Browsing by Subject "2DEG"

Filter results by typing the first few letters
Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen 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, Ekmel
    The 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.
  • Thumbnail Image
    ItemOpen Access
    Effect of various pseudomorphic AIN layer insertions on the electron densities of two-dimensional electron gas in lattice-matched In0.18AI0.82N/GaN based heterostructures
    (Institutul National de Cercetare-Dezvoltare pentru Optoelectronica, 2009) Lisesivdin, S. B.; Özbay, Ekmel
    We explored the effects of various pseudomorphic AlN layer insertions in lattice-matched In0.18Al0.82N/GaN based heterostructures on band structures and carrier densities with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. According to the calculations, important increase in carrier density is expected with an increasing number of AlN insertions in In0.18Al0.82N barrier. The effect of the position of an AlN layer in In0.18Al0.82N barrier is also investigated. An additional AlN layer insertion in the GaN layer is calculated in detail with the help of an experimental point of view, in which the possible effects on both carrier density and mobility are discussed.
  • Thumbnail Image
    ItemOpen Access
    Numerical optimization of Al-mole fractions and layer thicknesses in normally-on AlGaN-GaN double-channel high electron mobility transistors (DCHEMTs)
    (Institutul National de Cercetare-Dezvoltare pentru Optoelectronica, 2009-05) Atmaca, G.; Elibol, K.; Lisesivdin, S. B.; Kasap, M.; Özbay, Ekmel
    We explored the effects of the Al-mole fraction (x) of AlxGa1-xN barrier layers and the thickness of some layers on carrier densities and electron probability densities in normally-on AlGaN-GaN double-channel high electron mobility transistors. Investigations were carried out by solving nonlinear Schrodinger-Poisson equations, self-consistently including polarization induced carriers that are important for GaN-based heterostructures and twodimensional electron gas (2DEG) formation. Strain relaxation limits were also calculated, in which optimized cases were found for the investigated Al-mole fraction and thickness values under pseudomorphic limits. The effect of the investigated thickness changes on electron probability densities show no important change in the overall simulations. In addition to a carrier increase in the selected optimum cases, reasonable mobility behavior is also expected.
  • Thumbnail Image
    ItemOpen Access
    Numerical optimization of In-mole fractions and layer thicknesses in AlxGa1-xN/AlN/GaN high electron mobility transistors with InGaN back barriers
    (ELSEVIER, 2011-02-01) Kelekci, O.; Lisesivdin, S. B.; Ozcelik, S.; Özbay, Ekmel
    The effects of the In-mole fraction (x) of an InxGa 1-xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1-yN/AlN/GaN/InxGa 1-xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear SchrdingerPoisson equations. Strain relaxation limits were also calculated for the investigated AlyGa1-yN barrier layer and InxGa1-xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed.
  • Thumbnail Image
    ItemOpen 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, Ekmel
    The 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.
  • Thumbnail Image
    ItemOpen Access
    Well parameters of two-dimensional electron gas in Al0.88In 0.12N/AlN/GaN/AlN heterostructures grown by MOCVD
    (Wiley, 2009-12-01) Tasli, P.; Lisesivdin, S. B.; Yildiz, A.; Kasap, M.; Arslan, E.; Özcelik, S.; Özbay, Ekmel
    Resistivity and Hall effect measurements were carried out as a function of magnetic field (0-1.5 T) and temperature (30-300 K) for Al0.88In 0.12N/AlN/GaN/AlN heterostructures grown by Metal Organic Chemical Vapor Deposition (MOCVD). Magnetic field dependent Hall data were analyzed by using the quantitative mobility spectrum analysis (QMSA). A two-dimensional electron gas (2DEG) channel located at the Al0.88In 0.12N/GaN interface with an AlN interlayer and a two-dimensional hole gas (2DHG) channel located at the GaN/AlN interface were determined for Al 0.88In0.12N/AlN/GaN/AlN heterostructures. The interface parameters, such as quantum well width, the deformation potential constant and correlation length as well as the dominant scattering mechanisms for the Al 0.88In0.12N/GaN interface with an AlN interlayer were determined from scattering analyses based on the exact 2DEG carrier density and mobility obtained with QMSA