Browsing by Subject "AlGaN/GaN"
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Item Open Access Analysis of defect related optical transitions in biased AlGaN/GaN heterostructures(2010) Bengi, A.; Lisesivdin, S.B.; Kasap, M.; Mammadov, T.; Ozcelik, S.; Özbay, EkmelThe optical transitions in AlGaN/GaN heterostructures that are grown by metalorganic chemical vapor deposition (MOCVD) have been investigated in detail by using Hall and room temperature (RT) photoluminescence (PL) measurements. The Hall measurements show that there is two-dimensional electron gas (2DEG) conduction at the AlGaN/GaN heterointerface. PL measurements show that in addition to the characteristic near-band edge (BE) transition, there are blue (BL) and yellow luminescence (YL) bands, free-exciton transition (FE), and a neighboring emission band (NEB). To analyze these transitions in detail, the PL measurements were taken under bias where the applied electric field changed from 0 to 50 V/cm. Due to the applied electric field, band bending occurs and NEB separates into two different peaks as an ultraviolet luminescence (UVL) and Y4 band. Among these bands, only the yellow band is unaffected with the applied electric field. The luminescence intensity change of these bands with an electric field is investigated in detail. As a result, the most probable candidate of the intensity decrease with an increasing electric field is the reduction in the radiative lifetime. © 2010 Elsevier Ltd. All rights reserved.Item Open Access The effect of strain relaxation on electron transport in undoped Al0.25Ga0.75N/GaN heterostructures(Elsevier BV * North-Holland, 2007-11-01) Lişesivdin, S. B.; Yıldız, A.; Acar, S.; Kasap, M.; Özçelik, S.; Özbay, EkmelThe two-dimensional electron gas (2DEG) transport properties of two-step growth undoped Al0.25Ga0.75N/GaN heterostructures with semi-insulating buffer, grown by MOCVD, were investigated in a temperature range of 20–350 K. Using the quantitative mobility spectrum analysis (QMSA) method, it was shown that significant parallel conduction does not occur in worked structures. In-plain growth axis strains are calculated using the total polarization-induced charge density taken as the sheet carrier density measured from the Hall effect. It was found that the calculated strain values are in good agreement with those reported. Influences of the two-step growth parameters such as growth ramp time, the annealing temperature of the GaN nucleation layer on the mobility, and density of the 2DEG are also discussed.Item Open Access High power K-band GaN on SiC CPW monolithic power amplifier(IEEE, 2014-10) Cengiz, Ömer; Şen, Özlem; Özbay, EkmelThis paper presents a high power amplifier at K-band (20.2-21.2 GHz). The AlGaN/GaN CPW MMIC amplifier is realized with 0.25 μm HEMT process on 2-inch semi-insulating SiC substrate. The amplifier has a small signal gain over 20 dB for Vds=15V and measured output power of over 31 dBm at 20.2 Ghz. PAE of the amplifier is around 22% for desired frequency band. Initial radiation hardness tests indicate a suitable stability of the technology in space. © 2014 European Microwave Association.Item Open Access Realistic channel temperature simulation of AlGaN/GaN high electron mobility transistors(IEEE, 2019) Odabaşı, Oğuz; Bütün, Bayram; Özbay, EkmelIn this work, the realistic channel temperature of AlGaN/GaN High Electron Mobility Transistors (HEMTs) is investigated by using 2D electrothermal and Finite Element Method (FEM) thermal simulations. By using a special method to map the position dependent heating in a device, more accurate results in channel temperature are achieved compared to the conventional FEM methods. With this method, larger device areas can be simulated more accurately with less complexity.Item Open Access Scattering analysis of two-dimensional electrons in AlGaN/GaN with bulk related parameters extracted by simple parallel conduction extraction method(American Institute of Physics, 2010-07-15) Lisesivdin, S. B.; Yildiz, A.; Balkan, N.; Kasap, M.; Ozcelik, S.; Özbay, EkmelWe carried out the temperature (22-350 K) and magnetic field (0.05 and 1.4 T) dependent Hall mobility and carrier density measurements on Al 0.22Ga0.78N/GaN heterostructures with AlN interlayer grown by metal-organic chemical-vapor deposition. Hall data is analyzed with a simple parallel conduction extraction method and temperature dependent mobility and carrier densities of the bulk and two-dimensional (2D) electrons are extracted successfully. The results for the bulk carriers are discussed using a theoretical model that includes the most important scattering mechanisms that contribute to the mobility. In order to investigate the mobility of two-dimensional electron gas, we used a theoretical model that takes into account the polar optical phonon scattering, acoustic phonon scattering, background impurity scattering, and interface roughness scattering in 2D. In these calculations, the values are used for the deformation potential and ionized impurity density values were obtained from the bulk scattering analysis. Therefore, the number of fitting parameters was reduced from four to two. © 2010 American Institute of Physics.Item Open Access Strain calculations from hall measurements in undoped Al 0.25Ga0.75N/GaN HEMT structures(American Institute of Physics, 2007) Lişesivdin, S. B.; Yıldız, A.; Kasap, M.; Özbay, EkmelThe transport properties of undoped Al0.25Ga0.75N/GaN HEMT structures grown by MOCVD were investigated in a temperature range of 20 K-350 K. With Quantitative Mobility Spectrum Analysis (QMSA) method; it was found that, all conduction in undoped Al0.25Ga0.75N/GaN HEMT structures belong to the two dimensional electron gas (2DEG). With the acception of Hall sheet carrier density is the total polarization induced charge density, strains of 2DEG interfaces were calculated. Calculated strain values are in good agreement with the literature. Effects of the growth parameters of the nucleation layers of samples on the mobility and density of the 2DEG are listed.Item Open Access Temperature dependent negative capacitance behavior in (Ni/Au)/AlGaN/AIN/GaN heterostructures(Elsevier, 2010-02-10) Arslan, E.; Safak, Y.; Altindal, S.; Kelekci, O.; Özbay, EkmelThe temperature dependent capacitance voltage (C-V) and conductance voltage (G/omega-V) characteristics of (Ni/Au)/Al(0.22)Ga(0.78)N/AlN/GaN heterostructures were investigated by considering the series resistance (R(s)) effect in the temperature range of 80-390 K. The experimental results show that the values of C and G/omega are strongly functioning of temperature and bias voltage. The values of C cross at a certain forward bias voltage point (similar to 2.8 V) and then change to negative values for each temperature, which is known as negative capacitance (NC) behavior. In order to explain the NC behavior, we drawn the C vs I and G/omega vs I plots for various temperatures at the same bias voltage. The negativity of the C decreases with increasing temperature at the forward bias voltage, and this decrement in the NC corresponds to the increment of the conductance. When the temperature was increased, the value of C decreased and the intersection point shifted towards the zero bias direction. This behavior of the C and G/omega values can be attributed to an increase in the polarization and the introduction of more carriers in the structure. R(s) values increase with increasing temperature. Such temperature dependence is in obvious disagreement with the negative temperature coefficient of R or G reported in the literature. The intersection behavior of C-V curves and the increase in R(s) with temperature can be explained by the lack of free charge carriers, especially at low temperatures.Item Open Access X band GaN based MMIC power amplifier with 36.5dBm P1-dB for space applications(IEEE, 2018) Gürdal, Armağan; Yılmaz, Burak Alptuğ; Cengiz, Ömer; Sen, Özlem; Özbay, EkmelAn X-Band Monolithic Microwave Integrated Circuit (MMIC) High Power Amplifier (HPA) with coplanar waveguide (CPW) based on AlGaN/GaN on SiC technology is presented in this paper. Coplanar waveguide technology (CPW) is chosen for the simplicity and reduced cost of fabrication since CPW process has no via. High Electron Mobility Transistors (HEMTs) are matched for the 8 GHz-8.4GHz frequency band for maximum output power. The Amplifier has a small signal gain over 10 dB, output power of 36.5dBm at 1 dB gain compression point (P1dB) and 40% power added efficiency (PAE) at (PldB) in the desired frequency band (8 GHz-8.4 GHz) with Vds = 30V.