Browsing by Subject "Gallium arsenide semiconductors."

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Open Access
Design of GaN-based coplanar multi-octave band medium power power MMIC amplifiers
(2013) Eren, Gülesin
Wideband amplifiers are employed in many applications such as military radar, electronic warfare and electronic instrumentations and systems, etc. This thesis project aims to build a wideband medium power monolithic microwave integrated circuits (MMIC) amplifier which operates between 6 and 18 GHz by using 0.25 µm Gallium Nitride (GaN) based high electron mobility transistor (HEMT) technology. Fully monolithic microwave integrated circuits realized with gallium nitride (GaN) high electron mobility transistors are preferred for designing and implementing microwave and millimeter wave power amplifiers due to its superior properties like high breakdown voltage, high current density, high thermal conductivity and high saturation current. Large band gap energy and high saturation velocity of AlGaN/GaN high electron mobility transistors (HEMTs) are more attractive features for high power applications in comparison to the conventional material used in industry for power applications- gallium arsenide (GaAs). Besides the high power capability of GaN enables us to make devices with relatively smaller sizes than of GaAs based devices for the same output power. Device impedances in GaN technology are higher than the GaAs technology which makes broadband matching easier. Firstly, GaN material properties are overviewed by mentioning the design and characterization process of the AlGaN/GaN epitaxial layers grown by Bilkent NANOTAM. After the microfabrication process carried out by Bilkent NANOTAM is explained step by step. It is followed by characterization of the fabricated HEMTs. As a final step before going through the design phase, the small signal and large signal modeling considerations for GaN based HEMTs are presented. In the last part, designs of three different multi-octave MMIC amplifier realized with coplanar waveguide (CPW) elements are discussed. In order to extend the bandwidth and to obtain a flat gain response, two different design approaches are followed, the first one is realized with Chebyshev impedance matching technique without feedback circuit (CMwoFB) and the other one is utilized by Chebyshev Impedance matching technique with negative shunt feedback (CMwFB), respectively. To maximize the output power, two transistors in parallel (PT) are used by introducing Chebyshev matching circuit and negative feedback circuit. The design topology which consists of two parallel transistors (PT) is modified to fulfill all the design requirements and it is implemented by taking process variations and the previously obtained measurement results into account. The measurement and the simulation results match each other very well, the small signal gain is 7.9 ± 0.9 dB and the saturation output power in the bandwidth is higher than 27 dBm in this second iteration.
Open Access
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.
Open Access
Fabrication, modeling and characterization of GaN HEMTs, and design of high power MMIC amplifiers
(2009) Acar, Muhammed A.
Open Access
Low temperature grown GaAs based resonant cavity enhanced photodiodes
(2004) Bütün, Bayram
High performance photodetectors operating in the 1.3 - 1.6 µm wavelength range are vital components for long-haul optical fiber communication systems. GaAs with its mature fabrication methods is one of the most used semiconductors in photodetector technology, but with a low cut-off wavelength around 870 nm. To use GaAs at longer wavelengths, a new growth technique has been developed, in which GaAs was grown at low temperatures (LT-GaAs), so that it absorbs photons with wavelengths up to 1.7 µm. In this work, we report the design, growth, fabrication, and characterization of GaAs-based high-speed p-i-n photodiodes operating at 1.55 µm. A LT-GaAs layer was used as the absorption layer and the photoresponse was selectively enhanced at 1.55 µm using a resonant cavity detector structure. The bottom mirror of the resonant cavity was formed by a highly reflective 15-pair GaAs/AlAs Bragg mirror. Molecular beam epitaxy was used for wafer growth, where the active LT-GaAs layer was grown at a substrate temperature of 200 °C. The fabricated devices exhibited resonance around 1548 nm. When compared to the efficiency of a conventional single-pass detector, an enhancement factor of 7.5 was achieved. Temporal pulse-response measurements were carried out at 1.55 µm. Fast pulse responses with 30 ps pulse-width and a corresponding 3-dB bandwidth of 11.2 GHz was measured.