Browsing by Subject "Electron traps"
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Item Open Access A comprehensive analysis of GaN HEMTs: electro-mechanical behavior, defect generation, and drain LAG reduction with HfO2 layers(Bilkent University, 2023-07) Güneş, BurakGallium Nitride High Electron Mobility Transistors (GaN HEMTs) have rapidly emerged as a transformative technology, owing to the unique properties of the substrate material. They are poised to become a revolutionary advancement in RF amplifier applications, primarily due to their capability to operate at high frequencies and power levels with superior efficiency compared to conventional devices. Despite the rapid progressions, a noticeable gap persists in the literature regarding the relation-ship between mechanical stresses, defect generation, and their subsequent impact on the electrical characteristics of AlGaN/GaN HEMTs. Moreover, current dispersion effects, which are trapping induced reductions in output power, continues to remain a pressing issue. To address these limitations, this study first adopts a multifaceted approach and integrates mechanical simulations and Raman spectroscopy, in order to resolve fine details of stress distributions that a diffraction-limited Raman probe cannot resolve. This enables an extensive modeling of stresses in a typical HEMT structure and helps elucidate the underlying dynamics of defect generation, with the ultimate goal of informing and guiding the development of advanced fabrication techniques. In a second study, an ultrathin blanket dielectric deposition approach was devised to alleviate surface trapping, and consequently, mitigate current dispersion. The proposed streamlined fabrication process yielded a substantial improvement in device performance without compromising the transistor transfer characteristics.Item Open Access The ground state and vortices in a two-dimensional Bose gas confined in a harmonic trap(Institute of Physics Publishing, 2002) Tanatar, BilalWe study the ground state properties of a two-dimensional Bose gas in an harmonic trap potential using the recently proposed mean-field equation that takes into account the correct dimensionality effect. In contrast to the threedimensional case, the interaction term depends logarithmically on the scattering length and density. We compare our results with other approaches with various forms for the two-dimensional coupling. We also consider the vortex states and study the effects of density-dependent interactions on the formation of vortices.Item Open Access q-Gaussian trial function in high density Bose-Einstein condensates(Elsevier Science B.V., 2003) Erdemir, E.; Tanatar, BilalWe study the ground-state static properties of Bose-Einstein condensates in the high density regime using a trial wave function of the form of a q-Gaussian. The flexibility afforded by a q-Gaussian trial function yields very accurate ground-state energies for large number of particles. The resulting condensate wave function profiles are also in good agreement in the high density regime. Comparing our results with those of numerical calculations we provide information on the possible limitations of the q-Gaussian trial functions.Item Open Access Strongly interacting one-dimensional Bose-Einstein condensates in harmonic traps(American Physical Society, 2000) Tanatar, Bilal; Erkan, K.The properties of strongly interacting one dimensional boson condensates in harmonic trap potentials were studied. An equation describing the condensate wave function in the limit of very strong interactions between the bosons was obtained using a density functional type formalism. It was found that the two component system exhibits coexisting and segregated phases similar to the weakly interacting system.Item Open Access Surface-state emission enhancement in white-luminophor CdS nanocrystals using localized plasmon coupling(IEEE, 2008-11) Özel, Tuncay; Soğancı, İbrahim Murat; Nizamoğlu, Sedat; Huyal, İlkem Özge; Mutlugün, Evren; Sapra, S.; Gaponik, N.; Eychmüller, A.; Demir, Hilmi VolkanTo make surface-state emission stronger than band-edge emission for the first time, we proposed and demonstrated plasmon coupling of the surface-state emission from the traps in these CdS nano-luminophors using localized plasmons.Item Open Access Thermally stimulated current observation of trapping centers in undoped GaSe layered single crystals(Wiley, 2001) Gasanly, N. M.; Aydınlı, A.; Salihoglu, Ö.Undoped p-GaSe layered single crystals were grown using Bridgman technique. Thermally stimulated current measurements in the temperature range of 10-300 K were performed at a heating rate of 0.18 K/s. The analysis of the data revealed three trap levels at 0.02, 0.10 and 0.26 eV. The calculation for these traps yielded 8.8 × 10-27, 1.9 × 10-25, and 3.2 × 10-21 cm2 for capture cross sections and 3.2 × 1014, 1.1 × 1016, and 1.2 × 1016 cm-3 for the concentrations, respectively.Item Open Access Thermally stimulated currents in layered Ga4SeS3 semiconductor(2004) Aytekin, S.; Yuksek, N.S.; Goktepe, M.; Gasanly, N.M.; Aydınlı, AtillaThermally stimulated current (TSC) measurements are carried out on nominally undoped Ga4SeS3 layered semiconductor samples with the current flowing along the c-axis in the temperature range of 10 to 150 K. The results are analyzed according to various methods, such as curve fitting, initial rise and Chcn's methods, which seem to be in good agreement with each other. Experimental evidence is found for the presence of three trapping centers in Ga4SeS3 with activation energies of 70, 210 and 357 meV. The calculation yielded 7.9 × 10-21,7.0 × 10 -19 and 1.5 × 10-13 cm2 for the capture cross section, and 1.6 × 1010, 6.5 × 1010 and 1.2 × 1011 cm-3 for the concentration of the traps studied. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinlteim.Item Open Access Trapping centers in undoped GaS layered single crystals(Springer, 2003) Gasanly, N. M.; Aydınlı, Atilla; Yüksek, N. S.; Salihoglu, Ö.Nominally undoped p-GaS layered single crystals were grown using the Bridgman technique. Thermally stimulated current measurements in the temperature range 10-300 K were performed at a heating rate of 0.10 K/s. The analysis of the data revealed six trap levels at 0.05, 0.06, 0.12, 0.63, 0.71, and 0.75 eV. The calculations for these traps yielded 1.2 × 10-21, 2.9 × 10-23, 2.4 × 10-21, 8.0 × 10-9, 1.9 × 10-9 and 4.3 × 10-10 cm2 for the capture cross sections and 1.6 × 1013, 5.0 × 1012, 7.3 × 1012, 1.2 × 1014, 8.9 × 1013 and 2.6 × 1013 cm-3 for the concentrations, respectively.Item Open Access Two-dimensional boson-fermion mixtures in harmonic traps(Elsevier Science B.V., 2003) Tanatar, Bilal; Erdemir, E.The density profiles of bosonic and fermionic components in a system of trapped two-dimensional (2D) boson-fermion (BF) mixture are studied. We employ the variational approach to minimize the total energy functional of the BF mixture subject to the conservation of particle numbers of the species. We consider repulsive interactions between bosons and investigate the repulsive and attractive interactions between bosons and fermions. Our results are qualitatively similar to those in 3D, despite the fact that the structure of equations in 2D are different.