Browsing by Subject "Semiconducting gallium arsenide"

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Open Access
1.3 μm GaAs based resonant cavity enhanced Schottky barrier internal photoemission photodetector
(IEEE, Piscataway, NJ, United States, 2000) Necmi, B.; Kimukin, I.; Özbay, Ekmel; Tuttle, G.
GaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism were fabricated. Quantum efficiency (QE) was increased using resonant cavity enhancement (RCE) effect.
Open Access
100-GHz resonant cavity enhanced Schottky photodiodes
(Institute of Electrical and Electronics Engineers, 1998) Onat, B. M.; Gökkavas, M.; Özbay, Ekmel; Ata, E. P.; Towe, E.; Ünlü, M. S.
Resonant cavity enhanced (RCE) photodiodes are promising candidates for applications in optical communications and interconnects where ultrafast high-efficiency detection is desirable. We have designed and fabricated RCE Schottky photodiodes in the (Al, In) GaAs material system for 900-nm wavelength. The observed temporal response with 10-ps pulsewidth was limited by the measurement setup and a conservative estimation of the bandwidth corresponds to more than 100 GHz. A direct comparison of RCE versus conventional detector performance was performed by high speed measurements under optical excitation at resonant wavelength (895 nm) and at 840 nm where the device functions as a single-pass conventional photodiode. A more than two-fold bandwidth enhancement with the RCE detection scheme was demonstrated.
Open Access
45-GHz bandwidth-efficiency resonant-cavity-enhanced ITO-Schottky photodiodes
(IEEE, 2001) Bıyıklı, Necmi; Kimukin, I.; Aytür, O.; Gökkavas, M.; Ünlü, M. S.; Özbay, Ekmel
High-speed Schottky photodiodes suffer from low efficiency mainly due to the thin absorption layers and the semitransparent Schottky-contact metals. We have designed, fabricated and characterized high-speed and high-efficiency AlGaAs-GaAs-based Schottky photodiodes using transparent indium-tin-oxide Schottky contact material and resonant cavity enhanced detector structure. The measured devices displayed resonance peaks around 820 nm with 75% maximum peak efficiency and an experimental setup limited temporal response of 11 ps pulsewidth. The resulting 45-GHz bandwidth-efficiency product obtained from these devices corresponds to the best performance reported to date for vertically illuminated Schottky photodiodes.
Open Access
Anisotropy sensitivity of an acoustic lens with slit aperture
(IEEE, 1993) Atalar, Abdullah; Ishikawa, I.; Ogura, Y.; Tomita, K.
A conventional spherical acoustic lens is modified by restricting its aperture in the form of a slit to provide directional sensitivity. The spacing between the two parallel absorbing sheets forming the slit is adjustable to obtain varying slit widths. The resulting lens can be used in conjunction with V(Z) method to obtain leaky wave velocities of the sample under investigation as a function of direction. The theoretical V(Z) analysis of the lens involves a two-dimensional integral rather than one-dimensional integral of the conventional lens. Single crystal anisotropic materials are chosen as test samples. Reflection coefficients for anisotropic single crystals of given surface cut and orientation are calculated. Numerically evaluated V(Z) curves are used to deduce the surface wave velocity of the object for the given orientation. This is compared with the surface wave velocity directly calculated from the elastic parameters of the object. Results show the compromise between signal-to-noise ratio and angular resolution as the slit width is varied. V(Z) measurement results of a slitted lens are presented to be compared with calculated curves. The new lens is used to measure the acoustic velocity on the (001) surface of GaAs along varying directions with differing slit widths.
Open Access
Design considerations for MMIC distributed amplifiers
(IEEE, 1994) Ergun, Şanlı; Atalar, Abdullah
The bandwidth of the input artificial line in a distributed amplifier is the main band limiting factor. By choosing this impedance properly the bandwidth of a distributed amplifier can be maximized. A four section GaAs MESFET distributed amplifier is designed using this strategy. The fabricated MMIC amplifier gives satisfactory performance. By adding proper length of series transmission lines in the drain side, the gain and the gain flatness of the amplifier can be further improved. This fact is presented via simulation results. The superior gain potential of cascode connected FETs is also demonstrated.
Open Access
Direct magnetic imaging of ferromagnetic domain structures by room temperature scanning hall probe microscopy using a bismuth micro-Hall probe
(Japan Society of Applied Physics, 2001) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
A bismuth micro-Hall probe sensor with an integrated scanning tunnelling microscope tip was incorporated into a room temperature scanning Hall probe microscope system and successfully used for the direct magnetic imaging of microscopic domains of low coercivity perpendicular garnet thin films and demagnetized strontium ferrite permanent magnets. At a driving current of 800 μA, the Hall coefficient, magnetic field sensitivity and spatial resolution of the Bi probe were 3.3 × 10-4 Ω/G, 0.38 G/√Hz and ∼ 2.8 μm, respectively. The room temperature magnetic field sensitivity of the Bi probe was comparable to that of a semiconducting 1.2μm GaAs/AlGaAs heterostructure micro-Hall probe, which exhibited a value of 0.41 G/√Hz at a maximum driving current of 2μA.
Open Access
Exchange-correlation effects in the impurity-limited mobility of GaAs quantum wires
(Sci Tech Res Counc Turkey, Ankara, Turkey, 1999) Tanatar, Bilal
We study the many-body effects described by the local-field corrections on the mobility of quasi-one dimensional electron systems. The low temperature mobility due to remote-impurity doping and interface-roughness scattering is calculated within the relaxation time approximation. We find that correlation effects significantly reduce the mobility at low density.
Open Access
Fabrication of high-speed resonant cavity enhanced schottky photodiodes
(Institute of Electrical and Electronics Engineers, 1997-05) Özbay, Ekmel; Islam, M. S.; Onat, B.; Gökkavas, M.; Aytür, O.; Tuttle, G.; Towe, E.; Henderson, R. H.; Ünlü, M. S.
We report the fabrication and testing of a GaAs-based high-speed resonant cavity enhanced (RCE) Schottky photodiode. The top-illuminated RCE detector is constructed by integrating a Schottky contact, a thin absorption region (In0.8Ga0.92As) and a distributed AlAs-GaAs Bragg mirror. The Schottky contact metal serves as a high-reflectivity top mirror in the RCE detector structure. The devices were fabricated by using a microwave-compatible fabrication process. The resulting spectral photo response had a resonance around 895 nm, in good agreement with our simulations. The full-width-at-half-maximum (FWHM) was 15 nm, and the enhancement factor was in excess of 6. The photodiode had an experimental setup limited temporal response of 18 ps FWHM, corresponding to a 3-dB bandwidth of 20 GHz.
Open Access
Filtering characteristics of hybrid integrated polymer and compound semiconductor waveguides
(IEEE, 2002) Ozturk, C.; Huntington, A.; Aydınlı, Atilla; Byun, Y.T.; Dagli, N.
This paper reports a study on a compact filter fabricated using hybrid integration of compound semiconductors and polymers. A GaAs epilayer is glued onto a polymer channel waveguide forming a highly asymmetrical directional coupler. This approach results in a narrow band filter due to very different dispersion characteristics of the compound semiconductor and the polymer materials. Furthermore, fiber coupling loss has been significantly reduced, since the input and output coupling is done through the polymer waveguide. Filtering characteristics can be engineered by changing the thickness and the length of the semiconductor epilayer. This can be done precisely using etch stop layers and noncritical lithography. The spectral response of such a filter can also be tuned electronically either using the electro-optic properties of the compound semiconductor or the thermo-optic properties of the polymer.
Open Access
High-speed 1.3 μm GaAs internal photoemission resonant cavity enhanced photodetector
(IEEE, 2000) Kimukin, İbrahim; Özbay, Ekmel; Bıyıklı, Necmi; Kartaloğlu, Tolga; Aytür, Orhan; Tuttle, G.
Resonant cavity enhanced (RCE) photodetectors offer the possibility of overcoming the low quantum efficiency limitation of conventional photodetectors. The RCE detectors are based on the enhancement of the optical field within a Fabry-Perot resonator. The increased field allows the use of a thin absorbing layer, which minimizes the transit time of the photogenerated carriers without hampering the quantum efficiency. Recently, we fabricated high-speed RCE p-i-n and Schottky photodetectors, where a 90% quantum efficiency along with a 3-dB bandwidth of 50 GHz has been reported. We used the transfer matrix method to design the epilayer structure and to simulate the optical properties of the photodiode. The samples were fabricated by a microwave-compatible process and high-speed measurements were made with an optical parametric oscillator.
Open Access
High-speed 1.55 μm operation of low-temperature-grown GaAs-based resonant-cavity-enhanced p-i-n photodiodes
(American Institute of Physics, 2004) Butun, B.; Bıyıklı, Necmi; Kimukin, I.; Aytur, O.; Özbay, Ekmel; Postigo, P. A.; Silveira, J. P.; Alija, A. R.
The 1.55 μm high-speed operation of GaAs-based p-i-n photodiodes was demonstrated and their design, growth and fabrication were discussed. A resonant-cavity-detector structure was used to selectively enhance the photoresponse at 1.55 μm. The bottom mirror of the resonant cavity was formed by a highly reflecting 15-pair GaAs/AlAs Bragg mirror and molecular-beam epitaxy was used for wafer growth. It was found that the fabricated devices exhibited a resonance of around 1548 nm and an enhancement factor of 7.5 was achieved when compared to the efficiency of a single-pass detector.
Open Access
High-speed GaAs-based resonant-cavity-enhanced 1.3-μm photodetector
(SPIE, 2000) Özbay, Ekmel; Kimukin, İbrahim; Bıyıklı, Necmi; Gary, T.
High-speed photodetectors operating at 1.3 and 1.55 μm are important for long distance fiber optic based telecommunication applications. We fabricated GaAs based photodetectors operating at 1.3 μm that depend on internal photoemission as the absorption mechanism. Detectors using internal photoemission have usually very low quantum efficiency. We increased the quantum efficiency using resonant cavity enhancement effect. Resonant cavity enhancement effect also introduced wavelength selectivity which is very important for wavelength division multiplexing based communication systems. The top-illuminated Schottky photodiodes were fabricated by a microwave-compatible monolithic microfabrication process. The top metal layer serves as the top mirror of the Fabry-Perot cavity. Bottom mirror is composed of 15 pair AlAs/GaAs distributed Bragg reflector. We have used transfer matrix method to simulate the optical properties of the photodiodes. Our room temperature quantum efficiency measurement and simulation of our photodiodes at zero bias show that, we have achieved 9 fold enhancement in the quantum efficiency, with respect to a similar photodetector without a cavity. We also investigated the effect of reverse bias on quantum efficiency. Our devices are RC time constant limited with a predicted 3-dB bandwidth of 70 GHz.
Open Access
High-Speed InSb photodetectors on GaAs for mid-IR applications
(IEEE, 2004) Kimukin, I.; Bıyıklı, Necmi; Kartaloǧlu, T.; Aytür, O.; Özbay, Ekmel
We report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06 × 10 -6 cm 2 to 2.25 × 10 -4 cm 2 measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 Ω cm 2. At 77 K, spectral measurements yielded high responsivity between 3 and 5 μm with the cutoff wavelength of 5.33 μm. The maximum responsivity tor 80-μm diameter detectors was 1.00 × 10 5 V/W at 435 μm while the detectivity was 3.41×10 9 cm Hz 1/2/W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 μm with the pump at 780 mm. 30-μm diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.
Open Access
High-speed widely-tunable >90% quantum-efficiency resonant cavity enhanced p-i-n photodiodes
(IEEE, 1998) Bıyıklı, Necmi; Kimukin, İbrahim; Aytür, Orhan; Gökkavas, M.; Ulu, G.; Mirin, R.; Christensen, D. H.; Ünlü, M. S.; Özbay, Ekmel
Widely-tunable high-speed resonant cavity enhanced p-i-n photodiodes were designed, fabricated and tested for operation around 820 nm. The structure was grown by solid-source MBE on GaAs substrates and features high-reflectivity Bragg mirrors made of quarter-wave Al0.20Ga0.80As/AlAs stacks. Photoresponse and photospectral measurements were carried out. The tuning of the resonance wavelength within the Bragg mirror's upper and lower edges was observed. Quantum efficiency greater than 90% was demonstrated.
Open Access
Hydrodynamic approach for modelling transport in quantum well device structures
(Institute of Physics Publishing Ltd., 1998) Besikci, C.; Tanatar, Bilal; Sen, O.
A semiclassical approach for modelling electron transport in quantum well structures is presented. The model is based on the balance equations governing the conservation of particle density, momentum and energy with Monte Carlo (MC) generated transport parameters. Three valleys of the conduction band, size quantization in the Γ valley, and the lowest two subbands in the quantum well are considered by taking the detailed intersubband dynamics into account. The transport parameters of the model are extracted from steady-state MC simulations based on an improved formulation of two-dimensional polar optical phonon scattering including screening effects. The predictions of the proposed model have been found to be in excellent agreement with those of the ensemble MC simulations under both time varying and spatially nonuniform fields. The calculated transport parameters which are of interest for device modelling are presented as a function of the electron energy for the AIGaAs/GaAs quantum well. The model serves as an accurate semiclassical alternative to costly ensemble MC simulations for studying the transport in quantum well structures and for the modelling and optimization of submicron devices based on these structures, such as modulation doped field-effect transistors (MODFETs).
Open Access
In-situ focused ion beam implantation for the fabrication of a hot electron transistor oscillator structure
(1996) Kaya I.I.; Dellow, M.W.; Bending, S.J.; Linfield, E.H.; Rose P.D.; Ritchie, D.A.; Jones G.A.C.
Recent advances using in situ focused ion beam implantation during an MBE growth interruption have been exploited to fabricate planar GaAs hot electron structures without the need for shallow ohmic contacts. This novel fabrication route shows a very high yield and has been used to demonstrate a prototype high-frequency oscillator structure based on electron multiplication in the base layer. Existing devices show transfer factors in excess of unity as well as reversal of the base current at high injection levels, which are the prerequisites for oscillator action. Future improvements in device design are discussed.
Open Access
Magnetic-field dependence of low-temperature mobility in quasi-one-dimensional electron systems
(Institute of Physics Publishing Ltd., 1994) Tanatar, Bilal; Constantinou, N. C.
We study the mobility of a quasi-one-dimensional (Q1D) electron system in the presence of an axial magnetic field at low temperatures. We consider the mobility limits for remote-impurity scattering, homogeneous-background scattering, interface-roughness scattering, and alloy-disorder scattering mechanisms. For a system in which all carriers are in the lowest subband, the electron-impurity interaction is modelled for the above cases, and analytic expressions are derived. Calculations appropriate for a GaAs Q1D structure are presented for typical wire radius R, electron density N, impurity density Ni, and applied magnetic field B.
Open Access
Model study of a surfactant on the GaAs(100) surface
(Elsevier, 2002-11-01) Consorte, C. D.; Fong, C. Y.; Watson, M. D.; Yang, L. H.; Çıracı, Salim
Based on the facts that: (a) the transverse acoustic vibrational branch frequency is softened at the Brillouin zone boundaries of crystalline GaAs; (b) at the surface, the Ga-As bond is stronger than Ga-Te bond; and (c) the requirement that the final bond orientation of the Te surfactant should be rotated by 90degrees with respect to its initial orientation, we carried out a model study of an exchange process in epitaxial growth of GaAs (100). Even with very restrictive conditions imposed on the atomic movements, this study explains why Te is an effective surfactant for this type of growth. (C) 2002 Elsevier Science B.V. All rights reserved.
Open Access
Quantum mechanical simulation of charge transport in very small semiconductor structures
(IEEE, 1989) Yalabik, M. C.; Diff, K.
A quantum mechanical simulation method of charge transport in very small semiconductor devices, based on the numerical solution of the time-dependent Schrödinger equation (coupled self-consistently to the Poisson equation to determine the electrostatic potential in the device), is presented. Carrier transport is considered within the effective mass approximation, while the effects of the electron-phonon interaction are included in an approximation that is consistent with the results of the perturbation theory and gives the correct two-point time correlation function. Numerical results for the transient behavior of a planar ultrasubmicrometer three-dimensional GaAs MESFET (gate length of 26 nm) are also presented. They indicate that extremely fast gate-step response times (switching times) characterize such short-channel GaAs devices. © 1989 IEEE
Open Access
Quantum size effect on the phonon-induced Zeeman splitting in a GaAs quantum dot with Gaussian and parabolic confining potentials
(Elsevier B.V., 2008) Mukhopadhyaya, S.; Boyacioglu, B.; Saglam, M.; Chatterjee, A.
The Zeeman splitting of the ground and the first excited level of a Gaussian GaAs quantum dot is studied in the presence of electron-longitudinal-optical (LO)-phonon interaction incorporating the spin of the electron and is compared with the case of a parabolic dot. It is shown that the Zeeman splitting is suppressed because of the polaronic interaction and becomes strongly size dependent, but the parabolic confinement overestimates this Zeeman suppression. It is also shown that although the energy levels are split because of the spin-field interaction, the cyclotron frequencies and the Zeeman lines are independent of the electron spin in the dipole transition. © 2008 Elsevier B.V. All rights reserved.