SiC substrate using metalorganic chemical vapor deposition reactor. Different combination of the GaN/AlN super lattice, low temperature AlN, high temperature AlN and AlxGa1−xN (x ≈ 0.67) layers were used in the buffer structures. The growth parameters of the buffer layers were optimized for obtaining a high-resistive GaN epilayer. The mosaic structure parameters, such as lateral and vertical coherence lengths, tilt and twist angle (and heterogeneous strain), and dislocation densities (edge and screw dislocations) of the high-resistive GaN epilayers have been investigated using x-ray diffraction measurements. In addition, the residual stress behaviors in the high-resistive GaN epilayers were determined using both x-ray diffraction and Raman measurements. It was found that the buffer structures between the HR-GaN and SiC substrate have been found to have significant effect on the surface morphology and the mosaic structures parameters. On the other hand, both XRD and Raman results confirmed that there is low residual stress in the high-resistive GaN epilayers grown on different buffer structures.
Open Access
Buffer optimization for crack-free GaN epitaxial layers grown on Si(111) substrate by MOCVD
(Institute of Physics Publishing Ltd., 2008) Arslan, E.; Ozturk, M. K.; Teke, A.; Ozcelik, S.; Özbay, Ekmel
We report the growth of GaN films on the Si(1 1 1) substrate by metalorganic chemical vapour phase deposition (MOCVD). Different buffer layers were used to investigate their effects on the structural and optical properties of GaN layers. A series of GaN layers were grown on Si(1 1 1) with different buffer layers and buffer thicknesses and were characterized by Nomarski microscopy, atomic force microscopy, high-resolution x-ray diffraction (XRD) and photoluminescence (PL) measurements. We first discuss the optimization of the LT-AlN/HT-AlN/Si(1 1 1) templates and then the optimization of the graded AlGaN intermediate layers. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.6 νm. The XRD and PL measurements results confirmed that a wurtzite GaN was successfully grown. The resulting GaN film surfaces were flat, mirror-like and crack-free. The mosaic structure in the GaN layers was investigated. With a combination of Williamson-Hall measurements and the fitting of twist angles, it was found that the buffer thickness determines the lateral coherence length, vertical coherence length, as well as the tilt and twist of the mosaic blocks in GaN films. The PL spectra at 8 K show that a strong band edge photoluminescence of GaN on Si (1 1 1) emits light at an energy of 3.449 eV with a full width at half maximum (FWHM) of approximately 16 meV. At room temperature, the peak position and FWHM of this emission become 3.390 eV and 58 meV, respectively. The origin of this peak was attributed to the neutral donor bound exciton. It was found that the optimized total thickness of the AlN and graded AlGaN layers played a very important role in the improvement of quality and in turn reduced the cracks during the growth of GaN/Si(1 1 1) epitaxial layers.
Open Access
Chondrogenic differentiation of mesenchymal stem cells on glycosaminoglycan-mimetic peptide nanofibers
(American Chemical Society, 2016) Yaylaci, S .U.; Sen, M.; Bulut, O.; Arslan, E.; Güler, Mustafa O.; Tekinay, A. B.
Glycosaminoglycans (GAGs) are important extracellular matrix components of cartilage tissue and provide biological signals to stem cells and chondrocytes for development and functional regeneration of cartilage. Among their many functions, particularly sulfated glycosaminoglycans bind to growth factors and enhance their functionality through enabling growth factor-receptor interactions. Growth factor binding ability of the native sulfated glycosaminoglycans can be incorporated into the synthetic scaffold matrix through functionalization with specific chemical moieties. In this study, we used peptide amphiphile nanofibers functionalized with the chemical groups of native glycosaminoglycan molecules such as sulfonate, carboxylate and hydroxyl to induce the chondrogenic differentiation of rat mesenchymal stem cells (MSCs). The MSCs cultured on GAG-mimetic peptide nanofibers formed cartilage-like nodules and deposited cartilage-specific matrix components by day 7, suggesting that the GAG-mimetic peptide nanofibers effectively facilitated their commitment into the chondrogenic lineage. Interestingly, the chondrogenic differentiation degree was manipulated with the sulfonation degree of the nanofiber system. The GAG-mimetic peptide nanofibers network presented here serve as a tailorable bioactive and bioinductive platform for stem-cell-based cartilage regeneration studies.
Open Access
Comparison of the transport properties of high quality AlGaN/AlN/GaN and AllnN/AlN/GaN two-dimensional electron gas heterostructures
(AIP Publishing LLC, 2009-01-07) Tülek, R.; Ilgaz, A.; Gökden, S.; Teke, A.; Öztürk, M. K.; Kasap, M.; Özçelik, S.; Arslan, E.; Özbay, Ekmel
The transport properties of high mobility AlGaN/AlN/GaN and high sheet electron density AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures were studied. The samples were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The room temperature electron mobility was measured as 1700 cm(2)/V s along with 8.44 X 10(12) cm(-2) electron density, which resulted in a two-dimensional sheet resistance of 435 Omega/square for the Al(0.2)Ga(0.8)N/AlN/GaN heterostructure. The sample designed with an Al(0.88)In(0.12)N barrier exhibited very high sheet electron density of 4.23 X 10(13) cm(-2) with a corresponding electron mobility of 812 cm(2)/V s at room temperature. A record two-dimensional sheet resistance of 182 Omega/square was obtained in the respective sample. In order to understand the observed transport properties, various scattering mechanisms such as acoustic and optical phonons, interface roughness, and alloy disordering were included in the theoretical model that was applied to the temperature dependent mobility data. It was found that the interface roughness scattering in turn reduces the room temperature mobility of the Al(0.88)In(0.12)N/AlN/GaN heterostructure. The observed high 2DEG density was attributed to the larger polarization fields that exist in the sample with an Al0.88In0.12N barrier layer. From these analyses, it can be argued that the AlInN/AlN/GaN high electron mobility transistors (HEMTs), after further optimization of the growth and design parameters, could show better transistor performance compared to AlGaN/AlN/GaN based HEMTs. c 2009 American Institute of Physics.
Open Access
Complementary and alternative technique for the determination of electron effective mass: Quantum hall effect
(Taylor & Francis Inc., 2016) Ardalı, S.; Tiras, E.; Arslan, E.; Özbay, Ekmel
The quantum Hall effect measurements in the AlInN/AlN/GaN heterostructure are studied in the temperature range from 1.8 K to 14 K and a magnetic field up to 11 T. The quantized two-dimensional electron gas was placed at the AlN/GaN interface. The Hall resistance of two-dimensional electron gas has been found to be quantized at multiple integers of von Klitzing constant that refers to the integer quantum Hall effect. The experimental data have been used to determine the Fermi energy, carrier density, and effective mass two-dimensional electrons. The results are in agreement with those derived from the longitudinal magnetoresistance in the same structure.
Open Access
Current transport mechanisms and trap state investigations in (Ni/Au)-AlN/GaN Schottky barrier diodes
(Elsevier, 2010-10-13) Arslan, E.; Bütün, S.; Şafak, Y.; Çakmak, H.; Yu, H.; Özbay, Ekmel
The current transport mechanisms in (Ni/Au)-AlN/GaN Schottky barrier diodes (SBDs) were investigated by the use of current-voltage characteristics in the temperature range of 80-380 K. In order to determine the true current transport mechanisms for (Ni/Au)-AlN/GaN SBDs, by taking the Js(tunnel), E 0, and Rs as adjustable fit parameters, the experimental J-V data were fitted to the analytical expressions given for the current transport mechanisms in a wide range of applied biases and at different temperatures. Fitting results show the weak temperature dependent behavior in the saturation current and the temperature independent behavior of the tunneling parameters in this temperature range. Therefore, it has been concluded that the mechanism of charge transport in (Ni/Au)-AlN/GaN SBDs, along the dislocations intersecting the space charge region, is performed by tunneling. In addition, in order to analyze the trapping effects in (Ni/Au)-AlN/GaN SBDs, the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics were measured in the frequency range 0.7-50 kHz. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming the models in which traps are located at the heterojunction interface. The density (Dt) and time constants (τt) of the trap states have been determined as a function of energy separation from the conduction-band edge (Ec - Et) as Dt≅ (5-8)×10 12eV-1 cm-2andτt≅(43-102) μs, respectively.
Open Access
Current-Transport mechanisms in the AlInN/AlN/GaN single-channel and AlInN/AlN/GaN/AlN/GaN double-channel heterostructures
(Elsevier, 2013) Arslan, E.; Turan, S.; Gökden, S.; Teke, A.; Özbay, Ekmel
Current-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single channel (SC) and AlInN/AlN/GaN/AlN/GaN double channel (DC) heterostructures. A simple model was adapted to the current-transport mechanisms in DC heterostructure. In this model, two Schottky diodes are in series: one is a metal-semiconductor barrier layer (AIInN) Schottky diode and the other is an equivalent Schottky diode, which is due to the heterojunction between the AlN and GaN layer. Capacitance-voltage studies show the formation of a two-dimensional electron gas at the AlN/GaN interface in the SC and the first AlN/GaN interface from the substrate direction in the DC. In order to determine the current mechanisms for SC and DC heterostructures, we fit the analytical expressions given for the tunneling current to the experimental current-voltage data over a wide range of applied biases as well as at different temperatures. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. At both a low and medium forward-bias voltage values for Schottky contacts on AlInN/AlN/GaN/AlN/GaN DC and AlInN/AlN/GaN SC heterostructures, the data are consistent with electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-420 K.
Open Access
Discolation-governed current-transport mechanism in (Ni/Au)-AlGaN/AIN/GaN heterostructures
(A I P Publishing LLC, 2009-01-22) Arslan, E.; Altındal, S.; Özçelik, S.; Özbay, Ekmel
The current-transport mechanisms in (Ni/Au)-Al(0,22)Ga(0,78)N/AlN/GaN heterostructures were studied by using temperature dependent forward-bias current-voltage (I-V) characteristics in the temperature range of 80-410 K. In order to determine the current mechanisms for (Ni/Au)-Al(0,22)Ga(0,78)N/AlN/GaN heterostructures, we fitted the experimental I-V data to the analytical expressions given for the current-transport mechanisms in a wide range of applied biases and at different temperatures. The contributions of thermionic-emission, generation-recombination, tunneling, leakage currents that are caused by inhomogeneities, and defects at the metal-semiconductor interface current mechanisms were all taken into account. The best fitting results were obtained for the tunneling current mechanism. On the other hand, we did not observe sufficient agreement between the experimental data and the other current mechanisms. The temperature dependencies of the tunneling saturation current (I(t)) and tunneling parameters (E(0)) were obtained from fitting results. We observed a weak temperature dependence of the saturation current and the absence of the temperature dependence of the tunneling parameters in this temperature range. The results indicate that in the temperature range of 80-410 K, the mechanism of charge transport in the (Ni/Au)-Al(0.22)Ga(0.78)N/AlN/GaN heterostructure is performed by tunneling among those dislocations intersecting the space charge region. The dislocation density (D) that was calculated from the I-V characteristics, according to a model of tunneling along the dislocation line, gives the value of 0.24x10(7) cm(-2). This value is close in magnitude to the dislocation density that was obtained from the x-ray diffraction measurements.
Open Access
Double subband occupation of the two-dimensional electron gas in InxAl1-XN/AlN/GaN/AlN heterostructures with a low indium content (0.064 ≤ x ≤ 0.140) barrier
(Elsevier, 2010-05-08) Lisesivdin, S. B.; Tasli, P.; Kasap, M.; Ozturk, M.; Arslan, E.; Ozcelik, S.; Özbay, Ekmel
We present a carrier transport study on low indium content (0.064 ≤ x ≤ 0.140) InxAl1 - xN/AlN/GaN/AlN heterostructures. Experimental Hall data were carried out as a function of temperature (33-300 K) and a magnetic field (0-1.4 T). A two-dimensional electron gas (2DEG) with single or double subbands and a two-dimensional hole gas were extracted after implementing quantitative mobility spectrum analysis on the magnetic field dependent Hall data. The mobility of the lowest subband of 2DEG was found to be lower than the mobility of the second subband. This behavior is explained by way of interface related scattering mechanisms, and the results are supported with a one-dimensional self-consistent solution of non-linear Schrödinger- Poisson equations.
Open Access
The effect of GaN thickness inserted between two AlN layers on the transport properties of a lattice matched AlInN/AlN/GaN/AlN/GaN double channel heterostructure
(Elsevier BV, 2014-01-31) Tülek, R.; Arslan, E.; Bayraklı, A.; Turhan, S.; Gökden, S.; Duygulu, Ö.; Kaya, A.; Fırat, T.; Teke, A.; Özbay, Ekmel
One AlInN/AlN/GaN single channel heterostructure sample and four AlInN/AlN/GaN/AlN/GaN double channel heterostructure samples with different values of the second GaN layer were studied. The interface profiles, crystalline qualities, surface morphologies, and dislocation densities of the samples were investigated using high resolution transmission electron microscopy, atomic force microscopy, and high-resolution X-ray diffraction. Some of the data provided by these measurements were used as input parameters in the calculation of the scattering mechanisms that govern the transport properties of the studied samples. Experimental transport data were obtained using temperature dependent Hall effect measurements (10-300 K) at low (0.5 T) and high (8 T) magnetic fields to exclude the bulk transport from the two-dimensional one. The effect of the thickness of the second GaN layer inserted between two AlN barrier layers on mobility and carrier concentrations was analyzed and the dominant scattering mechanisms in the low and high temperature regimes were determined. It was found that Hall mobility increases as the thickness of GaN increases until 5 nm at a low temperature where interface roughness scattering is observed as one of the dominant scattering mechanisms. When GaN thicknesses exceed 5 nm, Hall mobility tends to decrease again due to the population of the second channel in which the interface becomes worse compared to the other one. From these analyses, 5 nm GaN layer thicknesses were found to be the optimum thicknesses required for high electron mobility. (C) 2013 Published by Elsevier B.V.
Open Access
The effect of Si(x)N(y) interlayer on the quality of GaN epitaxial layers grown on Si(111) substrates by MOCVD
(ELSEVIER, 2008-04-27) Arslan, E.; Ozturk, M. K.; Ozcelik, S.; Özbay, Ekmel
In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(111) substrates by metal-organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(111) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(111) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 mu m. Secondly, the effect of in situ substrate nitridation and the insertion of an Si(x)N(y) intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the Si(x)N(y) layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without Si(x)N(y) layer) and B (with Si(x)N(y) layer on Si(111)). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0002) diffraction from the GaN epilayer of the sample B in omega-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a Si(x)N(y) intermediate layer significantly improved the optical and structural properties. In sample C (with Si(x)N(y) layer on Al(0.11)Ga(0.89)N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties.
Open Access
Effective mass of electron in monolayer graphene: Electron-phonon interaction
(AIP Publishing LLC, 2013-01-25) Tiras, E.; Ardali, S.; Tiras, T.; Arslan, E.; Cakmakyapan, S.; Kazar, O.; Hassan, J.; Janzén, E.; Özbay, Ekmel
Shubnikov-de Haas (SdH) and Hall effect measurements performed in a temperature range between 1.8 and 275 K, at an electric field up to 35 kV m -1 and magnetic fields up to 11 T, have been used to investigate the electronic transport properties of monolayer graphene on SiC substrate. The number of layers was determined by the use of the Raman spectroscopy. The carrier density and in-plane effective mass of electrons have been obtained from the periods and temperature dependencies of the amplitude of the SdH oscillations, respectively. The effective mass is in good agreement with the current results in the literature. The two-dimensional (2D) electron energy relaxations in monolayer graphene were also investigated experimentally. The electron temperature (Te) of hot electrons was obtained from the lattice temperature (TL) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss indicate that the energy relaxation of electrons is due to acoustic phonon emission via mixed unscreened piezoelectric interaction and deformation-potential scattering.
Open Access
Electrical characterization of MS and MIS structures on AlGaN/AlN/GaN heterostructures
(ELSEVIER, 2010) Arslan, E.; Bütün, S.; Şafak, Y.; Uslu, H.; Tascioglu I.; Altindal, S.; Özbay, Ekmel
The forward and reverse bias I-V, C-V, and G/ω-V characteristics of (Ni/Au) Schottky barrier diodes (SBDs) on the Al 0.22Ga 0.78N/AlN/GaN high-electron-mobility-transistor (HEMTs) without and with SiN x insulator layer were measured at room temperature in order to investigate the effects of the insulator layer (SiN x) on the main electrical parameters such as the ideality factor (n), zero-bias barrier height ( B0), series resistance (R s), interface-state density (N ss). The energy density distribution profiles of the N ss were obtained from the forward bias I-V characteristics by taking into account the voltage dependence of the effective barrier height ( e) and ideality factor (n V) of devices. In addition, the N ss as a function of E c-E ss was determined from the low-high frequency capacitance methods. It was found that the values of N ss and R s in SBD HEMTs decreases with increasing insulator layer thickness.
Open Access
The electrical, optical, and structural properties of GaN epitaxial layers grown on Si(111) substrate with SiNx interlayers
(ELSEVIER, 2009-10-12) Arslan, E.; Duygulu, Ö.; Kaya, A. A.; Teke, A.; Özçelik, S.; Özbay, Ekmel
The effect of the in situ substrate nitridation time on the electrical, structural and optical properties of GaN films grown on Si(111) substrates by metal organic chemical vapor deposition (MOCVD) was investigated. A thin buffer layer of silicon nitride (SiNx) with various thicknesses was achieved through the nitridation of the substrate at different nitridation times ranging from 0 to 660 s. The surface roughness of the GaN film, which was grown on the Si substrate 10 s, exhibited a root mean square (RMS) value of 1.12 nm for the surface roughness. However, further increments in the nitridation times in turn cause increments in the surface roughness in the GaN layers. The number of threading dislocation (TD) was counted from plan-view TEM (Transmission Electron Microscopy) images. The determined density of these threading dislocations was of the order of 9×109 cm-2. The sheet resistances of the GaN layers were measured. The average sheet resistance significantly increases from 2867 Ω sq-1 for sample A (without nitridation) to 8124 Ω sq-1 for sample F (with 660 s nitridation). The photoluminescence (PL) measurements of the samples nitridated at various nitridation times were done at a temperature range of 10-300 K. A strong band edge PL emission line, which was centered at approx. 3.453 eV along with its phonon replicas which was separated by approx. 92 meV in successive orders, was observed at 10 K. The full width at half maximum (FWHM) of this peak is approx. 14 meV, which indicates the reasonable optical quality of the GaN epilayers grown on Si substrate. At room temperature, the peak position and FWHM of this emission became 3.396 eV and 58 meV, respectively.
Open Access
Energy relaxation rates in AlInN/AlN/GaN heterostructures
(Springer, 2012-06-27) Tiras, E.; Ardali, S.; Arslan, E.; Özbay, Ekmel
The two-dimensional (2D) electron energy relaxation in Al0.83In0.17N/AlN/GaN heterostructures has been investigated experimentally. Shubnikov-de Haas (SdH) effect measurements were employed in the investigations. The electron temperature (T (e)) of hot electrons was obtained from the lattice temperature (T (L)) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss are also compared with current theoretical models for power loss in 2D semiconductors. The power loss from the electrons was found to be proportional to (T (e) (3) - T (L) (3) ) for electron temperatures in the range 1.8 K < T (e) < 14 K, indicating that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. The effective mass and quantum lifetime of the 2D electrons have been determined from the temperature and magnetic field dependencies of the amplitude of SdH oscillations, respectively. The values obtained for quantum lifetime suggest that remote ionized impurity scattering is the dominant scattering mechanism in Al0.83In0.17N/AlN/GaN heterostructures.
Open Access
Evolution of the mosaic structure in InGaN layer grown on a thick GaN template and sapphire substrate
(Springer, 2013-08-08) Arslan, E.; Ozturk, M. K.; Cakmak, H.; Demirel, P.; Ozcelik, S.; Özbay, Ekmel
The InxGa1-xN epitaxial layers, with indium (x) concentration changes between 0.16 and 1.00 (InN), were grown on GaN template/(0001) Al2O3 substrate by metal organic chemical vapour deposition. The indium content (x), lattice parameters and strain values in the InGaN layers were calculated from the reciprocal lattice mapping around symmetric (0002) and asymmetric (10-15) reflection of the GaN and InGaN layers. The characteristics of mosaic structures, such as lateral and vertical coherence lengths, tilt and twist angle and heterogeneous strain and dislocation densities (edge and screw dislocations) of the InGaN epilayers and GaN template layers were investigated by using high-resolution X-ray diffraction (HR-XRD) measurements. With a combination of Williamson-Hall (W-H) measurements and the fitting of twist angles, it was found that the indium content in the InGaN epilayers did not strongly effect the mosaic structures' parameters, lateral and vertical coherence lengths, tilt and twist angle, or heterogeneous strain of the InGaN epilayers.
Open Access
Extraction and scattering analyses of 2D and bulk carriers in epitaxial graphene-on-SiC structure
(Elsevier BV, 2014-09) Lisesivdin, S. B.; Atmaca, G.; Arslan, E.; Çakmakyapan S.; Kazar, Ö.; Bütün, S.; Ul-Hassan, J.; Janzén, E.; Özbay, Ekmel
Hall effect measurements of a graphene-on-SiC system were carried out as a function of temperature (1.8-200 K) at a static magnetic field (0.51) With the analysis of temperature dependent single-field Hall data with the Simple Parallel Conduction Extraction Method (SPCEM), bulk and two-dimensional (2D) carrier densities and mobilities were extracted successfully. Bulk carrier is attributed to SIC substrate and 2D carrier is attributed to the graphene layer. For each SPCEM extracted carrier data, relevant three-dimensional or 2D scattering analyses were performed. Each SPCEM extracted carrier data were explained with the related scattering analyses. A temperature independent mobility component, which may related to an interaction between graphene and SIC, was observed for both scattering analyses with the same mobility limiting value. With the SPCEM, effective ionized impurity concentration of SiC substrate, extracted 2D-mobility, and sheet carrier density of the graphene layer are calculated with using temperature dependent static magnetic field Hall data. (c) 2014 Elsevier B.V. All rights reserved.
Open Access
Forward tunneling current in Pt/p-InGaN and Pt/n-InGaN Schottky barriers in a wide temperature range
(Elsevier, 2012-07-27) Arslan, E.; Çakmak, H.; Özbay, Ekmel
The current-transport mechanisms of the Pt contacts on p-InGaN and n-InGaN were investigated in a wide temperature range (80-360 K) and in the forward bias regime. It was found that the ideality factor (n) values and Schottky barrier heights (SBHs), as determined by thermionic emission (TE), were a strong function of temperature and Φb0 show the unusual behavior of increasing linearly with an increase in temperature from 80 to 360 K for both Schottky contacts. The tunneling saturation ( JTU(0)) and tunneling parameters (E 0) were calculated for both Schottky contacts. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. The results indicate that the dominant mechanism of the charge transport across the Pt/p-InGaN and Pt/n-InGaN Schottky contacts are electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-360 K.
Open Access
Frequency and temperature dependence of the dielectric and AC electrical conductivity in (Ni/Au)/AlGaN/AlN/GaN heterostructures
(Elsevier, 2010) Arslan, E.; Şafak, Y.; Taşçioğlu, I.; Uslu, H.; Özbay, Ekmel
The dielectric properties and AC electrical conductivity (σ ac)of the (Ni/Au)/Al 0.22Ga 0.78N/AlN/GaN heterostructures, with and without the SiNx passivation, have been investigated by capacitance-voltage and conductance-voltage measurements in the wide frequency (5kHz-5 MHz) and temperature (80-400 K) range. The experimental values of the dielectric constant (ε'), dielectric loss (ε' '), loss tangent (tand), σ ac and the real and imaginary part of the electric modulus (M' and M' ') were found to be a strong function of frequency and temperature. A decrease in the values of ε' and ε' ' was observed, in which they both showed an increase in frequency and temperature. The values of M' and M' ' increase with increasing frequency and temperature. The σ ac increases with increasing frequency, while it decreases with increasing temperature. It can be concluded, therefore, that the interfacial polarization can occur more easily at low frequencies and temperatures with the number of interface states density located at the metal/semiconductor interface. It contributes to the e' and σ ac. © 2009 Elsevier B.V. All rights reserved.