Browsing by Author "Arslan, Engin"
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Item Open Access Current transport properties of (Au/Ni)/HfAlO3/n-Si metal–insulator–semiconductor junction(Elsevier Ltd, 2020-09-11) Arslan, Engin; Badali, Yosef; Aalizadeh, Majid; Altındal, Semsettin; Ozbay, EkmelIn this study, HfAlO3 ternary alloy thin film was grown on n-type silicon using the atomic layer deposition method. The current transport mechanisms in the (Au/Ni)/HfAlO3/n-Si junction were examined over a wide temperature range (80–360 K). The values obtained for the ideality factor (n) varied from 22.93 to 3.94 and the barrier height at zero bias (ФB0) ranged from 0.221 eV to 0.821 eV as the temperature changed from 80 to 360 K. The ΦB0–n and ΦB0–q/2 kT characteristics were investigated to explain the higher n values and non-ideal behavior of the Richardson curves. Two linear regions were found at low temperatures (LTs; 80–180 K) and high temperatures (HTs; 200–360 K), which indicated the presence of a Gaussian distribution barrier height and the average barrier heights (Φ‾B0) were identified. The values obtained for Φ‾Bo were 0.734 eV for LTs and 1.125 eV for HTs, and the values of σs were 0.085 V for LTs and 0.140 V for HTs. The values obtained for Nss decreased as the temperature increased and they varied between ~1012 and 1013 eV−1 cm−2. Finally, the dielectric behavior and conductivity of the (Au/Ni)/HfAlO3/n-Si junction were investigated at frequencies between 5 kHz and 2 MHz at room temperature. The values determined for ε′ and ε′′ at −1 V and 5 kHz were 2.1 and 3.53, respectively. © 2020Item Open Access Determination of current transport and trap states density in AlInGaN/GaN heterostructures(Elsevier, 2019) Arslan, Engin; Ural, Sertaç; Altındal, Ş.; Özbay, EkmelThe energy distribution and the relaxation time constant of the trap states with respect to conduction bands in the (Ni/Au) Schottky contact on AlInGaN/GaN heterostructures were investigated using the admittance technique. The potential dependent capacitance/conductance measurements were done in the frequency range of 5 kHz to 5 MHz at a temperature of 300 K. We found strong frequency dispersions at the accumulation regions and at the sharp transition regions (depletion region) in the capacitance curves. High frequency dispersion at the accumulation regions in C-V characteristics indicates that there is a high-density of surface traps between the metal–AlInGaN quaternary layer interfaces. Furthermore, the frequency dispersion at the sharp transition regions behavior can be attributed to the interface traps state between the AlInGaN quaternary layer and GaN layer. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming the models in which traps are located between the metal–AlInGaN interface (surface traps) and between AlInGaN/GaN interfaces (interface traps). The trap states density and time constants of the traps states were calculated as a function of energy separation from the conduction-band edge. The trap states' densities change between 1.3 × 1011 eV−1 cm−2 and 6.2 × 1011 eV−1 cm−2. Also, 4.8 to 5.3 μs time interval calculated for the relaxation times.Item Open Access Determination of scattering mechanisms in AlInGaN/GaN heterostructures grown on sapphire substrate(Elsevier, 2021-01-27) Sonmez, F.; Arslan, Engin; Ardali, S.; Tiras, E.; Özbay, EkmelThe electron mobility limited by different scattering mechanisms in the quaternary AlInGaN alloy grown on a GaN layer is investigated with the classical Hall measurement, which is performed at a temperature range of 12 and 350 K and a magnetic field of B = 0.51 T. The effect of the thickness and alloy composition of the quaternary AlInGaN layer on the mobility is also determined. The experimentally determined temperature-dependent Hall mobility was compared with mobility calculated by using Matthiessen's rule. The main scattering mechanisms, including acoustic phonon scattering (piezoelectric and deformation potential), polar optical phonon scattering, alloy disorder scattering, interface roughness scattering, ionized impurity scattering, dislocation scattering, background impurity scattering, were used in the calculations for all temperatures. The results show that the dominant scattering mechanisms, depending on the investigated sample, are the interface roughness scattering and alloy disorder scattering at almost all temperatures. At a low-temperature, mobility is limited by ionized impurity scattering. High-temperature mobility is limited by polar optical phonon scattering. Furthermore, our results suggest that the thickness and alloy composition of the quaternary AlInGaN layer should be optimized for better transport properties.Item Open Access Effects of the AlN nucleation layer thickness on the crystal structures of an AlN epilayer grown on the 6H-SiC substrate(Taylor & Francis, 2019-04-08) Arslan, Engin; Öztürk, M. K.; Özçelik, S.; Özbay, EkmelThe influence of the LT-AlN(NL) growth times on the mosaic structure parameters of the AlN layer grown on the LT-AlN(NL)/6H-SiC structures as well as the dislocation densities and the strain behaviours in the AlN epilayers has been investigated using XRD measurements. The growth times of the LT-AlN(NL) were changed to 0, 60, 120, 180, and 240 s. We observed that the mosaic structure parameters of the AlN epilayers were slightly affected by the LT-AlN(NL) growth times. However, the dislocation densities in the AlN layer are affected by the growth times of the LT-AlN(NL) layer. The highest edge dislocation density (5.48 × 1010 ± 2.3 × 109 cm−2) was measured for the sample in which 120 s grown LT-AlN(NL) was used. On the other hand, highest screw type dislocation density (1.21 × 1010 ± 1.7 × 109 cm−2) measured in the sample E that contains 240 s growth LT-AlN(NL). The strain calculation results show that the samples without LT-AlN(NL) suffered maximum compressive in-plane strain (−10.9 × 10−3 ± 1.8 × 10−4), which can be suppressed by increasing the LT-AlN(NL) growth times. The out-of-plane strain also has a compressive character and its values increase with LT-AlN(NL) growth times between 60 and 180 s. Same out-of-plane strain values were measured for the LT-AlN(NL) growth times of 180 and 240 s. Furthermore, the form of the biaxial stress in the AlN epilayer changed from compressive to tensile when the LT-AlN(NL) growth times were greater than 120 s.Item Open Access Intersection behavior of the current–voltage (I–V) characteristics of the (Au/Ni)/HfAlO3/n-Si (MIS) structure depends on the lighting intensity(Springer, 2020) Arslan, Engin; Badali, Y.; Altındal, Ş.; Özbay, EkmelThe current–voltage (I–V) and capacitance–voltage (C–V) behaviors of the (Au/Ni)/HfAlO3/n-Si (MIS) junctions at room temperature under white light with various intensities were investigated. The ln(I)–V curves show two linear behavior regions at about 1 V before and after the point of intersection that can be defined as two separate current-conduction (CMs) Mechanisms. The values of the ideality factor (n) and the zero-bias barrier height (ΦB0) were extracted using the slope and intercept of the ln(I)–V curve before and after the intersection point based on lighting power. Although the ΦB0 values decrease with increasing light power, n increases for two regions, and there is a strong linear relationship between them. The values of photo-current (Iph) increase with the increasing lighting power due to the formation of electron–hole pairs. The slope of the double-logarithmic Iph–P was changed from 0.422 to 0.852, respectively, at − 2 V and − 9 V, which indicates the ongoing distribution of Nss. In addition, the profile of surface states (Nss) ionized by light was obtained from the capacitance measured in dark and under lighting at 1 MHz. The Nss–V curve has two characteristic peaks that correspond to the region of depletion and accumulation due to a special distribution of Nss and their restructuring and reordering under the effects of lighting and an electric field.Item Open Access Investigation of trap states in AlInN/AlN/GaN heterostructures by frequency-dependent admittance analysis(Springer US, 2010-09-17) Arslan, Engin; Bütün, Serkan; Şafak, Yasemin; Özbay, EkmelWe present a systematic study on the admittance characterization of surface trap states in unpassivated and SiN x -passivated Al 0.83In 0.17N/AlN/GaN heterostructures. C-V and G/ω-V measurements were carried out in the frequency range of 1 kHz to 1 MHz, and an equivalent circuit model was used to analyze the experimental data. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming models in which traps are located at the metal-AlInN surface. The density (D t) and time constant (τ t) of the surface trap states have been determined as a function of energy separation from the conduction-band edge (E c - E t). The D st and τ st values of the surface trap states for the unpassivated samples were found to be D st≅ (4 - 13)× 10 12 eV - 1 cm - 2 and τ st ≈ 3 μs to 7 μs, respectively. For the passivated sample, D st decreased to 1.5× 10 12eV - 1cm - 2 and τ st to 1.8 μs to 2 μs. The density of surface trap states in Al 0.83In 0.17N/AlN/GaN heterostructures decreased by approximately one order of magnitude with SiN x passivation, indicating that the SiN x insulator layer between the metal contact and the surface of the Al 0.83In 0.17N layer can passivate surface states.Item Open Access A novel hot carrier-induced blue light-emitting device(Elsevier, 2021-05-24) Mutlu, S.; Erol, A.; Arslan, Engin; Özbay, Ekmel; Lisesivdin, S. B.; Tiras, E.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.Item Embargo Plasma-enhanced atomic layer deposition of amorphous Ga2O3 gate dielectrics(Elsevier Ltd, 2022-08-30) Badali, Y.; Arslan, Engin; Ulusoy Ghobadi, Turkan Gamze; Ozbay, Ekmel; Ozcelik, S.Amorphous gallium oxide (Ga2O3) thin films were investigated as gate dielectrics for electronic device applications using plasma-enhanced atomic layer deposition. The structural and morphological properties as well as the electrical and dielectric behaviors of Ga2O3 thin films were explored. The surface morphology of the amorphous Ga2O3 thin film was highly smooth with root mean square of 0.55 nm and low defect density, which were visible to atomic force microscopy. The grazing incidence X-ray diffraction pattern showed no discernible peak, indicating that the film was amorphous. The X-ray photoelectron spectroscopy depth-profiling analysis showed that the Ga/O ratio was 0.76, slightly more than the optimum 2/3 ratio (0.67). The temperature-dependent current–voltage characteristics of the Au/Ni/Ga2O3/p-Si structure revealed that ideality factor and barrier height values decreased and increased with increasing temperature, respectively, demonstrating their high temperature dependency. Regardless of the applied frequency, Ga2O3 thin films exhibited a good dielectric constant of about ∼9 at zero bias voltage. The comprehensive capacitance–voltage analysis showed low trap densities of about 1012 eV−1 cm−2 at the Ga2O3–p-Si interface.Item Open Access Scattering analysis of ultrathin barrier (<7 nm) GaN‑based heterostructures(Springer, 2019) Narin, P.; Arslan, Engin; Öztürk, M.; Öztürk, Mustafa; Lisesivdin, S. B.; Özbay, EkmelIn this study, two-dimensional electron gas (2DEG) mobility analysis of AlN/GaN and InAlN/GaN structures with ultrathin barrier layers by metal organic chemical vapor deposition (MOCVD) has been performed with Hall efect measurements which is carried out under temperature from 15 to 350 K and a single magnetic feld of 0.5 T. As a result of the scattering analysis made with Matthiessen’s rule, it is shown that while the interface roughness scattering mechanism is dominated on the 2DEG mobility at low temperatures, the 2DEG mobility has been dominated by the polar optical phonon-scattering mechanism at high temperatures. Also, the acoustic phonon-scattering mechanism is efective on the 2DEG mobility at middle temperature. Furthermore, the interface and the quantum well parameters such as deformation potential, quantum well width, and correlation length of the interface are determined for each. As well as experimental measurements, the conduction band energy diagrams of the studied samples have been calculated using one-dimensional (1D) self-consistent Schrödinger–Poisson equations. A 2D quasitriangular quantum well formation has been shown for each studied samples. 2DEG probability density of samples has been investigated.Item Open Access Thermal annealing effects on the electrical and structural properties of Ni/Pt Schottky contacts on the quaternary AlInGaN epilayer(Springer US, 2019) Arslan, Engin; Altındal, Ş.; Ural, Sertaç; Kayal, Ömer A.; Öztürk, Mustafa; Özbay, EkmelPt/Au, Ni/Au, Ni/Pt/Au Schottky contacts were placed on a quaternary Al0.84In0.13Ga0.03N epilayer. The electrical and structural properties of the as-deposited Pt/Au, Ni/Au, Ni/Pt/Au and annealed Ni/Pt/Au Schottky contacts were investigated as a function of annealing temperature using current–voltage (I–V), capacitance–voltage (C–V), and high resolution x-ray diffraction measurements (HR-XRD). According to the I–V, Norde, and C–V methods, the highest Schottky barrier height (SBH) was obtained for the Pt/Au (0.82 eV (I–V), 0.83 eV (Norde), and 1.09 eV (C–V)) contacts when they were compared with the other as-deposited Schottky contacts. The estimated SBH of the annealed Ni/Pt/Au Schottky contacts, calculated from the I–V results, were 0.80 eV, 0.79 eV, and 0.78 eV at 300°C, 400°C, and 500°C, respectively. The SBH decreases with an increase in the annealing temperature up to 500°C compared with that of the as-deposited Ni/Pt/Au Schottky contact. The observed extra peaks in the annealed samples confirm the formation of a new interfacial phase at the interface. However, the diffraction patterns of the annealed Schottky contacts did not change as a function of the annealing temperature. The higher ideality factors values were obtained for as-deposited Pt/Au (5.69), Ni/Au (6.09), and Ni/Pt/Au (6.42) Schottky contacts and annealed Ni/Pt/Au (6.42) Schottky contacts at 300°C (6.89), 400°C (7.43), and 500°C (8.04). The higher n results can be attributed to current-transport mechanisms other than thermionic emission, such as dislocation related tunneling.