Yazar "Topaloglu, S." seçeneğine göre listele

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    ICP-RIE etching of self-aligned InP based HBTs with Cl-2/N-2 chemistry
    (ELSEVIER SCIENCE BV, 2011) Topaloglu, S.; Prost, W.; Tegude, F. -J.
    We report on a simple Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE) process with Cl-2/N-2 chemistry to process InP based, self-aligned HBTs with sub-micron emitters. Since the layer to be etched is in the range of 150 nm (the thickness of emitter cap and emitter layers), a low etch rate is beneficial. On the other hand, it is also necessary to use chemistries without hydrogen to prevent any possible hydrogen passivation. Therefore, in this work, Cl-2/N-2 chemistry is selected and a plasma process providing an etch rate of 120 nm/min is optimized. Not only the etch rate but also the electrical and the surface quality of the wafers are examined. It has been illustrated that the etch rate of the optimized process is uniform over the wafer and it is reproducible. In addition to that, it has been shown with electrical measurements that there is no degradation in the material quality. To test the optimized process. sub-micron HBTs are fabricated and the RF measurements have shown an f(max) of 340 GHz which make them to be used in high speed communication systems. In addition to that, lower and controlled under etch gives better current gain distribution over the wafer leading better device models and resulting in better yield in MMICs. (C) 2011 Elsevier B.V. All rights reserved.
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    Optical properties of heavily doped GaAs nanowires and electroluminescent nanowire structures
    (IOP PUBLISHING LTD, 2011) Lysov, A.; Offer, M.; Gutsche, C.; Regolin, I.; Topaloglu, S.; Geller, M.; Prost, W.; Tegude, F-J
    We present GaAs electroluminescent nanowire structures fabricated by metal organic vapor phase epitaxy. Electroluminescent structures were realized in both axial pn-junctions in single GaAs nanowires and free-standing nanowire arrays with a pn-junction formed between nanowires and substrate, respectively. The electroluminescence emission peak from single nanowire pn-junctions at 10 K was registered at an energy of around 1.32 eV and shifted to 1.4 eV with an increasing current. The line is attributed to the recombination in the compensated region present in the nanowire due to the memory effect of the vapor-liquid-solid growth mechanism. Arrayed nanowire electroluminescent structures with a pn-junction formed between nanowires and substrate demonstrated at 5 K a strong electroluminescence peak at 1.488 eV and two shoulder peaks at 1.455 and 1.519 eV. The main emission line was attributed to the recombination in the p-doped GaAs. The other two lines correspond to the tunneling-assisted photon emission and band-edge recombination in the abrupt junction, respectively. Electroluminescence spectra are compared with the micro-photoluminescence spectra taken along the single p-, n- and single nanowire pn-junctions to find the origin of the electroluminescence peaks, the distribution of doping species and the sharpness of the junctions.
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    Three-input single-output second-order filters using current-feedback amplifiers
    (ELSEVIER GMBH, URBAN & FISCHER VERLAG, 2012) Topaloglu, S.; Sagbas, M.; Anday, F.
    In this study, a novel second order universal filter using current-feedback amplifier, commercially available active component, is presented. The signal-flow graph method is used to synthesize the filter. The proposed filter has three high impedance input and one output, (multiple input single output (MISO) configuration). It can generate all biquadratic filtering functions namely: low-pass (LP), band-pass (BP), high-pass (HP), band-reject (BR) and all-pass (AP) at the output terminal by selecting different input signal combinations. The validity of the proposed circuits is demonstrated by simulations. (C) 2011 Elsevier GmbH. All rights reserved.