Browsing by Subject "GaAs"

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    Electrical conduction properties of Si δ-doped GaAs grown by MBE
    (2009) Yildiz, A.; Lisesivdin, S.B.; Altuntas H.; Kasap, M.; Ozcelik, S.
    The temperature dependent Hall effect and resistivity measurements of Si δ-doped GaAs are performed in a temperature range of 25-300 K. The temperature dependence of carrier concentration shows a characteristic minimum at about 200 K, which indicates a transition from the conduction band conduction to the impurity band conduction. The temperature dependence of the conductivity results are in agreement with terms due to conduction band conduction and localized state hopping conduction in the impurity band. It is found that the transport properties of Si δ-doped GaAs are mainly governed by the dislocation scattering mechanism at high temperatures. On the other hand, the conductivity follows the Mott variable range hopping conduction (VRH) at low temperatures in the studied structures. © 2009 Elsevier B.V. All rights reserved.
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    Fabrication, characterization, and extraction of GaAs mesfets
    (1994) Ata, Erhan Polatkan
    Metal Semiconductor Field Effect Transistor (MESFET) is the most widely used active element of today’s microwave industry. After development of the MESFET technology, the microwave industry gained a high acceleration, especially in the telecommunication field. In this study, GaAs MESFETs with various dimesions and geometries were fabricated. Characterization and parameter extraction of these devices were performed, by means of low and high frequency measurements. The low cutoff frequency of the MESFETs produced were attributed to the non-optimized gate recess etch.
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    Linear electro-optic coefficient in multilayer self-organized InAs quantum dot structures
    (IEEE, 2007) Akca, B. Imran; Dana, Aykutlu; Aydınlı, Atilla; Rossetti, M.; Li L.; Dagli, N.; Fiore, A.
    The electro-optic coefficients of self-organized InAs quantum dot layers in molecular beam epitaxy grown laser structures in reverse bias have been investigated. Enhanced electrooptic coefficients compared to bulk GaAs were observed. © 2003 Optical Society of America.
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    Modulation in InAs quantum dot waveguides
    (Optical Society of America, 2007) Akca, B. Imran; Dana, Aykutlu; Aydınlı, Atilla; Rossetti, M.; Li L.; Fiore, A.; Dagli, N.
    Modulation in molecular beam epitaxy grown self-assembled InAs quantum dot waveguides have been studied at 1500 nm as a function of wavelength and voltage. Enhanced electro-optic coefficients compared to bulk GaAs were observed. © 2007 Optical Society of America.
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    Room temperature scanning Hall probe microscopy using GaAs/AlGaAs and Bi micro-hall probes
    (Elsevier Science B.V., 2002) Sandhu, A.; Masuda, H.; Oral, A.; Yamada, A.; Konagai, M.
    A room temperature scanning Hall probe microscope system utilizing GaAs/AlGaAs and bismuth micro-Hall probes was used for magnetic imaging of ferromagnetic domain structures on the surfaces of crystalline thin film garnets and permanent magnets. The Bi micro-Hall probes had dimensions ranging between 0.25 and 2.8μm2 and were fabricated using a combination of optical lithography and focused ion beam milling. The use of bismuth was found to overcome surface depletion effects associated with semiconducting micro-Hall probes. Our experiments demonstrated that Bi is a practical choice of material for fabricating sub-micron sized Hall sensors.
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    Stability of two dimensional (2D) structures based on GaAs
    (2015-08) Erol, Mustafa
    Graphene is a two dimensional material isolated for the first time in 2004. After this, two dimensional materials has become an appealing research area for the scientists because of their exotic properties. In search for two dimensional materials, both experimental and theoretical investigations have been carried out. First-principles approaches have been used to predict silicene and germane theoretically. A technologically important semiconductor material is GaAs, however there is no report of two dimensional materials which is based on GaAs. We attempted to find a new stable 2D structure which is formed from either Ga and As atoms based on GaAs or its functionalized form with O atoms. In search for such a system, we performed density functional theory based calculations by using a plane-wave pseudopotential method. We used local density approximation for the exchange correlation potential. First, we performed geometrical optimization calculation in order to identify possible stable structures. We obtained electron band diagrams and phonon dispersion relations to check electronic properties and stability of these materials. We found three structures which are based on GaAs (100), (110) and (110) surfaces. We found that these two dimensional materials are geometrically stable but after performing phonon calculations we observe that there are some negative energy modes. In addition we identified one system which is based on Ga, As, and O atoms. Even though this structure is stable after geometry optimization, it has negative phonon modes in its phonon band diagrams.
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    X-band low phase noise mmic vco & high power mmic spdt design
    (2014) Osmanoğlu, Sinan
    Generally the tuning bandwidth (BW) of a VCO is smaller than the tuning BW of the resonant circuit itself. Using proper components with right topology can handle this problem. In order to overcome this problem and improve the tuning BW of the VCO, common-base inductive feedback topology with Gallium Arsenide (GaAs) Heterojunction Bipolar Transistor (HBT) is used and an optimized topology for tank circuit is selected to minimize the effect of bandwidth limiting components. Designed VCO with this topology achived -117 dBc/Hz at 1 MHz offset phase noise with 9-13 dBm output power between 8.8-11.4 GHz band. Second part of the thesis composed of Single Pole Double Throw (SPDT) RF Switch design. From mesa resistors to SPDT fabrication, everything is fabricated using Bilkent University NANOTAM Gallium Nitride (GaN) on Silicon Carbide (SiC) process. Switching HEMTs are fabricated to generate a model to design SPDTs and the final design works between DC-12 GHz with less than 1.4 dB insertion loss (IL), -20 dB isolation and 14.5 dB return loss (RL) at worst case. The power handling of the switches are better than 40 dBm at output with 0.2 dB compression, which is measured with continuous wave (CW) signal at 10 GHz.