Feedback-enhanced sensitivity in optomechanics

DEFF Research Database (Denmark)

Harris, Glen I.; Andersen, Ulrik L.; Knittel, Joachim

2012-01-01

The intracavity power, and hence sensitivity, of optomechanical sensors is commonly limited by parametric instability. Here we characterize the degradation of sensitivity induced by parametric instability in a micron-scale cavity optomechanical system. Feedback via optomechanical transduction...... and electrical gradient force actuation is applied to suppress the parametric instability. As a result a 5.4-fold increase in mechanical motion transduction sensitivity is achieved to a final value of 1.9×10-18 mHz-1/2....

Optomechanical transistor with mechanical gain

Science.gov (United States)

Zhang, X. Z.; Tian, Lin; Li, Yong

2018-04-01

We study an optomechanical transistor, where an input field can be transferred and amplified unidirectionally in a cyclic three-mode optomechanical system. In this system, the mechanical resonator is coupled simultaneously to two cavity modes. We show that it only requires a finite mechanical gain to achieve the nonreciprocal amplification. Here the nonreciprocity is caused by the phase difference between the linearized optomechanical couplings that breaks the time-reversal symmetry of this system. The amplification arises from the mechanical gain, which provides an effective phonon bath that pumps the mechanical mode coherently. This effect is analogous to the stimulated emission of atoms, where the probe field can be amplified when its frequency is in resonance with that of the anti-Stokes transition. We show that by choosing optimal parameters, this optomechanical transistor can reach perfect unidirectionality accompanied with strong amplification. In addition, the presence of the mechanical gain can result in ultralong delay in the phase of the probe field, which provides an alternative to controlling light transport in optomechanical systems.

Proposal for an optomechanical traveling wave phonon-photon translator

Energy Technology Data Exchange (ETDEWEB)

Safavi-Naeini, Amir H; Painter, Oskar, E-mail: safavi@caltech.edu, E-mail: opainter@caltech.edu [Thomas J Watson, Sr., Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125 (United States)

2011-01-15

In this paper, we describe a general optomechanical system for converting photons to phonons in an efficient and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator (PPT) formed from coupled photonic and phononic crystal planar circuits. The application of the PPT to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits, is considered.

Strain engineering of quantum dots for long wavelength emission: Photoluminescence from self-assembled InAs quantum dots grown on GaAs(001) at wavelengths over 1.55 μm

International Nuclear Information System (INIS)

Shimomura, K.; Kamiya, I.

2015-01-01

Photoluminescence (PL) at wavelengths over 1.55 μm from self-assembled InAs quantum dots (QDs) grown on GaAs(001) is observed at room temperature (RT) and 4 K using a bilayer structure with thin cap. The PL peak has been known to redshift with decreasing cap layer thickness, although accompanying intensity decrease and peak broadening. With our strain-controlled bilayer structure, the PL intensity can be comparable to the ordinary QDs while realizing peak emission wavelength of 1.61 μm at 4 K and 1.73 μm at RT. The key issue lies in the control of strain not only in the QDs but also in the cap layer. By combining with underlying seed QD layer, we realize strain-driven bandgap engineering through control of strain in the QD and cap layers

Strain engineering of quantum dots for long wavelength emission: Photoluminescence from self-assembled InAs quantum dots grown on GaAs(001) at wavelengths over 1.55 μm

Energy Technology Data Exchange (ETDEWEB)

Shimomura, K., E-mail: sd12502@toyota-ti.ac.jp; Kamiya, I., E-mail: kamiya@toyota-ti.ac.jp [Toyota Technological Institute 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)

2015-02-23

Photoluminescence (PL) at wavelengths over 1.55 μm from self-assembled InAs quantum dots (QDs) grown on GaAs(001) is observed at room temperature (RT) and 4 K using a bilayer structure with thin cap. The PL peak has been known to redshift with decreasing cap layer thickness, although accompanying intensity decrease and peak broadening. With our strain-controlled bilayer structure, the PL intensity can be comparable to the ordinary QDs while realizing peak emission wavelength of 1.61 μm at 4 K and 1.73 μm at RT. The key issue lies in the control of strain not only in the QDs but also in the cap layer. By combining with underlying seed QD layer, we realize strain-driven bandgap engineering through control of strain in the QD and cap layers.

Quantum control of optomechanical systems

International Nuclear Information System (INIS)

Hofer, S.

2015-01-01

This thesis explores the prospects of entanglement-enhanced quantum control of optomechanical systems. We first discuss several pulsed schemes in which the radiation-pressure interaction is used to generate EPR entanglement between the mechanical mode of a cavity-optomechanical system and a travelling-wave light pulse. The entanglement created in this way can be used as a resource for mechanical state preparation. On the basis of this protocol, we introduce an optomechanical teleportation scheme to transfer an arbitrary light state onto the mechanical system. Furthermore, we describe how one can create a mechanical non-classical state (i.e., a state with a negative Wigner function) by single-photon detection, and, in a similar protocol, how optomechanical systems can be used to demonstrate the violation of a Bell inequality. The second part of the thesis is dedicated to time-continuous quantum control protocols. Making use of optimal-control techniques, we analyse measurement-based feedback cooling of a mechanical oscillator and demonstrate that ground-state cooling is achievable in the sideband-resolved, blue-detuned regime. We then extend this homodyne-detection based setup and introduce the notion of a time-continuous Bell measurement---a generalisation of the standard continuous variable Bell measurement to a continuous measurement setting. Combining this concept with continuous feedback we analyse the generation of a squeezed mechanical steady state via time-continuous teleportation, and the creation of bipartite mechanical entanglement by entanglement swapping. Finally we discuss an experiment demonstrating the evaluation of the conditional optomechanical quantum state by Kalman filtering, constituting a important step towards time-continuous quantum control of optomechanical systems and the possible realisation of the protocols presented in this thesis. (author) [de

Pump-probe studies of travelling coherent longitudinal acoustic phonon oscillations in GaAs

Energy Technology Data Exchange (ETDEWEB)

Xu, Y.; Qi, J.; Tolk, Norman [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235 (United States); Miller, J. [Naval air Warfare Center Weapons Division, China Lake, CA 93555 (United States); Cho, Y.J.; Liu, X.; Furdyna, J.K. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Shahbazyan, T.V. [Department of Physics, Jackson State University, MS 39217 (United States)

2008-07-01

We report comprehensive studies of long-lived oscillations in femtosecond optical pump-probe measurements on GaAs based systems. The oscillations arise from a photo-generated coherent longitudinal acoustic phonon wave at the sample surface, which subsequently travels from the surface into the GaAs substrate, thus providing information on the optical properties of the material as a function of time/depth. Wavelength-dependent studies of the oscillations near the bandgap of GaAs indicate strong correlations to the optical properties of GaAs. We also use the coherent longitudinal acoustic phonon waves to probe a thin buried Ga{sub 0.1}In{sub 0.9}As layers non-invasively. The observed phonon oscillations experience a reduction in amplitude and a phase change at wavelengths near the bandgap of the GaAs, when it passes through the thin Ga{sub x}In{sub 1-x}As layer. The layer depth and thicknesses can be extracted from the oscillation responses. A model has been developed that satisfactorily characterizes the experimental results. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

The GAAS metagenomic tool and its estimations of viral and microbial average genome size in four major biomes.

Science.gov (United States)

Angly, Florent E; Willner, Dana; Prieto-Davó, Alejandra; Edwards, Robert A; Schmieder, Robert; Vega-Thurber, Rebecca; Antonopoulos, Dionysios A; Barott, Katie; Cottrell, Matthew T; Desnues, Christelle; Dinsdale, Elizabeth A; Furlan, Mike; Haynes, Matthew; Henn, Matthew R; Hu, Yongfei; Kirchman, David L; McDole, Tracey; McPherson, John D; Meyer, Folker; Miller, R Michael; Mundt, Egbert; Naviaux, Robert K; Rodriguez-Mueller, Beltran; Stevens, Rick; Wegley, Linda; Zhang, Lixin; Zhu, Baoli; Rohwer, Forest

2009-12-01

Metagenomic studies characterize both the composition and diversity of uncultured viral and microbial communities. BLAST-based comparisons have typically been used for such analyses; however, sampling biases, high percentages of unknown sequences, and the use of arbitrary thresholds to find significant similarities can decrease the accuracy and validity of estimates. Here, we present Genome relative Abundance and Average Size (GAAS), a complete software package that provides improved estimates of community composition and average genome length for metagenomes in both textual and graphical formats. GAAS implements a novel methodology to control for sampling bias via length normalization, to adjust for multiple BLAST similarities by similarity weighting, and to select significant similarities using relative alignment lengths. In benchmark tests, the GAAS method was robust to both high percentages of unknown sequences and to variations in metagenomic sequence read lengths. Re-analysis of the Sargasso Sea virome using GAAS indicated that standard methodologies for metagenomic analysis may dramatically underestimate the abundance and importance of organisms with small genomes in environmental systems. Using GAAS, we conducted a meta-analysis of microbial and viral average genome lengths in over 150 metagenomes from four biomes to determine whether genome lengths vary consistently between and within biomes, and between microbial and viral communities from the same environment. Significant differences between biomes and within aquatic sub-biomes (oceans, hypersaline systems, freshwater, and microbialites) suggested that average genome length is a fundamental property of environments driven by factors at the sub-biome level. The behavior of paired viral and microbial metagenomes from the same environment indicated that microbial and viral average genome sizes are independent of each other, but indicative of community responses to stressors and environmental conditions.

The dependence of the wavelength on MBE growth parameters of GaAs quantum dot in AlGaAs NWs on Si (111) substrate

Science.gov (United States)

Reznik, R. R.; Shtrom, I. V.; Samsonenko, Yu B.; Khrebtov, A. I.; Soshnikov, I. P.; Cirlin, G. E.

2017-11-01

The data on the growth peculiarities and physical properties of GaAs insertions embedded in AlGaAs nanowires grown on Si (111) substrates by Au-assisted molecular beam epitaxy are presented. It is shown that by varying of the growth parameters it is possible to form structures like quantum dots emitting in a wide wavelengths range for both active and barrier parts. The technology proposed opens new possibilities for the integration of direct-band AIIIBV materials on silicon platform.

The GAAS metagenomic tool and its estimations of viral and microbial average genome size in four major biomes.

Directory of Open Access Journals (Sweden)

Florent E Angly

2009-12-01

Full Text Available Metagenomic studies characterize both the composition and diversity of uncultured viral and microbial communities. BLAST-based comparisons have typically been used for such analyses; however, sampling biases, high percentages of unknown sequences, and the use of arbitrary thresholds to find significant similarities can decrease the accuracy and validity of estimates. Here, we present Genome relative Abundance and Average Size (GAAS, a complete software package that provides improved estimates of community composition and average genome length for metagenomes in both textual and graphical formats. GAAS implements a novel methodology to control for sampling bias via length normalization, to adjust for multiple BLAST similarities by similarity weighting, and to select significant similarities using relative alignment lengths. In benchmark tests, the GAAS method was robust to both high percentages of unknown sequences and to variations in metagenomic sequence read lengths. Re-analysis of the Sargasso Sea virome using GAAS indicated that standard methodologies for metagenomic analysis may dramatically underestimate the abundance and importance of organisms with small genomes in environmental systems. Using GAAS, we conducted a meta-analysis of microbial and viral average genome lengths in over 150 metagenomes from four biomes to determine whether genome lengths vary consistently between and within biomes, and between microbial and viral communities from the same environment. Significant differences between biomes and within aquatic sub-biomes (oceans, hypersaline systems, freshwater, and microbialites suggested that average genome length is a fundamental property of environments driven by factors at the sub-biome level. The behavior of paired viral and microbial metagenomes from the same environment indicated that microbial and viral average genome sizes are independent of each other, but indicative of community responses to stressors and

Cavity Optomechanics at Millikelvin Temperatures

Science.gov (United States)

Meenehan, Sean Michael

The field of cavity optomechanics, which concerns the coupling of a mechanical object's motion to the electromagnetic field of a high finesse cavity, allows for exquisitely sensitive measurements of mechanical motion, from large-scale gravitational wave detection to microscale accelerometers. Moreover, it provides a potential means to control and engineer the state of a macroscopic mechanical object at the quantum level, provided one can realize sufficiently strong interaction strengths relative to the ambient thermal noise. Recent experiments utilizing the optomechanical interaction to cool mechanical resonators to their motional quantum ground state allow for a variety of quantum engineering applications, including preparation of non-classical mechanical states and coherent optical to microwave conversion. Optomechanical crystals (OMCs), in which bandgaps for both optical and mechanical waves can be introduced through patterning of a material, provide one particularly attractive means for realizing strong interactions between high-frequency mechanical resonators and near-infrared light. Beyond the usual paradigm of cavity optomechanics involving isolated single mechanical elements, OMCs can also be fashioned into planar circuits for photons and phonons, and arrays of optomechanical elements can be interconnected via optical and acoustic waveguides. Such coupled OMC arrays have been proposed as a way to realize quantum optomechanical memories, nanomechanical circuits for continuous variable quantum information processing and phononic quantum networks, and as a platform for engineering and studying quantum many-body physics of optomechanical meta-materials. However, while ground state occupancies (that is, average phonon occupancies less than one) have been achieved in OMC cavities utilizing laser cooling techniques, parasitic absorption and the concomitant degradation of the mechanical quality factor fundamentally limit this approach. On the other hand, the high

Colloquium: cavity optomechanics

CERN Multimedia

2011-01-01

Monday 14 November 2011, 17:00 Ecole de Physique, Auditoire Stueckelberg Université de Genève Cavity optomechanics: controlling micro mechanical oscillators with laser light Prof. Tobias Kippenberg EPFL, Lausanne Laser light can be used to cool and to control trapped ions, atoms and molecules at the quantum level. This has lead to spectacular advances such as the most precise atomic clocks. An outstanding frontier is the control with lasers of nano- and micro-mechancial systems. Recent advances in cavity optomechanics have allowed such elementary control for the first time, enabling mechanical systems to be ground state cooled leading to readout with quantum limited sensitivity and permitting to explore new device concepts resulting from radiation pressure.  

Single-photon blockade in a hybrid cavity-optomechanical system via third-order nonlinearity

Science.gov (United States)

Sarma, Bijita; Sarma, Amarendra K.

2018-04-01

Photon statistics in a weakly driven optomechanical cavity, with Kerr-type nonlinearity, are analyzed both analytically and numerically. The single-photon blockade effect is demonstrated via calculations of the zero-time-delay second-order correlation function g (2)(0). The analytical results obtained by solving the Schrödinger equation are in complete conformity with the results obtained through numerical solution of the quantum master equation. A systematic study on the parameter regime for observing photon blockade in the weak coupling regime is reported. The parameter regime where the photon blockade is not realizable due to the combined effect of nonlinearities owing to the optomechanical coupling and the Kerr-effect is demonstrated. The experimental feasibility with state-of-the-art device parameters is discussed and it is observed that photon blockade could be generated at the telecommunication wavelength. An elaborate analysis of the thermal effects on photon antibunching is presented. The system is found to be robust against pure dephasing-induced decoherences and thermal phonon number fluctuations.

Nonlinear effects in modulated quantum optomechanics

Science.gov (United States)

Yin, Tai-Shuang; Lü, Xin-You; Zheng, Li-Li; Wang, Mei; Li, Sha; Wu, Ying

2017-05-01

The nonlinear quantum regime is crucial for implementing interesting quantum effects, which have wide applications in modern quantum science. Here we propose an effective method to reach the nonlinear quantum regime in a modulated optomechanical system (OMS), which is originally in the weak-coupling regime. The mechanical spring constant and optomechanical interaction are modulated periodically. This leads to the result that the resonant optomechanical interaction can be effectively enhanced into the single-photon strong-coupling regime by the modulation-induced mechanical parametric amplification. Moreover, the amplified phonon noise can be suppressed completely by introducing a squeezed vacuum reservoir, which ultimately leads to the realization of photon blockade in a weakly coupled OMS. The reached nonlinear quantum regime also allows us to engineer the nonclassical states (e.g., Schrödinger cat states) of the cavity field, which are robust against the phonon noise. This work offers an alternative approach to enhance the quantum nonlinearity of an OMS, which should expand the applications of cavity optomechanics in the quantum realm.

Wigner Function Reconstruction in Levitated Optomechanics

Science.gov (United States)

Rashid, Muddassar; Toroš, Marko; Ulbricht, Hendrik

2017-10-01

We demonstrate the reconstruction of theWigner function from marginal distributions of the motion of a single trapped particle using homodyne detection. We show that it is possible to generate quantum states of levitated optomechanical systems even under the efect of continuous measurement by the trapping laser light. We describe the opto-mechanical coupling for the case of the particle trapped by a free-space focused laser beam, explicitly for the case without an optical cavity. We use the scheme to reconstruct the Wigner function of experimental data in perfect agreement with the expected Gaussian distribution of a thermal state of motion. This opens a route for quantum state preparation in levitated optomechanics.

Nano-optomechanics with optically levitated nanoparticles

Science.gov (United States)

Neukirch, Levi P.; Vamivakas, A. Nick

2015-01-01

Nano-optomechanics is a vibrant area of research that continues to push the boundary of quantum science and measurement technology. Recently, it has been realised that the optical forces experienced by polarisable nanoparticles can provide a novel platform for nano-optomechanics with untethered mechanical oscillators. Remarkably, these oscillators are expected to exhibit quality factors approaching ?. The pronounced quality factors are a direct result of the mechanical oscillator being freed from a supporting substrate. This review provides an overview of the basic optical physics underpinning optical trapping and optical levitation experiments, it discusses a number of experimental approaches to optical trapping and finally outlines possible applications of this nano-optomechanics modality in hybrid quantum systems and nanoscale optical metrology.

Microwave GaAs Integrated Circuits On Quartz Substrates

Science.gov (United States)

Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

1994-01-01

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

A picogram- and nanometre-scale photonic-crystal optomechanical cavity.

Science.gov (United States)

Eichenfield, Matt; Camacho, Ryan; Chan, Jasper; Vahala, Kerry J; Painter, Oskar

2009-05-28

The dynamic back-action caused by electromagnetic forces (radiation pressure) in optical and microwave cavities is of growing interest. Back-action cooling, for example, is being pursued as a means of achieving the quantum ground state of macroscopic mechanical oscillators. Work in the optical domain has revolved around millimetre- or micrometre-scale structures using the radiation pressure force. By comparison, in microwave devices, low-loss superconducting structures have been used for gradient-force-mediated coupling to a nanomechanical oscillator of picogram mass. Here we describe measurements of an optical system consisting of a pair of specially patterned nanoscale beams in which optical and mechanical energies are simultaneously localized to a cubic-micron-scale volume, and for which large per-photon optical gradient forces are realized. The resulting scale of the per-photon force and the mass of the structure enable the exploration of cavity optomechanical regimes in which, for example, the mechanical rigidity of the structure is dominantly provided by the internal light field itself. In addition to precision measurement and sensitive force detection, nano-optomechanics may find application in reconfigurable and tunable photonic systems, light-based radio-frequency communication and the generation of giant optical nonlinearities for wavelength conversion and optical buffering.

Multi-shell spherical GaAs /AlxGa1-x As quantum dot shells-size distribution as a mechanism to generate intermediate band energy levels

Science.gov (United States)

Rodríguez-Magdaleno, K. A.; Pérez-Álvarez, R.; Martínez-Orozco, J. C.; Pernas-Salomón, R.

2017-04-01

In this work the generation of an intermediate band of energy levels from multi-shell spherical GaAs /AlxGa1-x As quantum dot shells-size distribution is reported. Within the effective mass approximation the electronic structure of a GaAs spherical quantum-dot surrounded by one, two and three shells is studied in detail using a numerically stable transfer matrix method. We found that a shells-size distribution characterized by continuously wider GaAs domains is a suitable mechanism to generate the intermediate band whose width is also dependent on the Aluminium concentration x. Our results suggest that this effective mechanism can be used for the design of wider intermediate band than reported in other quantum systems with possible solar cells enhanced performance.

Squeezed light in optomechanical systems

DEFF Research Database (Denmark)

Harris, G. I.; Taylor, M. A.; Hoff, Ulrich Busk

2012-01-01

Squeezed light enhanced optomechanical measurements are demonstrated in both intra-cavity and biological contexts, with respective enhancements of 1.0 and 2.7 dB. Quantum enhanced microrheology of the cytoplasm of a yeast cell is thereby realized.......Squeezed light enhanced optomechanical measurements are demonstrated in both intra-cavity and biological contexts, with respective enhancements of 1.0 and 2.7 dB. Quantum enhanced microrheology of the cytoplasm of a yeast cell is thereby realized....

Single-Crystal Diamond Nanobeam Waveguide Optomechanics

Science.gov (United States)

Khanaliloo, Behzad; Jayakumar, Harishankar; Hryciw, Aaron C.; Lake, David P.; Kaviani, Hamidreza; Barclay, Paul E.

2015-10-01

Single-crystal diamond optomechanical devices have the potential to enable fundamental studies and technologies coupling mechanical vibrations to both light and electronic quantum systems. Here, we demonstrate a single-crystal diamond optomechanical system and show that it allows excitation of diamond mechanical resonances into self-oscillations with amplitude >200 nm . The resulting internal stress field is predicted to allow driving of electron spin transitions of diamond nitrogen-vacancy centers. The mechanical resonances have a quality factor >7 ×105 and can be tuned via nonlinear frequency renormalization, while the optomechanical interface has a 150 nm bandwidth and 9.5 fm /√{Hz } sensitivity. In combination, these features make this system a promising platform for interfacing light, nanomechanics, and electron spins.

Two-Photon Pumped Synchronously Mode-Locked Bulk GaAs Laser

Science.gov (United States)

Cao, W. L.; Vaucher, A. M.; Ling, J. D.; Lee, C. H.

1982-04-01

Pulses 7 picoseconds or less in duration have been generated from a bulk GaAs crystal by a synchronous mode-locking technique. The GaAs crystal was optically pumped by two-photon absorption of the emission from a mode-locked Nd:glass laser. Two-photon absorption as the means of excitation increases the volume of the gain medium by increasing the pene-tration depth of the pump intensity, enabling generation of intra-cavity pulses with peak power in the megawatt range. Tuning of the wavelength of the GaAs emission is achieved by varying the temperature. A tuning range covering 840 nm to 885 nm has been observed over a temperature range from 97°K to 260°K. The intensity of the GaAs emission has also been observed to decrease as the temperature of the crystal is increased.

Single-Crystal Diamond Nanobeam Waveguide Optomechanics

Directory of Open Access Journals (Sweden)

Behzad Khanaliloo

2015-12-01

Full Text Available Single-crystal diamond optomechanical devices have the potential to enable fundamental studies and technologies coupling mechanical vibrations to both light and electronic quantum systems. Here, we demonstrate a single-crystal diamond optomechanical system and show that it allows excitation of diamond mechanical resonances into self-oscillations with amplitude >200  nm. The resulting internal stress field is predicted to allow driving of electron spin transitions of diamond nitrogen-vacancy centers. The mechanical resonances have a quality factor >7×10^{5} and can be tuned via nonlinear frequency renormalization, while the optomechanical interface has a 150 nm bandwidth and 9.5  fm/sqrt[Hz] sensitivity. In combination, these features make this system a promising platform for interfacing light, nanomechanics, and electron spins.

Cavity optomechanics in gallium phosphide microdisks

International Nuclear Information System (INIS)

Mitchell, Matthew; Barclay, Paul E.; Hryciw, Aaron C.

2014-01-01

We demonstrate gallium phosphide (GaP) microdisk optical cavities with intrinsic quality factors >2.8 × 10 5 and mode volumes 3 , and study their nonlinear and optomechanical properties. For optical intensities up to 8.0 × 10 4 intracavity photons, we observe optical loss in the microcavity to decrease with increasing intensity, indicating that saturable absorption sites are present in the GaP material, and that two-photon absorption is not significant. We observe optomechanical coupling between optical modes of the microdisk around 1.5 μm and several mechanical resonances, and measure an optical spring effect consistent with a theoretically predicted optomechanical coupling rate g 0 /2π∼30 kHz for the fundamental mechanical radial breathing mode at 488 MHz

Measurement-Induced Macroscopic Superposition States in Cavity Optomechanics

DEFF Research Database (Denmark)

Hoff, Ulrich Busk; Kollath-Bönig, Johann; Neergaard-Nielsen, Jonas Schou

2016-01-01

A novel protocol for generating quantum superpositions of macroscopically distinct states of a bulk mechanical oscillator is proposed, compatible with existing optomechanical devices operating in the bad-cavity limit. By combining a pulsed optomechanical quantum nondemolition (QND) interaction...

Cluster dynamics at different cluster size and incident laser wavelengths

International Nuclear Information System (INIS)

Desai, Tara; Bernardinello, Andrea

2002-01-01

X-ray emission spectra from aluminum clusters of diameter -0.4 μm and gold clusters of dia. ∼1.25 μm are experimentally studied by irradiating the cluster foil targets with 1.06 μm laser, 10 ns (FWHM) at an intensity ∼10 12 W/cm 2 . Aluminum clusters show a different spectra compared to bulk material whereas gold cluster evolve towards bulk gold. Experimental data are analyzed on the basis of cluster dimension, laser wavelength and pulse duration. PIC simulations are performed to study the behavior of clusters at higher intensity I≥10 17 W/cm 2 for different size of the clusters irradiated at different laser wavelengths. Results indicate the dependence of cluster dynamics on cluster size and incident laser wavelength

Preferential adsorption of gallium on GaAs(111)B surfaces during the initial growth of Au-assisted GaAs nanowires

International Nuclear Information System (INIS)

Shu Haibo; Chen Xiaoshuang; Ding Zongling; Dong Ruibin; Lu Wei

2010-01-01

The mechanism of the preferential adsorption of Ga on GaAs(111)B surfaces during the initial growth of Au-assisted GaAs nanowires is studied by using first-principles calculations within density functional theory. The calculated results show that Au preadsorption on GaAs(111)B surface significantly enhances the stability of the Ga adatom in comparison with the adsorption of Ga on clean GaAs(111)B surface. The stabilization of the Ga adatom is due to charge transfers from the Ga 4p and 4s states to the Au 6s and As 4p states. The number of Ga adatoms stabilized on GaAs(111)B surfaces depends on the size of surface Au cluster. The reason is that Au acted as an electron acceptor on GaAs(111)B surface assists the charge transfer of Ga adatoms for filling the partial unoccupied bands of GaAs(111)B surface. Our results are helpful to understand the growth of Au-assisted GaAs nanowires.

Optical extinction dependence on wavelength and size distribution of airborne dust

Science.gov (United States)

Pangle, Garrett E.; Hook, D. A.; Long, Brandon J. N.; Philbrick, C. R.; Hallen, Hans D.

2013-05-01

The optical scattering from laser beams propagating through atmospheric aerosols has been shown to be very useful in describing air pollution aerosol properties. This research explores and extends that capability to particulate matter. The optical properties of Arizona Road Dust (ARD) samples are measured in a chamber that simulates the particle dispersal of dust aerosols in the atmospheric environment. Visible, near infrared, and long wave infrared lasers are used. Optical scattering measurements show the expected dependence of laser wavelength and particle size on the extinction of laser beams. The extinction at long wavelengths demonstrates reduced scattering, but chemical absorption of dust species must be considered. The extinction and depolarization of laser wavelengths interacting with several size cuts of ARD are examined. The measurements include studies of different size distributions, and their evolution over time is recorded by an Aerodynamic Particle Sizer. We analyze the size-dependent extinction and depolarization of ARD. We present a method of predicting extinction for an arbitrary ARD size distribution. These studies provide new insights for understanding the optical propagation of laser beams through airborne particulate matter.

Optomechanics: Diamonds take off

Science.gov (United States)

Hammerer, Klemens; Aspelmeyer, Markus

2015-10-01

Nanodiamonds that are levitated by light and are equipped with internal spin provide a new platform for performing quantum and optomechanical experiments with massive, environmentally isolated objects.

Spectral dependence of the refractive index of single-crystalline GaAs for optical applications

International Nuclear Information System (INIS)

Plotnichenko, V G; Nazaryants, V O; Kryukova, E B; Dianov, E M

2010-01-01

The refractive index of crystalline GaAs is measured by the method of interference refractometry in the wavenumber range from 10 500 to 540 cm -1 (or the wavelength range from 0.9 to 18.6 μm) with a resolution of 0.1 cm -1 . The measurement results are approximated by the generalized Cauchy dispersion formula of the 8th power. Spectral wavelength dependences of the first- and second-order derivatives of the refractive index are calculated, and the zero material dispersion wavelength is found to be λ 0 = 6.61 μm. Using three GaAs plates of different thicknesses we managed to raise the refractive index measurement accuracy up to 4 x 10 -4 or 0.02%, being nearly by an order of magnitude better than the data available.

Optomechanics in a Levitated Droplet of Superfluid Helium

Science.gov (United States)

Brown, Charles; Harris, Glen; Harris, Jack

2017-04-01

A critical issue common to all optomechanical systems is dissipative coupling to the environment, which limits the system's quantum coherence. Superfluid helium's extremely low optical and mechanical dissipation, as well as its high thermal conductivity and its ability cool itself via evaporation, makes the mostly uncharted territory of superfluid optomechanics an exciting avenue for exploring quantum effects in macroscopic objects. I will describe ongoing work that aims to exploit the unique properties of superfluid helium by constructing an optomechanical system consisting of a magnetically levitated droplet of superfluid helium., The optical whispering gallery modes (WGMs) of the droplet, as well as the mechanical oscillations of its surface, should offer exceptionally low dissipation, and should couple to each other via the usual optomechanical interactions. I will present recent progress towards this goal, and also discuss the background for this work, which includes prior demonstrations of magnetic levitation of superfluid helium, high finesse WGMs in liquid drops, and the self-cooling of helium drops in vacuum.

Ultrasensitive and broadband magnetometry with cavity optomechanics

DEFF Research Database (Denmark)

Li, Bei-Bei; Bulla, Douglas; Bilek, Jan

2017-01-01

We achieved sensitivity of 30 pT/Hz1/2 and working bandwidth larger than 100 MHz, using cavity optomechanical magnetometry, and also demonstrated quantum light enhanced sensitivity in such a magnetometer.......We achieved sensitivity of 30 pT/Hz1/2 and working bandwidth larger than 100 MHz, using cavity optomechanical magnetometry, and also demonstrated quantum light enhanced sensitivity in such a magnetometer....

Spectral dependence of the refractive index of single-crystalline GaAs for optical applications

Energy Technology Data Exchange (ETDEWEB)

Plotnichenko, V G; Nazaryants, V O; Kryukova, E B; Dianov, E M, E-mail: victor@fo.gpi.ac.r [Fibre Optics Research Center of the Russian Academy of Sciences, 38 Vavilov Street, Moscow 119333 (Russian Federation)

2010-03-17

The refractive index of crystalline GaAs is measured by the method of interference refractometry in the wavenumber range from 10 500 to 540 cm{sup -1} (or the wavelength range from 0.9 to 18.6 {mu}m) with a resolution of 0.1 cm{sup -1}. The measurement results are approximated by the generalized Cauchy dispersion formula of the 8th power. Spectral wavelength dependences of the first- and second-order derivatives of the refractive index are calculated, and the zero material dispersion wavelength is found to be {lambda}{sub 0} = 6.61 {mu}m. Using three GaAs plates of different thicknesses we managed to raise the refractive index measurement accuracy up to 4 x 10{sup -4} or 0.02%, being nearly by an order of magnitude better than the data available.

Dissipative optomechanics in a Michelson-Sagnac interferometer.

Science.gov (United States)

Xuereb, André; Schnabel, Roman; Hammerer, Klemens

2011-11-18

Dissipative optomechanics studies the coupling of the motion of an optical element to the decay rate of a cavity. We propose and theoretically explore a realization of this system in the optical domain, using a combined Michelson-Sagnac interferometer, which enables a strong and tunable dissipative coupling. Quantum interference in such a setup results in the suppression of the lower motional sideband, leading to strongly enhanced cooling in the non-sideband-resolved regime. With state-of-the-art parameters, ground-state cooling and low-power quantum-limited position transduction are both possible. The possibility of a strong, tunable dissipative coupling opens up a new route towards observation of such fundamental optomechanical effects as nonlinear dynamics. Beyond optomechanics, the suggested method can be readily transferred to other setups involving nonlinear media, atomic ensembles, or single atoms.

Quantum optics of optomechanical networks

International Nuclear Information System (INIS)

Stannigel, K.

2012-01-01

This thesis proposes various setups in which micro-mechanical resonators and optomechanical systems can be combined with other quantum systems, such as solid-state qubits or atomic ensembles, in a beneficial way. These hybrid systems open up new ways for quantum control, and several protocols and applications for quantum information processing and, in particular, for quantum networks are presented. Part I describes an optically mediated coupling between the vibrational modes of a semi-transparent dielectric membrane and the center-of-mass motion of an atomic ensemble. Using the sophisticated toolbox available for the control of atomic systems, this setting enables an indirect manipulation of the membrane, including, for example, cooling it to the vibrational ground state. A fully quantum mechanical treatment of this open system is given in terms of the quantum stochastic Schrödinger equation. In Part II we explore the potential of optomechanical systems for quantum information processing applications. First, we introduce the concept of an optomechanical transducer, where a micro-mechanical resonator mediates an interaction between a solid-state based qubit on the one hand, and photons in an optical cavity on the other hand. The resulting qubit-light interface is shown to enable quantum state transfers between two distant solid-state qubits, thereby making them available for quantum networking applications. Second, we study multi-mode optomechanical systems in the single-photon single-phonon strong coupling regime. We predict quantum signatures of this interaction, which could be observed in future experiments, and provide a route towards possible applications of these systems as quantum information processing units. Part III presents a dissipative state preparation scheme for cascaded quantum networks. In such networks excitations can only propagate along a single spatial direction and the optomechanical transducer represents one way of realizing them. We show, in

GaAs nanocrystals: Structure and vibrational properties

International Nuclear Information System (INIS)

Nayak, J.; Sahu, S.N.; Nozaki, S.

2006-01-01

GaAs nanocrystals were grown on indium tin oxide substrate by an electrodeposition technique. Atomic force microscopic measurement indicates an increase in the size of the nanocrystal with decrease in the electrolysis current density accompanied by the change in the shape of the crystallite. Transmission electron microscopic measurements identify the crystallite sizes to be in the range of 10-15 nm and the crystal structure to be orthorhombic. On account of the quantum size effect, the first optical transition was blue shifted with respect to the band gap of the bulk GaAs and the excitonic peak appeared prominent. A localized phonon mode ascribed to certain point defect occurred in the room temperature micro-Raman spectrum

Nonreciprocal frequency conversion in a multimode microwave optomechanical circuit

Science.gov (United States)

Feofanov, A. K.; Bernier, N. R.; Toth, L. D.; Koottandavida, A.; Kippenberg, T. J.

Nonreciprocal devices such as isolators, circulators, and directional amplifiers are pivotal to quantum signal processing with superconducting circuits. In the microwave domain, commercially available nonreciprocal devices are based on ferrite materials. They are barely compatible with superconducting quantum circuits, lossy, and cannot be integrated on chip. Significant potential exists for implementing non-magnetic chip-scale nonreciprocal devices using microwave optomechanical circuits. Here we demonstrate a possibility of nonreciprocal frequency conversion in a multimode microwave optomechanical circuit using solely optomechanical interaction between modes. The conversion scheme and the results reflecting the actual progress on the experimental implementation of the scheme will be presented.

Effect of AlSb quantum dots on efficiency of GaAs solar cell (Conference Presentation)

Science.gov (United States)

Mansoori, Ahmad; Addamane, Sadhvikas J.; Renteria, Emma J.; Shima, Darryl M.; Hains, Christopher P.; Balakrishnan, Ganesh

2016-09-01

Quantum Dots (QDs) have a broad applications in science and specifically in solar cell. Many research groups show that by adding QDs with lower bandgap respect to host material, the overall absorption of sun spectrum coverage will increase. Here, we propose using QDs with higher band gap respect to host material to improve efficiency of solar cell by improving quantum efficiency. GaAs solar cells have the highest efficiency in single junction solar cells. However, the absorption of GaAs is not good enough in wavelength lower than 550nm. AlSb can absorb shorter wavelength with higher absorption coefficient and also recombination rate should be lower because of higher bandgap of AlSb respect to GaAs. We embed AlSb QDs in GaAs solar cells and results show slight improvement in quantum efficiency and also in overall efficiency. Coverage of AlSb QDs has a direct impact on quality of AlSb QDs and efficiency of cell. In the higher coverage, intermixing between GaAs and AlSb causes to shift bandgap to lower value (having AlGaSb QDs instead of pure AlSb QDs). This intermixing decrease the Voc and overall efficiency of cell. In lower coverage, AlSb can survive from intermixing and overall performance of cell improves. Optimizing growth condition of AlSb QDs is a key point for this work. By using AlSb QDs, we can decrease the thickness of active layer of GaAs solar cells and have a thinner solar cell.

Femtosecond pulsed laser ablation of GaAs

International Nuclear Information System (INIS)

Trelenberg, T.W.; Dinh, L.N.; Saw, C.K.; Stuart, B.C.; Balooch, M.

2004-01-01

The properties of femtosecond-pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or in a buffer gas using a Ti-sapphire laser with a 150 fs minimum pulse length. For in-vacuum deposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the average cluster size was approximately 7 nm for laser pulse lengths between 150 fs and 25 ps. The average cluster size dropped to approximately 1.5 nm at a pulse length of 500 ps. It was also observed that film thickness decreased with increasing laser pulse length. A reflective coating, which accumulated on the laser admission window during ablation, reduced the amount of laser energy reaching the target for subsequent laser shots and developed more rapidly at longer pulse lengths. This observation indicates that non-stoichiometric (metallic) ablatants were produced more readily at longer pulse lengths. The angular distribution of ejected material about the target normal was well fitted to a bi-cosine distribution of cos 47 θ+ cos 4 θ for ablation in vacuum using 150 fs pulses. XPS and AES revealed that the vacuum-deposited films contained excess amorphous Ga or As in addition to the stoichiometric GaAs nanocrystals seen with XRD. However, films containing only the GaAs nanocrystals were produced when ablation was carried out in the presence of a buffer gas with a pressure in excess of 6.67 Pa. At buffer gas pressure on the order of 1 Torr, it was found that the stoichiometry of the ablated target was also preserved. These experiments indicate that both laser pulse length and buffer gas pressure play important roles in the formation of multi-element nanocrystals by laser ablation. The effects of gas pressure on the target's morphology and the size of the GaAs nanocrystals formed will also be discussed

Automated dual-wavelength spectrophotometer optimized for phytochrome assay

International Nuclear Information System (INIS)

Pratt, L.H.; Wampler, J.E.; Rich, E.S. Jr.

1985-01-01

A microcomputer-controlled dual-wavelength spectrophotometer suitable for automated phytochrome assay is described. The optomechanical unit provides for sequential irradiation of the sample by the two measuring wavelengths with intervening dark intervals and for actinic irradiation to interconvert phytochrome between its two forms. Photomultiplier current is amplified, converted to a digital value and transferred into the computer using a custom-designed IEEE-488 bus interface. The microcomputer calculates mathematically both absorbance and absorbance difference values with dynamic correction for photomultiplier dark current. In addition, the computer controls the operating parameters of the spectrophotometer via a separate interface. These parameters include control of the durations of measuring and actinic irradiation intervals and their sequence. 14 references, 4 figures

On the influence of crystal size and wavelength on native SAD phasing.

Science.gov (United States)

Liebschner, Dorothee; Yamada, Yusuke; Matsugaki, Naohiro; Senda, Miki; Senda, Toshiya

2016-06-01

Native SAD is an emerging phasing technique that uses the anomalous signal of native heavy atoms to obtain crystallographic phases. The method does not require specific sample preparation to add anomalous scatterers, as the light atoms contained in the native sample are used as marker atoms. The most abundant anomalous scatterer used for native SAD, which is present in almost all proteins, is sulfur. However, the absorption edge of sulfur is at low energy (2.472 keV = 5.016 Å), which makes it challenging to carry out native SAD phasing experiments as most synchrotron beamlines are optimized for shorter wavelength ranges where the anomalous signal of sulfur is weak; for longer wavelengths, which produce larger anomalous differences, the absorption of X-rays by the sample, solvent, loop and surrounding medium (e.g. air) increases tremendously. Therefore, a compromise has to be found between measuring strong anomalous signal and minimizing absorption. It was thus hypothesized that shorter wavelengths should be used for large crystals and longer wavelengths for small crystals, but no thorough experimental analyses have been reported to date. To study the influence of crystal size and wavelength, native SAD experiments were carried out at different wavelengths (1.9 and 2.7 Å with a helium cone; 3.0 and 3.3 Å with a helium chamber) using lysozyme and ferredoxin reductase crystals of various sizes. For the tested crystals, the results suggest that larger sample sizes do not have a detrimental effect on native SAD data and that long wavelengths give a clear advantage with small samples compared with short wavelengths. The resolution dependency of substructure determination was analyzed and showed that high-symmetry crystals with small unit cells require higher resolution for the successful placement of heavy atoms.

Cavity optomechanics -- beyond the ground state

Science.gov (United States)

Meystre, Pierre

2011-05-01

The coupling of coherent optical systems to micromechanical devices, combined with breakthroughs in nanofabrication and in ultracold science, has opened up the exciting new field of cavity optomechanics. Cooling of the vibrational motion of a broad range on oscillating cantilevers and mirrors near their ground state has been demonstrated, and the ground state of at least one such system has now been reached. Cavity optomechanics offers much promise in addressing fundamental physics questions and in applications such as the detection of feeble forces and fields, or the coherent control of AMO systems and of nanoscale electromechanical devices. However, these applications require taking cavity optomechanics ``beyond the ground state.'' This includes the generation and detection of squeezed and other non-classical states, the transfer of squeezing between electromagnetic fields and motional quadratures, and the development of measurement schemes for the characterization of nanomechanical structures. The talk will present recent ``beyond ground state'' developments in cavity optomechanics. We will show how the magnetic coupling between a mechanical membrane and a BEC - or between a mechanical tuning fork and a nanoscale cantilever - permits to control and monitor the center-of-mass position of the mechanical system, and will comment on the measurement back-action on the membrane motion. We will also discuss of state transfer between optical and microwave fields and micromechanical devices. Work done in collaboration with Dan Goldbaum, Greg Phelps, Keith Schwab, Swati Singh, Steve Steinke, Mehmet Tesgin, and Mukund Vengallatore and supported by ARO, DARPA, NSF, and ONR.

Quantum noise spectra for periodically driven cavity optomechanics

Science.gov (United States)

Aranas, E. B.; Akram, M. Javed; Malz, Daniel; Monteiro, T. S.

2017-12-01

A growing number of experimental setups in cavity optomechanics exploit periodically driven fields. However, such setups are not amenable to analysis by using simple, yet powerful, closed-form expressions of linearized optomechanics, which have provided so much of our present understanding of experimental optomechanics. In the present paper, we formulate a method to calculate quantum noise spectra in modulated optomechanical systems, which we analyze, compare, and discuss with two other recently proposed solutions: we term these (i) frequency-shifted operators, (ii) Floquet [Phys. Rev. A 94, 023803 (2016), 10.1103/PhysRevA.94.023803], and (iii) iterative analysis [New J. Phys. 18, 113021 (2016), 10.1088/1367-2630/18/11/113021]. We prove that (i) and (ii) yield equivalent noise spectra and find that (iii) is an analytical approximation to (i) for weak modulations. We calculate the noise spectra of a doubly modulated system describing experiments of levitated particles in hybrid electro-optical traps. We show excellent agreement with Langevin stochastic simulations in the thermal regime and predict squeezing in the quantum regime. Finally, we reveal how otherwise-inaccessible spectral components of a modulated system can be measured in heterodyne detection through an appropriate choice of modulation frequencies.

Optomechanical entanglement via non-degenerate parametric interactions

Science.gov (United States)

Ahmed, Rizwan; Qamar, Shahid

2017-10-01

We present a scheme for the optomechanical entanglement between a micro-mechanical mirror and the field inside a bimodal cavity system using a non-degenerate optical parametric amplifier (NOPA). Our results show that the introduction of NOPA makes the entanglement stronger or more robust against the mean number of average thermal phonons and cavity decay. Interestingly, macroscopic entanglement depends upon the choice of the phase associated with classical field driving NOPA. We also consider the effects of input laser power on optomechanical entanglement.

Tunable two-photon correlation in a double-cavity optomechanical system

Directory of Open Access Journals (Sweden)

Zhi-Bo Feng

2015-12-01

Full Text Available Correlated photons are essential sources for quantum information processing. We propose a practical scheme to generate pairs of correlated photons in a controllable fashion from a double-cavity optomechanical system, where the variable optomechanical coupling strength makes it possible to tune the photon correlation at our will. The key operation is based on the repulsive or attractive interaction between the two photons intermediated by the mechanical resonator. The present protocol could provide a potential approach to coherent control of the photon correlation using the optomechanical cavity.

Optomechanically induced transparency with Bose–Einstein condensate in double-cavity optomechanical system

Science.gov (United States)

Liu, Li-Wei; Gengzang, Duo-Jie; An, Xiu-Jia; Wang, Pei-Yu

2018-03-01

We propose a novel technique of generating multiple optomechanically induced transparency (OMIT) of a weak probe field in hybrid optomechanical system. This system consists of a cigar-shaped Bose–Einstein condensate (BEC), trapped inside each high finesse Fabry-Pérot cavity. In the resolved sideband regime, the analytic solutions of the absorption and the dispersion spectrum are given. The tunneling strength of the two resonators and the coupling parameters of the each BEC in combination with the cavity field have the appearance of three distinct OMIT windows in the absorption spectrum. Furthermore, whether there is BEC in each cavity is a key factor in the number of OMIT windows determination. The technique presented may have potential applications in quantum engineering and quantum information networks. Project supported by the National Natural Science Foundation of China (Grant Nos. 11564034, 11105062, and 21663026) and the Scientific Research Funds of College of Electrical Engineering, Northwest University, China (Grant No. xbmuyjrc201115).

Mode competition and hopping in optomechanical nano-oscillators

Science.gov (United States)

Zhang, Xingwang; Lin, Tong; Tian, Feng; Du, Han; Zou, Yongchao; Chau, Fook Siong; Zhou, Guangya

2018-04-01

We investigate the inter-mode nonlinear interaction in the multi-mode optomechanical nano-oscillator which consists of coupled silicon nanocantilevers, where the integrated photonic crystal nanocavities provide the coupling between the optical and mechanical modes. Due to the self-saturation and cross-saturation of the mechanical gain, the inter-mode competition is observed, which leads to the bistable operation of the optomechanical nano-oscillator: only one of the mechanical modes can oscillate at any one time, and the oscillation of one mode extremely suppresses that of the other with a side mode suppression ratio (SMSR) up to 40 dB. In the meantime, mode hopping, i.e., the optomechanical oscillation switches from one mode to the other, is also observed and found to be able to be provoked by excitation laser fluctuations.

Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111)A substrates

Energy Technology Data Exchange (ETDEWEB)

Galiev, G. B.; Klimov, E. A. [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation); Vasiliev, A. L.; Imamov, R. M. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” (Russian Federation); Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation); Trunkin, I. N. [National Research Centre “Kurchatov Institute” (Russian Federation); Maltsev, P. P. [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation)

2017-01-15

The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111)A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in “low-temperature” GaAs serve as formation centers of arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100–150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111)A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150–200 nm.

Optomechanical entanglement via non-degenerate parametric interactions

International Nuclear Information System (INIS)

Ahmed, Rizwan; Qamar, Shahid

2017-01-01

We present a scheme for the optomechanical entanglement between a micro-mechanical mirror and the field inside a bimodal cavity system using a non-degenerate optical parametric amplifier (NOPA). Our results show that the introduction of NOPA makes the entanglement stronger or more robust against the mean number of average thermal phonons and cavity decay. Interestingly, macroscopic entanglement depends upon the choice of the phase associated with classical field driving NOPA. We also consider the effects of input laser power on optomechanical entanglement. (paper)

Optimal control of the power adiabatic stroke of an optomechanical heat engine.

Science.gov (United States)

Bathaee, M; Bahrampour, A R

2016-08-01

We consider the power adiabatic stroke of the Otto optomechanical heat engine introduced in Phys. Rev. Lett. 112, 150602 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.150602. We derive the maximum extractable work of both optomechanical normal modes in the minimum time while the system experiences quantum friction effects. We show that the total work done by the system in the power adiabatic stroke is optimized by a bang-bang control. The time duration of the power adiabatic stroke is of the order of the inverse of the effective optomechanical-coupling coefficient. The optimal phase-space trajectory of the Otto cycle for both optomechanical normal modes is also obtained.

Paths to light trapping in thin film GaAs solar cells.

Science.gov (United States)

Xiao, Jianling; Fang, Hanlin; Su, Rongbin; Li, Kezheng; Song, Jindong; Krauss, Thomas F; Li, Juntao; Martins, Emiliano R

2018-03-19

It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

Steady-state entanglement activation in optomechanical cavities

Science.gov (United States)

Farace, Alessandro; Ciccarello, Francesco; Fazio, Rosario; Giovannetti, Vittorio

2014-02-01

Quantum discord, and related indicators, are raising a relentless interest as a novel paradigm of nonclassical correlations beyond entanglement. Here, we discover a discord-activated mechanism yielding steady-state entanglement production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.

The GAAS Metagenomic Tool and Its Estimations of Viral and Microbial Average Genome Size in Four Major Biomes

OpenAIRE

Angly, Florent E.; Willner, Dana; Prieto-Dav?, Alejandra; Edwards, Robert A.; Schmieder, Robert; Vega-Thurber, Rebecca; Antonopoulos, Dionysios A.; Barott, Katie; Cottrell, Matthew T.; Desnues, Christelle; Dinsdale, Elizabeth A.; Furlan, Mike; Haynes, Matthew; Henn, Matthew R.; Hu, Yongfei

2009-01-01

Metagenomic studies characterize both the composition and diversity of uncultured viral and microbial communities. BLAST-based comparisons have typically been used for such analyses; however, sampling biases, high percentages of unknown sequences, and the use of arbitrary thresholds to find significant similarities can decrease the accuracy and validity of estimates. Here, we present Genome relative Abundance and Average Size (GAAS), a complete software package that provides improved estimate...

Experimental studies of the charge limit phenomenon in NEA GaAs photocathodes

International Nuclear Information System (INIS)

Tang, H.; Alley, R.K.; Aoyagi, H.; Clendenin, J.E.; Frisch, J.C.; Mulhollan, G.A.; Saez, P.J.; Schultz, D.C.; Turner, J.L.

1994-06-01

Negative electron affinity GaAs photocathodes have been in continuous use at SLAC for generating polarized electron beams since early 1992. If the quantum efficiency of a GaAs cathode is below a critical value, the maximum photoemitted charge with photons of energies close to the band gap in a 2-ns pulse is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this novel charge limit phenomenon in a variety of GaAs photocathodes of different structures and doping densities. We find that the charge limit is strongly dependent on the cathode's quantum efficiency and the extraction electric field, and to a lesser degree on the excitation laser wavelength. In addition, we show that the temporal behavior of the charge limit depends critically on the doping density

Controllable chaos in hybrid electro-optomechanical systems

Science.gov (United States)

Wang, Mei; Lü, Xin-You; Ma, Jin-Yong; Xiong, Hao; Si, Liu-Gang; Wu, Ying

2016-01-01

We investigate the nonlinear dynamics of a hybrid electro-optomechanical system (EOMS) that allows us to realize the controllable opto-mechanical nonlinearity by driving the microwave LC resonator with a tunable electric field. A controllable optical chaos is realized even without changing the optical pumping. The threshold and lifetime of the chaos could be optimized by adjusting the strength, frequency, or phase of the electric field. This study provides a method of manipulating optical chaos with an electric field. It may offer the prospect of exploring the controllable chaos in on-chip optoelectronic devices and its applications in secret communication. PMID:26948505

Controllable chaos in hybrid electro-optomechanical systems.

Science.gov (United States)

Wang, Mei; Lü, Xin-You; Ma, Jin-Yong; Xiong, Hao; Si, Liu-Gang; Wu, Ying

2016-03-07

We investigate the nonlinear dynamics of a hybrid electro-optomechanical system (EOMS) that allows us to realize the controllable opto-mechanical nonlinearity by driving the microwave LC resonator with a tunable electric field. A controllable optical chaos is realized even without changing the optical pumping. The threshold and lifetime of the chaos could be optimized by adjusting the strength, frequency, or phase of the electric field. This study provides a method of manipulating optical chaos with an electric field. It may offer the prospect of exploring the controllable chaos in on-chip optoelectronic devices and its applications in secret communication.

Controllable nonlinearity in a dual-coupling optomechanical system under a weak-coupling regime

Science.gov (United States)

Zhu, Gui-Lei; Lü, Xin-You; Wan, Liang-Liang; Yin, Tai-Shuang; Bin, Qian; Wu, Ying

2018-03-01

Strong quantum nonlinearity gives rise to many interesting quantum effects and has wide applications in quantum physics. Here we investigate the quantum nonlinear effect of an optomechanical system (OMS) consisting of both linear and quadratic coupling. Interestingly, a controllable optomechanical nonlinearity is obtained by applying a driving laser into the cavity. This controllable optomechanical nonlinearity can be enhanced into a strong coupling regime, even if the system is initially in the weak-coupling regime. Moreover, the system dissipation can be suppressed effectively, which allows the appearance of phonon sideband and photon blockade effects in the weak-coupling regime. This work may inspire the exploration of a dual-coupling optomechanical system as well as its applications in modern quantum science.

Review of cavity optomechanical cooling

International Nuclear Information System (INIS)

Liu Yong-Chun; Hu Yu-Wen; Xiao Yun-Feng; Wong Chee Wei

2013-01-01

Quantum manipulation of macroscopic mechanical systems is of great interest in both fundamental physics and applications ranging from high-precision metrology to quantum information processing. For these purposes, a crucial step is to cool the mechanical system to its quantum ground state. In this review, we focus on the cavity optomechanical cooling, which exploits the cavity enhanced interaction between optical field and mechanical motion to reduce the thermal noise. Recent remarkable theoretical and experimental efforts in this field have taken a major step forward in preparing the motional quantum ground state of mesoscopic mechanical systems. This review first describes the quantum theory of cavity optomechanical cooling, including quantum noise approach and covariance approach; then, the up-to-date experimental progresses are introduced. Finally, new cooling approaches are discussed along the directions of cooling in the strong coupling regime and cooling beyond the resolved sideband limit. (topical review - quantum information)

Electrons, holes, and excitons in GaAs polytype quantum dots

Energy Technology Data Exchange (ETDEWEB)

Climente, Juan I.; Segarra, Carlos; Rajadell, Fernando; Planelles, Josep, E-mail: josep.planelles@uji.es [Departament de Química Física i Analítica, Universitat Jaume I, E-12080 Castelló (Spain)

2016-03-28

Single and multi-band k⋅p Hamiltonians for GaAs crystal phase quantum dots are used to assess ongoing experimental activity on the role of such factors as quantum confinement, spontaneous polarization, valence band mixing, and exciton Coulomb interaction. Spontaneous polarization is found to be a dominating term. Together with the control of dot thickness [Vainorius et al., Nano Lett. 15, 2652 (2015)], it enables wide exciton wavelength and lifetime tunability. Several new phenomena are predicted for small diameter dots [Loitsch et al., Adv. Mater. 27, 2195 (2015)], including non-heavy hole ground state, strong hole spin admixture, and a type-II to type-I exciton transition, which can be used to improve the absorption strength and reduce the radiative lifetime of GaAs polytypes.

Optical tristability in a hybrid optomechanical system

Science.gov (United States)

Asghari Nejad, A.; Askari, H. R.; Baghshahi, H. R.

2018-05-01

In this paper, we investigate a hybrid optomechanical system consisting of two cavities, which one of them is an optomechanical cavity that includes an optical parametric amplifier (OPA) and the other is a traditional cavity which contains an atomic medium. Hamiltonian of the system is written in a rotating frame with a rotation frequency of the frequency of input field to the system. Using Heisenberg-Langevin equations of motion, the dynamics of the system is described. Applying the steady-state conditions leads to a system of equations of the mean values of the operators of the system. The stability condition of the system is satisfied numerically and behavior of optomechanical cavity is investigated in different situations to find the effect of changing of the parameters of the system on the type of its stability. We show proposed system has the capability of tristable behavior, where, the gain coefficient of OPA acts as a switch in changing the bistability of the system to a tristable manner. The building block of the tristability in this system can be figured out as the enhanced nonlinearity of the system due to the presence of OPA.

A microelectromechanically controlled cavity optomechanical sensing system

International Nuclear Information System (INIS)

Miao Houxun; Srinivasan, Kartik; Aksyuk, Vladimir

2012-01-01

Microelectromechanical systems (MEMS) have been applied to many measurement problems in physics, chemistry, biology and medicine. In parallel, cavity optomechanical systems have achieved quantum-limited displacement sensitivity and ground state cooling of nanoscale objects. By integrating a novel cavity optomechanical structure into an actuated MEMS sensing platform, we demonstrate a system with high-quality-factor interferometric readout, electrical tuning of the optomechanical coupling by two orders of magnitude and a mechanical transfer function adjustable via feedback. The platform separates optical and mechanical components, allowing flexible customization for specific scientific and commercial applications. We achieve a displacement sensitivity of 4.6 fm Hz -1/2 and a force sensitivity of 53 aN Hz -1/2 with only 250 nW optical power launched into the sensor. Cold-damping feedback is used to reduce the thermal mechanical vibration of the sensor by three orders of magnitude and to broaden the sensor bandwidth by approximately the same factor, to above twice the fundamental frequency of ≈40 kHz. The readout sensitivity approaching the standard quantum limit is combined with MEMS actuation in a fully integrated, compact, low-power, stable system compatible with Si batch fabrication and electronics integration. (paper)

Present opto-mechanical design status of NFIRAOS

Science.gov (United States)

Byrnes, Peter W. G.; Atwood, Jenny; Boucher, Marc-André; Fitzsimmons, Joeleff; Hill, Alexis; Herriot, Glen; Spanò, Paolo; Szeto, Kei; Wevers, Ivan

2014-07-01

This paper describes the current opto-mechanical design of NFIRAOS (Narrow Field InfraRed Adaptive Optics System) for the Thirty Meter Telescope (TMT). The preliminary design update review for NFIRAOS was successfully held in December 2011, and incremental design progress has since occurred on several fronts. The majority of NFIRAOS is housed within an insulated and cooled enclosure, and operates at -30 C to reduce background emissivity. The cold optomechanics are attached to a space-frame structure, kinematically supported by bipods that penetrate the insulated enclosure. The bipods are attached to an exo-structure at ambient temperature, which also supports up to three client science instruments and a science calibration unit.

Optomechanical design of TMT NFIRAOS Subsystems at INO

Science.gov (United States)

Lamontagne, Frédéric; Desnoyers, Nichola; Grenier, Martin; Cottin, Pierre; Leclerc, Mélanie; Martin, Olivier; Buteau-Vaillancourt, Louis; Boucher, Marc-André; Nash, Reston; Lardière, Olivier; Andersen, David; Atwood, Jenny; Hill, Alexis; Byrnes, Peter W. G.; Herriot, Glen; Fitzsimmons, Joeleff; Véran, Jean-Pierre

2017-08-01

The adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). Recently, INO has been involved in the optomechanical design of several subsystems of NFIRAOS, including the Instrument Selection Mirror (ISM), the NFIRAOS Beamsplitters (NBS), and the NFIRAOS Source Simulator system (NSS) comprising the Focal Plane Mask (FPM), the Laser Guide Star (LGS) sources, and the Natural Guide Star (NGS) sources. This paper presents an overview of these subsystems and the optomechanical design approaches used to meet the optical performance requirements under environmental constraints.

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

Science.gov (United States)

Liu, Ling; Onck, Patrick R.

2017-08-01

Azobenzene-embedded liquid crystal polymers can undergo mechanical deformation in response to ultraviolet (UV) light. The natural rodlike trans state azobenzene absorbs UV light and isomerizes to a bentlike cis state, which disturbs the order of the polymer network, leading to an anisotropic deformation. The current consensus is that the magnitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [Liu and Broer, Nat. Commun. 6 8334 (2015)., 10.1038/ncomms9334] shows that a drastic (fourfold) increase of the photoinduced deformation can be generated by exposing the samples simultaneously to 365 nm (UV) and 455 nm (visible) light. To elucidate the physical mechanism that drives this increase, we develop a two-light attenuation model and an optomechanical constitutive relation that not only accounts for the statistical accumulation of cis azobenzenes, but also for the dynamic trans-cis-trans oscillatory isomerization process. Our experimentally calibrated model predicts that the optimal single-wavelength exposure is 395 nm light, a pronounced shift towards the visible spectrum. In addition, we identify a range of optimal combinations of two-wavelength lights that generate a favorable response for a given amount of injected energy. Our model provides mechanistic insight into the different (multi)wavelength exposures used in experiments and, at the same time, opens new avenues towards enhanced, multiwavelength optomechanical behavior.

Quadratic measurement and conditional state preparation in an optomechanical system

DEFF Research Database (Denmark)

A. Brawley, George; Vanner, Michael A.; Bowen, Warwick P.

2014-01-01

We experimentally demonstrate, for the first time, quadratic measurement of mechanical motion in an optomechanical system. We use this nonlinear easurement to conditionally prepare classical non-Gaussian states of motion of a micro-mechanical oscillator.......We experimentally demonstrate, for the first time, quadratic measurement of mechanical motion in an optomechanical system. We use this nonlinear easurement to conditionally prepare classical non-Gaussian states of motion of a micro-mechanical oscillator....

Structural and optical properties of vapor-etched porous GaAs

Energy Technology Data Exchange (ETDEWEB)

Smida, A.; Laatar, F. [Photovoltaic Laboratory, Centre for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Hassen, M., E-mail: mhdhassen@yahoo.fr [Photovoltaic Laboratory, Centre for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Higher Institute of Applied Science and Technology of Sousse, City Taffala (Ibn Khaldun), 4003 Sousse (Tunisia); Ezzaouia, H. [Photovoltaic Laboratory, Centre for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia)

2016-08-15

This paper consists to present first results concerning the structure of porous GaAs layer (por-GaAs-L) prepared by using HF/HNO{sub 3} as acidic solution in vapor etching (VE) method. In order to clarify this method, we detail here its principle and explain how por-GaAs-Ls are formed, taking into account the influencing of the exposure time of the GaAs substrate to the acid vapor. The etched GaAs layers have been investigated by UV–visible and PL analysis. One porous layer was performed to be characterised by Atomic Force Microscopy (AFM), FTIR spectroscopy, and X-Ray Diffraction (XRD). The porous structure was constituted by a nanocrystals with an average size about 6 nm. These nanocrystals were calculated from XRD peak using Scherrer's formula, AFM imaging, and also by using effective mass approximation model from effective band gap. - Highlights: • Porous GaAs layer was prepared by using Vapor etching (VE) method. • Effect of VE duration on the microstructural optical properties of the GaAs substrate • Porous structure of GaAs layer was demonstrated by using SEM and AFM microscopy.

Structural and optical properties of vapor-etched porous GaAs

International Nuclear Information System (INIS)

Smida, A.; Laatar, F.; Hassen, M.; Ezzaouia, H.

2016-01-01

This paper consists to present first results concerning the structure of porous GaAs layer (por-GaAs-L) prepared by using HF/HNO 3 as acidic solution in vapor etching (VE) method. In order to clarify this method, we detail here its principle and explain how por-GaAs-Ls are formed, taking into account the influencing of the exposure time of the GaAs substrate to the acid vapor. The etched GaAs layers have been investigated by UV–visible and PL analysis. One porous layer was performed to be characterised by Atomic Force Microscopy (AFM), FTIR spectroscopy, and X-Ray Diffraction (XRD). The porous structure was constituted by a nanocrystals with an average size about 6 nm. These nanocrystals were calculated from XRD peak using Scherrer's formula, AFM imaging, and also by using effective mass approximation model from effective band gap. - Highlights: • Porous GaAs layer was prepared by using Vapor etching (VE) method. • Effect of VE duration on the microstructural optical properties of the GaAs substrate • Porous structure of GaAs layer was demonstrated by using SEM and AFM microscopy.

Molecular cavity optomechanics as a theory of plasmon-enhanced Raman scattering.

Science.gov (United States)

Roelli, Philippe; Galland, Christophe; Piro, Nicolas; Kippenberg, Tobias J

2016-02-01

The exceptional enhancement of Raman scattering by localized plasmonic resonances in the near field of metallic nanoparticles, surfaces or tips (SERS, TERS) has enabled spectroscopic fingerprinting down to the single molecule level. The conventional explanation attributes the enhancement to the subwavelength confinement of the electromagnetic field near nanoantennas. Here, we introduce a new model that also accounts for the dynamical nature of the plasmon-molecule interaction. We thereby reveal an enhancement mechanism not considered before: dynamical backaction amplification of molecular vibrations. We first map the system onto the canonical Hamiltonian of cavity optomechanics, in which the molecular vibration and the plasmon are parametrically coupled. We express the vacuum optomechanical coupling rate for individual molecules in plasmonic 'hot-spots' in terms of the vibrational mode's Raman activity and find it to be orders of magnitude larger than for microfabricated optomechanical systems. Remarkably, the frequency of commonly studied molecular vibrations can be comparable to or larger than the plasmon's decay rate. Together, these considerations predict that an excitation laser blue-detuned from the plasmon resonance can parametrically amplify the molecular vibration, leading to a nonlinear enhancement of Raman emission that is not predicted by the conventional theory. Our optomechanical approach recovers known results, provides a quantitative framework for the calculation of cross-sections, and enables the design of novel systems that leverage dynamical backaction to achieve additional, mode-selective enhancements. It also provides a quantum mechanical framework to analyse plasmon-vibrational interactions in terms of molecular quantum optomechanics.

Ab initio structural and vibrational properties of GaAs diamondoids and nanocrystals

Directory of Open Access Journals (Sweden)

Mudar Ahmed Abdulsattar

2014-12-01

Full Text Available Gallium arsenide diamondoids structural and vibrational properties are investigated using density functional theory at the PBE/6-31(d level and basis including polarization functions. Variation of energy gap as these diamondoids increase in size is seen to follow confinement theory for diamondoids having nearly equiaxed dimensions. Density of energy states transforms from nearly single levels to band structure as we reach larger diamondoids. Bonds of surface hydrogen with As atoms are relatively localized and shorter than that bonded to Ga atoms. Ga-As bonds have a distribution range of values due to surface reconstruction and effect of bonding to hydrogen atoms. Experimental bulk Ga-As bond length (2.45 Å is within this distribution range. Tetrahedral and dihedral angles approach values of bulk as we go to higher diamondoids. Optical-phonon energy of larger diamondoids stabilizes at 0.037 eV (297 cm-1 compared to experimental 0.035 eV (285.2 cm-1. Ga-As force constant reaches 1.7 mDyne/Å which is comparable to Ga-Ge force constant (1.74 mDyne/Å. Hydrogen related vibrations are nearly constant and serve as a fingerprint of GaAs diamondoids while Ga-As vibrations vary with size of diamondoids.

A chip-scale integrated cavity-electro-optomechanics platform.

Science.gov (United States)

Winger, M; Blasius, T D; Mayer Alegre, T P; Safavi-Naeini, A H; Meenehan, S; Cohen, J; Stobbe, S; Painter, O

2011-12-05

We present an integrated optomechanical and electromechanical nanocavity, in which a common mechanical degree of freedom is coupled to an ultrahigh-Q photonic crystal defect cavity and an electrical circuit. The system allows for wide-range, fast electrical tuning of the optical nanocavity resonances, and for electrical control of optical radiation pressure back-action effects such as mechanical amplification (phonon lasing), cooling, and stiffening. These sort of integrated devices offer a new means to efficiently interconvert weak microwave and optical signals, and are expected to pave the way for a new class of micro-sensors utilizing optomechanical back-action for thermal noise reduction and low-noise optical read-out.

Ultralow-Noise SiN Trampoline Resonators for Sensing and Optomechanics

Science.gov (United States)

Reinhardt, Christoph; Müller, Tina; Bourassa, Alexandre; Sankey, Jack C.

2016-04-01

In force sensing, optomechanics, and quantum motion experiments, it is typically advantageous to create lightweight, compliant mechanical elements with the lowest possible force noise. Here, we report the fabrication and characterization of high-aspect-ratio, nanogram-scale Si3 N4 "trampolines" having quality factors above 4 ×107 and ringdown times exceeding 5 min (mHz linewidth). These devices exhibit thermally limited force noise sensitivities below 20 aN /Hz1 /2 at room temperature, which is the lowest among solid-state mechanical sensors. We also characterize the suitability of these devices for high-finesse cavity readout and optomechanics applications, finding no evidence of surface or bulk optical losses from the processed nitride in a cavity achieving finesse 40,000. These parameters provide access to a single-photon cooperativity C0˜8 in the resolved-sideband limit, wherein a variety of outstanding optomechanics goals become feasible.

Formation of columnar (In,Ga)As quantum dots on GaAs(100)

International Nuclear Information System (INIS)

He, J.; Noetzel, R.; Offermans, P.; Koenraad, P.M.; Gong, Q.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

2004-01-01

Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs/InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced

Optomechanical stability design of space optical mapping camera

Science.gov (United States)

Li, Fuqiang; Cai, Weijun; Zhang, Fengqin; Li, Na; Fan, Junjie

2018-01-01

According to the interior orientation elements and imaging quality requirements of mapping application to mapping camera and combined with off-axis three-mirror anastigmat(TMA) system, high optomechanical stability design of a space optical mapping camera is introduced in this paper. The configuration is a coaxial TMA system used in off-axis situation. Firstly, the overall optical arrangement is described., and an overview of the optomechanical packaging is provided. Zerodurglass, carbon fiber composite and carbon-fiber reinforced silicon carbon (C/SiC) are widely used in the optomechanical structure, because their low coefficient of thermal expansion (CTE) can reduce the thermal sensitivity of the mirrors and focal plane. Flexible and unloading support are used in reflector and camera supporting structure. Epoxy structural adhesives is used for bonding optics to metal structure is also introduced in this paper. The primary mirror is mounted by means of three-point ball joint flexures system, which is attach to the back of the mirror. Then, In order to predict flexural displacements due to gravity, static finite element analysis (FEA) is performed on the primary mirror. The optical performance peak-to-valley (PV) and root-mean-square (RMS) wavefront errors are detected before and after assemble. Also, the dynamic finite element analysis(FEA) of the whole optical arrangement is carried out as to investigate the performance of optomechanical. Finally, in order to evaluate the stability of the design, the thermal vacuum test and vibration test are carried out and the Modulation Transfer Function (MTF) and elements of interior orientation are presented as the evaluation index. Before and after the thermal vacuum test and vibration test, the MTF, focal distance and position of the principal point of optical system are measured and the result is as expected.

Controllable growth and optical properties of InP and InP/InAs nanostructures on the sidewalls of GaAs nanowires

International Nuclear Information System (INIS)

Yan, Xin; Zhang, Xia; Li, Junshuai; Cui, Jiangong; Ren, Xiaomin

2014-01-01

The growth and optical properties of InP and InP/InAs nanostructures on GaAs nanowires are investigated. InP quantum well and quantum dots (QDs) are formed on the sidewalls of GaAs nanowires successively with increasing the deposition time of InP. The GaAs/InP nanowire heterostructure exhibits a type-II band alignment. The wavelength of the InP quantum well is in the range of 857–892 nm at 77 K, which means that the quantum well is nearly fully strained. The InP quantum dot, which has a bow-shaped cross section, exhibits dislocation-free pure zinc blende structure. Stranski-Krastanow InAs quantum dots are subsequently formed on the GaAs/InP nanowire core-shell structure. The InAs quantum dots are distributed over the middle part of the nanowire, indicating that the In atoms contributing to the quantum dots mainly come from the vapor rather than the substrate. The longest emission wavelength obtained from the InAs QDs is 1039 nm at 77 K. The linewidth is as narrow as 46.3 meV, which is much narrower than those on planar InP substrates and wurtzite InP nanowires, suggesting high-crystal-quality, phase-purity, and size-uniformity of quantum dots

Optical-response properties in an atom-assisted optomechanical system with a mechanical pump

Science.gov (United States)

Sun, Xue-Jian; Chen, Hao; Liu, Wen-Xiao; Li, Hong-Rong

2017-05-01

We investigate the optical-response properties of a coherent-mechanical pumped optomechanical system (OMS) coupled to a Λ-type three-level atomic ensemble. Due to the optomechanical and the cavity-atom couplings, the optomechanically induced transparency (OMIT) and electromagnetically induced transparency (EIT) phenomena could both be observed from our proposal. In the presence of a coherent mechanical pump, we show that the OMIT behavior of the probe field exhibits a phase-dependent effect, leading to the switch from OMIT to optomechanically induced absorption or amplification, while the feature of EIT remains unchanged. The distinctly different effects of the mechanical pump on OMIT and EIT behavior assure us that the absorption (amplification) and transparency of the output probe field can be simultaneously observed. Moreover, a tunable switch from slow to fast light can also be realized by tuning the phase and amplitude of the mechanical pump. In particular, the presence of the atomic ensemble can further adjust the group delay, providing additional flexibility for achieving the tunable switch.

Levitated optomechanics with a fiber Fabry-Perot interferometer

Science.gov (United States)

Pontin, A.; Mourounas, L. S.; Geraci, A. A.; Barker, P. F.

2018-02-01

In recent years, quantum phenomena have been experimentally demonstrated on variety of optomechanical systems ranging from micro-oscillators to photonic crystals. Since single photon couplings are quite small, most experimental approaches rely on the realization of high finesse Fabry-Perot cavities in order to enhance the effective coupling. Here we show that by exploiting a, long path, low finesse fiber Fabry-Perot interferometer ground state cooling can be achieved. We model a 100 m long cavity with a finesse of 10 and analyze the impact of additional noise sources arising from the fiber. As a mechanical oscillator we consider a levitated microdisk but the same approach could be applied to other optomechanical systems.

Ultralow-Noise SiN Trampoline Resonators for Sensing and Optomechanics

Directory of Open Access Journals (Sweden)

Christoph Reinhardt

2016-04-01

Full Text Available In force sensing, optomechanics, and quantum motion experiments, it is typically advantageous to create lightweight, compliant mechanical elements with the lowest possible force noise. Here, we report the fabrication and characterization of high-aspect-ratio, nanogram-scale Si_{3}N_{4} “trampolines” having quality factors above 4×10^{7} and ringdown times exceeding 5 min (mHz linewidth. These devices exhibit thermally limited force noise sensitivities below 20  aN/Hz^{1/2} at room temperature, which is the lowest among solid-state mechanical sensors. We also characterize the suitability of these devices for high-finesse cavity readout and optomechanics applications, finding no evidence of surface or bulk optical losses from the processed nitride in a cavity achieving finesse 40,000. These parameters provide access to a single-photon cooperativity C_{0}∼8 in the resolved-sideband limit, wherein a variety of outstanding optomechanics goals become feasible.

Injection locking of optomechanical oscillators via acoustic waves.

Science.gov (United States)

Huang, Ke; Hossein-Zadeh, Mani

2018-04-02

Injection locking is an effective technique for synchronization of oscillator networks and controlling the phase and frequency of individual oscillators. As such, exploring new mechanisms for injection locking of emerging oscillators is important for their usage in various systems. Here, we present the first demonstration of injection locking of a radiation pressure driven optomechanical oscillator (OMO) via acoustic waves. As opposed to previously reported techniques (based on pump modulation or direct application of a modulated electrostatic force), injection locking of OMO via acoustic waves does not require optical power modulation or physical contact with the OMO and it can be easily implemented on various platforms to lock different types of OMOs independent of their size and structure. Using this approach we have locked the phase and frequency of two distinct modes of a microtoroidal silica OMO to a piezoelectric transducer (PZT). We have characterized the behavior of the injection locked OMO with three acoustic excitation configurations and showed that even without proper acoustic impedance, matching the OMO can be locked to the PZT and tuned over 17 kHz with only -30 dBm of RF power fed to the PZT. The high efficiency, simplicity, and scalability of the proposed approach paves the road toward a new class of photonic systems that rely on synchronization of several OMOs to a single or multiple RF oscillators with applications in optical communication, metrology, and sensing. Beyond its practical applications, injection locking via acoustic waves can be used in fundamental studies in quantum optomechanics where thermal and optical isolation of the OMO are critical.

Bathed, Strained, Attenuated, Annihilated: Towards Quantum Optomechanics

Science.gov (United States)

Pepper, Brian Jeffrey

The field of optomechanics studies tiny devices that can be pushed mechanically by light. It is an extremely promising avenue towards tests of quantum mechanics on a macroscopic scale, by transferring quantum states of light to nano- or micromechanical objects. This dissertation concerns a long term research program to create quantum superpositions of a macroscopic mirror in an optomechanical cavity. This dissertation has two broad thrusts. The first focuses on microfabrication of a new type of device called optomechanical trampoline resonators, consisting of a small mirror on a cross-shaped tensed silicon nitride membrane. Devices have been fabricated with high mechanical and optical quality, including a 300 kHz device with quality factor 480,000, as well as a device of optical finesse 107,000. These devices are well into the sideband-resolved regime and suitable for optical cooling to the quantum ground state. One such device has been optically cooled to approximately 10 phonons. The second major thrust is theoretical. Creating a macroscopic superposition is a challenging problem, requiring optical cooling to the ground state, strong coupling, extremely high optical finesse and extremely low frequency. A realistic assessment of achievable parameters indicates that it is possible to achieve ground state cooling or strong coupling, but not both. This dissertation proposes a new technique using postselection to achieve macroscopic superpositions with only weak coupling. This relaxes some of the required parameters by orders of magnitude. Prospects for observing hypothetical novel decoherence mechanisms are also discussed.

Improvements of MCT MBE Growth on GaAs

Science.gov (United States)

Ziegler, J.; Wenisch, J.; Breiter, R.; Eich, D.; Figgemeier, H.; Fries, P.; Lutz, H.; Wollrab, R.

2014-08-01

In recent years, continuous progress has been published in the development of HgCdTe (MCT) infrared (IR) focal plane arrays (FPAs) fabricated by molecular beam epitaxy on GaAs substrates. In this publication, further characterization of the state-of-the art 1280 × 1024 pixel, 15- μm pitch detector fabricated from this material in both the mid-wavelength (MWIR) and long-wavelength (LWIR) IR region will be presented. For MWIR FPAs, the percentage of defective pixel remains below 0.5% up to an operating temperature ( T OP) of around 100 K. For the LWIR FPA, an operability of 99.25% was achieved for a T OP of 76 K. Additionally, the beneficial effect of the inclusion of MCT layers with a graded composition region was investigated and demonstrated on current-voltage ( IV) characteristics on test diodes in a MWIR FPA.

Macroscopic quantum mechanics: theory and experimental concepts of optomechanics

International Nuclear Information System (INIS)

Chen Yanbei

2013-01-01

Rapid experimental progress has recently allowed the use of light to prepare macroscopic mechanical objects into nearly pure quantum states. This research field of quantum optomechanics opens new doors towards testing quantum mechanics, and possibly other laws of physics, in new regimes. In the first part of this article, I will review a set of techniques of quantum measurement theory that are often used to analyse quantum optomechanical systems. Some of these techniques were originally designed to analyse how a classical driving force passes through a quantum system, and can eventually be detected with an optimal signal-to-noise ratio—while others focus more on the quantum-state evolution of a mechanical object under continuous monitoring. In the second part of this article, I will review a set of experimental concepts that will demonstrate quantum mechanical behaviour of macroscopic objects—quantum entanglement, quantum teleportation and the quantum Zeno effect. Taking the interplay between gravity and quantum mechanics as an example, I will review a set of speculations on how quantum mechanics can be modified for macroscopic objects, and how these speculations—and their generalizations—might be tested by optomechanics. (invited review)

Micro-optomechanical trampoline resonators

Science.gov (United States)

Pepper, Brian; Kleckner, Dustin; Sonin, Petro; Jeffrey, Evan; Bouwmeester, Dirk

2011-03-01

Recently, micro-optomechanical devices have been proposed for implementation of experiments ranging from non-demolition measurements of phonon number to creation of macroscopic quantum superpositions. All have strenuous requirements on optical finesse, mechanical quality factor, and temperature. We present a set of devices composed of dielectric mirrors on Si 3 N4 trampoline resonators. We describe the fabrication process and present data on finesse and quality factor. The authors gratefully acknowledge support from NSF PHY-0804177 and Marie Curie EXT-CT-2006-042580.

Laser Theory for Optomechanics: Limit Cycles in the Quantum Regime

Directory of Open Access Journals (Sweden)

Niels Lörch

2014-01-01

Full Text Available Optomechanical systems can exhibit self-sustained limit cycles where the quantum state of the mechanical resonator possesses nonclassical characteristics such as a strongly negative Wigner density, as was shown recently in a numerical study by Qian et al. [Phys. Rev. Lett. 109, 253601 (2012]. Here, we derive a Fokker-Planck equation describing mechanical limit cycles in the quantum regime that correctly reproduces the numerically observed nonclassical features. The derivation starts from the standard optomechanical master equation and is based on techniques borrowed from the laser theory due to Haake and Lewenstein. We compare our analytical model with numerical solutions of the master equation based on Monte Carlo simulations and find very good agreement over a wide and so far unexplored regime of system parameters. As one main conclusion, we predict negative Wigner functions to be observable even for surprisingly classical parameters, i.e., outside the single-photon strong-coupling regime, for strong cavity drive and rather large limit-cycle amplitudes. The approach taken here provides a natural starting point for further studies of quantum effects in optomechanics.

Si{sub 3}N{sub 4} optomechanical crystals in the resolved-sideband regime

Energy Technology Data Exchange (ETDEWEB)

Davanço, M., E-mail: mdavanco@nist.gov [Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Department of Applied Physics, California Institute of Technology, Pasadena, California 91125 (United States); Ates, S.; Liu, Y. [Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Maryland NanoCenter, University of Maryland, College Park, Maryland 20742 (United States); Srinivasan, K. [Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2014-01-27

We demonstrate sideband-resolved Si{sub 3}N{sub 4} optomechanical crystals supporting 10{sup 5} quality factor optical modes at 980 nm, coupled to ≈4 GHz frequency mechanical modes with quality factors of ≈3000. Optomechanical electromagnetically induced transparency and absorption are observed at room temperature and in atmosphere with intracavity photon numbers in excess of 10{sup 4}.

Wavelength-modulated spectroscopy of the sub-bandgap response of solar cell devices

Energy Technology Data Exchange (ETDEWEB)

Mandanirina, N.H., E-mail: s213514095@nmmu.ac.za; Botha, J.R.; Wagener, M.C.

2016-01-01

A wavelength-modulation setup for measuring the differential photo-response of a GaSb/GaAs quantum ring solar cell structure is reported. The pseudo-monochromatic wavelength is modulated at the output of a conventional monochromator by means of a vibrating slit mechanism. The vibrating slit was able to modulate the excitation wavelength up to 33 nm. The intensity of the light beam was kept constant through a unique flux correction module, designed and built in-house. The setup enabled measurements in the near-infrared range (from 1000 to 1300 nm), which is specifically used to probe the sub-band gap differential photo-response of GaAs solar cells.

On-chip microparticle detection and sizing using a dual-wavelength waveguide laser

NARCIS (Netherlands)

Bernhardi, Edward H.; van der Werf, Kees O; Hollink, Anton J F; Worhoff, Kerstin; De Ridder, Rene M.; Subramaniam, Vinod; Pollnau, Markus

2013-01-01

An integrated intra-laser-cavity microparticle sensor based on a dual-phase-shift, dual-wavelength distributed-feedback channel waveguide laser in Al2O3:Yb3+ is presented. Real-time detection and accurate size measurement of single microparticles with diameters ranging between 1 μm and 20 μm are

Transient surface states during the CBE growth of GaAs

Science.gov (United States)

Farrell, T.; Hill, D.; Joyce, T. B.; Bullough, T. J.; Weightman, P.

1997-05-01

We report the occurrence of a transient surface state during the initial stages of CBE GaAs(0 0 1) growth. The state was detected in real-time reflectance ( R) and reflectance anisotropy spectroscopy (RAS) growth monitoring. At low growth rates, less than 1 μm/h, beam equivalent pressure (BEP) of triethylgallium (TEG) BEPs there was a rapid increase in R at all monitoring wavelengths, followed by a monotonic decay to its pre-growth value. This transient increase in R was accompanied by a change in the RAS signal, the magnitude and sign of which varied with wavelength. The initial increase in R is shown to be associated with the development of a metallic-like surface whereas the changes in the RAS signal are consistent with the formation of Ga dimers.

The effects of temperature, hydrostatic pressure and size on optical gain for GaAs spherical quantum dot laser with hydrogen impurity

Science.gov (United States)

Owji, Erfan; Keshavarz, Alireza; Mokhtari, Hosein

2016-10-01

In this paper, the effects of temperature, hydrostatic pressure and size on optical gain for GaAs spherical quantum dot laser with hydrogen impurity are investigated. For this purpose, the effects of temperature, pressure and quantum dot size on the band gap energy, effective mass, and dielectric constant are studied. The eigenenergies and eigenstates for valence and conduction band are calculated by using Runge-Kutta numerical method. Results show that changes in the temperature, pressure and size lead to the alteration of the band gap energy and effective mass. Also, increasing the temperature redshifts the optical gain peak and at special temperature ranges lead to increasing or decreasing of it. Further, by reducing the size, temperature-dependent of optical gain is decreased. Additionally, enhancing of the hydrostatic pressure blueshifts the peak of optical gain, and its behavior as a function of pressure which depends on the size. Finally, increasing the radius rises the redshifts of the peak of optical gain.

Nonlinear optomechanical measurement of mechanical motion

DEFF Research Database (Denmark)

Brawley, G.A.; Vanner, M R; Larsen, Peter Emil

2016-01-01

Precision measurement of nonlinear observables is an important goal in all facets of quantum optics. This allows measurement-based non-classical state preparation, which has been applied to great success in various physical systems, and provides a route for quantum information processing with oth......Precision measurement of nonlinear observables is an important goal in all facets of quantum optics. This allows measurement-based non-classical state preparation, which has been applied to great success in various physical systems, and provides a route for quantum information processing...... with otherwise linear interactions. In cavity optomechanics much progress has been made using linear interactions and measurement, but observation of nonlinear mechanical degrees-of-freedom remains outstanding. Here we report the observation of displacement-squared thermal motion of a micro-mechanical resonator...... by exploiting the intrinsic nonlinearity of the radiation-pressure interaction. Using this measurement we generate bimodal mechanical states of motion with separations and feature sizes well below 100 pm. Future improvements to this approach will allow the preparation of quantum superposition states, which can...

X-ray diffraction from single GaAs nanowires

Energy Technology Data Exchange (ETDEWEB)

Biermanns, Andreas

2012-11-12

In recent years, developments in X-ray focussing optics have allowed to produce highly intense, coherent X-ray beams with spot sizes in the range of 100 nm and below. Together with the development of new experimental stations, X-ray diffraction techniques can now be applied to study single nanometer-sized objects. In the present work, X-ray diffraction is applied to study different aspects of the epitaxial growth of GaAs nanowires. Besides conventional diffraction methods, which employ X-ray beams with dimensions of several tens of {mu}m, special emphasis lies on the use of nanodiffraction methods which allow to study single nanowires in their as-grown state without further preparation. In particular, coherent X-ray diffraction is applied to measure simultaneously the 3-dimensional shape and lattice parameters of GaAs nanowires grown by metal-organic vapor phase epitaxy. It is observed that due to a high density of zinc-blende rotational twins within the nanowires, their lattice parameter deviates systematically from the bulk zinc-blende phase. In a second step, the initial stage in the growth of GaAs nanowires on Si (1 1 1) surfaces is studied. This nanowires, obtained by Ga-assisted growth in molecular beam epitaxy, grow predominantly in the cubic zinc-blende structure, but contain inclusions of the hexagonal wurtzite phase close to their bottom interface. Using nanodiffraction methods, the position of the different structural units along the growth axis is determined. Because the GaAs lattice is 4% larger than silicon, these nanowires release their lattice mismatch by the inclusion of dislocations at the interface. Whereas NWs with diameters below 50 nm are free of strain, a rough interface structure in nanowires with diameters above 100 nm prevents a complete plastic relaxation, leading to a residual strain at the interface that decays elastically along the growth direction. Finally, measurements on GaAs-core/InAs-shell nanowire heterostructures are presented

Dynamical back-action effects in low loss optomechanical oscillators

Energy Technology Data Exchange (ETDEWEB)

Pontin, Antonio; Prodi, Giovanni A. [INFN, Trento Institute for Fundamental Physics and Application, Povo (Italy); Dipartimento di Fisica, Universita di Trento, Povo (Italy); Bonaldi, Michele; Borrielli, Antonio [INFN, Trento Institute for Fundamental Physics and Application, Povo (Italy); Institute of Materials for Electronics and Magnetism, Nanoscience-Trento-FBK Division, Povo (Italy); Marino, Francesco [INFN, Sezione di Firenze, Sesto Fiorentino (Italy); CNR-INO, Firenze (Italy); Marconi, Lorenzo [LENS, Sesto Fiorentino (Italy); Bagolini, Alvise [Microtechnology Laboratory FBK-CMM, Povo (Italy); Pandraud, Gregory [DIMES Technology Center-TU Delft (Netherlands); Serra, Enrico [INFN, Trento Institute for Fundamental Physics and Application, Povo (Italy); DIMES Technology Center-TU Delft (Netherlands); Interdisciplinary Laboratory for Computational Science (LISC), FBK-University of Trento, Povo (Italy); Marin, Francesco [INFN, Sezione di Firenze, Sesto Fiorentino (Italy); LENS, Sesto Fiorentino (Italy); Dipartimento di Fisica e Astronomia, Universita di Firenze, Sesto Fiorentino (Italy)

2015-01-01

The problem of the stability of a cavity optomechanical system based on an oscillator having at the same time low optical and mechanical losses is addressed. As it is the aim to extend the use of optical squeezing as a tool for improving quantum limited displacement sensing at low frequency, a family of opto-mechanical devices designed to work at frequencies of about 100 kHz was developed. The devices actually meet the initial design goals, but new requirements have emerged from the analysis of their behavior in optical cavities, due to the interaction between the cavity locking system and the low order normal modes of the devices. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Wavelength tuning of InAs quantum dots grown on InP (100) by chemical-beam epitaxy

International Nuclear Information System (INIS)

Gong, Q.; Noetzel, R.; Veldhoven, P.J. van; Eijkemans, T.J.; Wolter, J.H.

2004-01-01

We report on an effective way to continuously tune the emission wavelength of InAs quantum dots (QDs) grown on InP (100) by chemical-beam epitaxy. The InAs QD layer is embedded in a GaInAsP layer lattice matched to InP. With an ultrathin GaAs layer inserted between the InAs QD layer and the GaInAsP buffer, the peak wavelength from the InAs QDs can be continuously tuned from above 1.6 μm down to 1.5 μm at room temperature. The major role of the thin GaAs layer is to greatly suppress the As/P exchange during the deposition of InAs and subsequent growth interruption under arsenic flux, as well as to consume the segregated surface In layer floating on the GaInAsP buffer layer

Photoabsorption modulation in GaAs: Ga1-xInx as strained-layer superlattices

International Nuclear Information System (INIS)

Sella, I.; Watkins, D.E.; Laurich, B.K.; Smith, D.L.; Subbanna, S.; Kroemer, H.

1990-01-01

Photoabsorption modulation measurements have been made on Ga 1 -x In x As -- GaAs strained-layer superlattices using two approaches: In the first the modulating beam and the test beam have the same wavelength (near the exciton resonance). In the second, the modulation wavelength is much shorter than the test beam wavelength. A dramatic difference is observed in the modulated transmission spectra near the excitonic level for the two modulating wavelengths. The difference in behavior can be explained by screening of the residual surface electric field, which only occurs for the high photon energy modulating beam. This beam excites carriers that are free to drift in the surface field before they are captured in the quantum wells. Carriers excited by the low photon energy modulation beam are created in the wells and can not effectively screen the surface field. We describe a model which explains the nonlinear intensity saturation profile and qualitatively describes the spectral line shape. 4 refs., 4 figs

Mesoscopic chaos mediated by Drude electron-hole plasma in silicon optomechanical oscillators

Science.gov (United States)

Wu, Jiagui; Huang, Shu-Wei; Huang, Yongjun; Zhou, Hao; Yang, Jinghui; Liu, Jia-Ming; Yu, Mingbin; Lo, Guoqiang; Kwong, Dim-Lee; Duan, Shukai; Wei Wong, Chee

2017-01-01

Chaos has revolutionized the field of nonlinear science and stimulated foundational studies from neural networks, extreme event statistics, to physics of electron transport. Recent studies in cavity optomechanics provide a new platform to uncover quintessential architectures of chaos generation and the underlying physics. Here, we report the generation of dynamical chaos in silicon-based monolithic optomechanical oscillators, enabled by the strong and coupled nonlinearities of two-photon absorption induced Drude electron–hole plasma. Deterministic chaotic oscillation is achieved, and statistical and entropic characterization quantifies the chaos complexity at 60 fJ intracavity energies. The correlation dimension D2 is determined at 1.67 for the chaotic attractor, along with a maximal Lyapunov exponent rate of about 2.94 times the fundamental optomechanical oscillation for fast adjacent trajectory divergence. Nonlinear dynamical maps demonstrate the subharmonics, bifurcations and stable regimes, along with distinct transitional routes into chaos. This provides a CMOS-compatible and scalable architecture for understanding complex dynamics on the mesoscopic scale. PMID:28598426

Opto-mechanical assembly procurement for the National Ignition Facility

International Nuclear Information System (INIS)

House, W.; Simon, T.

1999-01-01

A large number of the small optics procurements for the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) will be in the form of completely assembled, tested, and cleaned subsystems. These subsystems will be integrated into the NIF at LLNL. To accomplish this task, the procurement packages will include, optical and mechanical drawings, acceptance test and cleanliness requirements. In January 1999, the first such integrated opto-mechanical assembly was received and evaluated at LLNL. With the successful completion of this important trial procurement, we were able to establish the viability of purchasing clean, ready to install, opto-mechanical assemblies from vendors within the optics industry. 32 vendors were chosen from our supplier database for quote, then five were chosen to purchase from. These five vendors represented a cross section of the optics industry. From a ''value'' catalog supplier (that did the whole job internally) to a partnership between three specialty companies, these vendors demonstrated they have the ingenuity and capability to deliver cost competitive, NIF-ready, opto- mechanical assemblies. This paper describes the vendor selection for this procurement, technical requirements including packaging, fabrication, coating, and cleanliness specifications, then testing and verification. It also gives real test results gathered from inspections performed at LLNL that show how our vendors scored on the various requirements. Keywords: Opto-Mechanical, assembly, NIF, packaging, shipping, specifications, procurement, MIL-STD-1246C, surface cleanliness

Controllable photon and phonon localization in optomechanical Lieb lattices.

Science.gov (United States)

Wan, Liang-Liang; Lü, Xin-You; Gao, Jin-Hua; Wu, Ying

2017-07-24

The Lieb lattice featuring flat band is not only important in strongly-correlated many-body physics, but also can be utilized to inspire new quantum devices. Here we propose an optomechanical Lieb lattice, where the flat-band physics of photon-phonon polaritons is demonstrated. The tunability of the band structure of the optomechanical arrays allows one to obtain an approximate photon or phonon flat band as well as the transition between them. This ultimately leads to the result that the controllable photon or phonon localization could be realized by the path interference effects. This study offers an alternative approach to explore the exotic photon and phonon many-body effects, which has potential applications in the future hybrid-photon-phonon quantum network and engineering new type solid-state quantum devices.

Cooperative effects between color centers in diamond: applications to optical tweezers and optomechanics

Science.gov (United States)

Bradac, Carlo; Prasanna Venkatesh, B.; Besga, Benjamin; Johnsson, Mattias; Brennen, Gavin; Molina-Terriza, Gabriel; Volz, Thomas; Juan, Mathieu L.

2017-08-01

Since the early work by Ashkin in 1970,1 optical trapping has become one of the most powerful tools for manipulating small particles, such as micron sized beads2 or single atoms.3 Interestingly, both an atom and a lump of dielectric material can be manipulated through the same mechanism: the interaction energy of a dipole and the electric field of the laser light. In the case of atom trapping, the dominant contribution typically comes from the allowed optical transition closest to the laser wavelength while it is given by the bulk polarisability for mesoscopic particles. This difference lead to two very different contexts of applications: one being the trapping of small objects mainly in biological settings,4 the other one being dipole traps for individual neutral atoms5 in the field of quantum optics. In this context, solid state artificial atoms present the interesting opportunity to combine these two aspects of optical manipulation. We are particularly interested in nanodiamonds as they constitute a bulk dielectric object by themselves, but also contain artificial atoms such as nitrogen-vacancy (NV) or silicon-vacancy (SiV) colour centers. With this system, both regimes of optical trapping can be observed at the same time even at room temperature. In this work, we demonstrate that the resonant force from the optical transition of NV centres at 637 nm can be measured in a nanodiamond trapped in water. This additional contribution to the total force is significant, reaching up to 10%. In addition, due to the very large density of NV centres in a sub-wavelength crystal, collective effects between centres have an important effect on the magnitude of the resonant force.6 The possibility to observe such cooperatively enhanced optical force at room temperature is also theoretically confirmed.7 This approach may enable the study of cooperativity in various nanoscale solid-state systems and the use of atomic physics techniques in the field of nano-manipulation and opto-mechanics.

PHASES: Opto-mechanical solutions to perform absolute spectrophotometry from space

Directory of Open Access Journals (Sweden)

Vather Dinesh

2013-04-01

Full Text Available This work provides an update of the current status of PHASES, which is a project aimed at developing a space-borne telescope to perform absolute flux calibrated spectroscopy of bright stars. PHASES will make it possible to measure micromagnitude photometric variations due to, e.g., exo-planet/moon transits. It is designed to obtain 1% RMS flux calibrated low resolution spectra in the wavelength range 370–960 nm with signal-to-noise ratios >100 for stars with V<10 in short integration times of ∼1 minute. The strategy to calibrate the system using A-type stars is outlined. PHASES will make possible a complete characterization of stars, some of them hosting planets. From the comparison of observed spectra with accurate model atmospheres stellar angular diameters will be determined with precisions of ∼0.5%. The light curves of transiting systems will be then used to extract the radius of the planet with similar precision. The demanding scientific requirements to be achieved under extreme observing conditions have shaped the optomechanical design. A computational model and a high-precision interferometric system have been developed to test the performance of the instrument.

Lithium compensation of GaAs

International Nuclear Information System (INIS)

Alexiev, D.; Tavendale, A.J.

1988-08-01

Defects generated following Li diffusion into GaAs were studied by optical deep level transient spectroscopy (ODLTS) and deep level transient spectroscopy (DLTS). In an exploratory series of experiments, the effect of Li diffusion on existing trap spectra, defect generation and as a means for the compensation of GaAs was studied. The variables included diffusion temperature, initial trap spectra of GaAs and annealing periods. Detailed measurements of trap energies were made

A low-frequency chip-scale optomechanical oscillator with 58 kHz mechanical stiffening and more than 100th-order stable harmonics.

Science.gov (United States)

Huang, Yongjun; Flores, Jaime Gonzalo Flor; Cai, Ziqiang; Yu, Mingbin; Kwong, Dim-Lee; Wen, Guangjun; Churchill, Layne; Wong, Chee Wei

2017-06-29

For the sensitive high-resolution force- and field-sensing applications, the large-mass microelectromechanical system (MEMS) and optomechanical cavity have been proposed to realize the sub-aN/Hz 1/2 resolution levels. In view of the optomechanical cavity-based force- and field-sensors, the optomechanical coupling is the key parameter for achieving high sensitivity and resolution. Here we demonstrate a chip-scale optomechanical cavity with large mass which operates at ≈77.7 kHz fundamental mode and intrinsically exhibiting large optomechanical coupling of 44 GHz/nm or more, for both optical resonance modes. The mechanical stiffening range of ≈58 kHz and a more than 100 th -order harmonics are obtained, with which the free-running frequency instability is lower than 10 -6 at 100 ms integration time. Such results can be applied to further improve the sensing performance of the optomechanical inspired chip-scale sensors.

Mechanical Resonators for Quantum Optomechanics Experiments at Room Temperature.

Science.gov (United States)

Norte, R A; Moura, J P; Gröblacher, S

2016-04-08

All quantum optomechanics experiments to date operate at cryogenic temperatures, imposing severe technical challenges and fundamental constraints. Here, we present a novel design of on-chip mechanical resonators which exhibit fundamental modes with frequencies f and mechanical quality factors Q_{m} sufficient to enter the optomechanical quantum regime at room temperature. We overcome previous limitations by designing ultrathin, high-stress silicon nitride (Si_{3}N_{4}) membranes, with tensile stress in the resonators' clamps close to the ultimate yield strength of the material. By patterning a photonic crystal on the SiN membranes, we observe reflectivities greater than 99%. These on-chip resonators have remarkably low mechanical dissipation, with Q_{m}∼10^{8}, while at the same time exhibiting large reflectivities. This makes them a unique platform for experiments towards the observation of massive quantum behavior at room temperature.

Optical-response properties in hybrid optomechanical systems with quadratic coupling

Science.gov (United States)

Sun, Xue-Jian; Wang, Xin; Liu, Li-Na; Liu, Wen-Xiao; Fang, Ai-Ping; Li, Hong-Rong

2018-02-01

We theoretically investigate the optical-response properties of the four-mode quadratically coupled optomechanical system (OMS), in which two standard OMSs with quadratic coupling are coupled to each other via a common waveguide. In the presence of a strong control field applied to one cavity and a weak probe field applied to the other, we show that by suitably tuning the system parameters, there appears the normal mode splitting, optomechanically induced absorption, and double or triple electromagnetically induced transparency phenomena in the probe absorption spectrum. In particular, the explicit physical explanations for those fantastic phenomena are detailed discussed. Moreover, we also show that our proposal can be exploited to implement the optical switch as well as the slow and fast light effects.

Electron spin control and torsional optomechanics of an optically levitated nanodiamond in vacuum

Science.gov (United States)

Li, Tongcang; Hoang, Thai; Ahn, Jonghoon; Bang, Jaehoon

Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centers, indicating potential applications of NV centers in oxygen gas sensing. For spin-optomechanics, it is important to control the orientation of the nanodiamond and NV centers in a magnetic field. Recently, we have observed the angular trapping and torsional vibration of a levitated nanodiamond, which paves the way towards levitated torsional optomechanics in the quantum regime. NSF 1555035-PHY.

Multiple electromechanically-induced-transparency windows and Fano resonances in hybrid nano-electro-optomechanics

Science.gov (United States)

Ullah, Kamran; Jing, Hui; Saif, Farhan

2018-03-01

We show multiple electromechanically-induced transparency (EMIT) windows in a hybrid nano-electro-optomechanical system in the presence of two-level atoms coupled to a single-mode cavity field. The multiple EMIT-window profile can be observed by controlling the atom field coupling as well as Coulomb coupling between the two charged mechanical resonators. We derive the analytical expression of the multiple-EMIT-windows profile and describe the splitting of multiple EMIT windows as a function of optomechanical coupling, atom-field coupling, and Coulomb coupling. In particular, we discuss the robustness of the system against the cavity decay rate. We compare the results of identical mechanical resonators to different mechanical resonators. We further show how the hybrid nano-electro-optomechanics coupled system can lead to the splitting of the multiple Fano resonances (MFR). The Fano resonances are very sensitive to decay terms in such systems, i.e., atoms, cavities, and the mechanical resonators.

Enhanced optomechanical readout using optical coalescence

DEFF Research Database (Denmark)

Genes, Claudiu; Xuereb, André; Pupillo, Guido

2013-01-01

of a symmetric Fabry-Pérot resonator strongly modifies the cavity response function, such that two longitudinal modes with different spatial parity are brought close to frequency degeneracy and interfere in the cavity output field. In the case of a movable middle reflector we show that the interference...... in this generic “optical coalescence” phenomenon gives rise to an enhanced frequency shift of the peaks of the cavity transmission that can be exploited in optomechanics....

Performance, size, mass, and cost estimates for projected 1kW EOL Si, InP, and GaAs arrays

Science.gov (United States)

Slifer, Luther W., Jr.

1991-01-01

One method of evaluating the potential of emerging solar cell and array technologies is to compare their projected capabilities in space flight applications to those of established Si solar cells and arrays. Such an application-oriented comparison provides an integrated view of the elemental comparisons of efficiency, radiation resistance, temperature sensitivity, size, mass, and cost in combination. In addition, the assumptions necessary to make the comparisons provide insights helpful toward determining necessary areas of development or evaluation. Finally, as developments and evaluations progress, the results can be used in more precisely defining the overall potential of the new technologies in comparison to existing technologies. The projected capabilities of Si, InP, and GaAs cells and arrays are compared.

Enhancing quantum effects via periodic modulations in optomechanical systems

Science.gov (United States)

Farace, Alessandro; Giovannetti, Vittorio

2012-07-01

Parametrically modulated optomechanical systems have been recently proposed as a simple and efficient setting for the quantum control of a micromechanical oscillator: relevant possibilities include the generation of squeezing in the oscillator position (or momentum) and the enhancement of entanglement between mechanical and radiation modes. In this paper we further investigate this modulation regime, considering an optomechanical system with one or more parameters being modulated over time. We first apply a sinusoidal modulation of the mechanical frequency and characterize the optimal regime in which the visibility of purely quantum effects is maximal. We then introduce a second modulation on the input laser intensity and analyze the interplay between the two. We find that an interference pattern shows up, so that different choices of the relative phase between the two modulations can either enhance or cancel the desired quantum effects, opening new possibilities for optimal quantum control strategies.

Directional amplifier in an optomechanical system with optical gain

Science.gov (United States)

Jiang, Cheng; Song, L. N.; Li, Yong

2018-05-01

Directional amplifiers are crucial nonreciprocal devices in both classical and quantum information processing. Here we propose a scheme for realizing a directional amplifier between optical and microwave fields based on an optomechanical system with optical gain, where an active optical cavity and two passive microwave cavities are coupled to a common mechanical resonator via radiation pressure. The two passive cavities are coupled via hopping interaction to facilitate the directional amplification between the active and passive cavities. We obtain the condition of achieving optical directional amplification and find that the direction of amplification can be controlled by the phase differences between the effective optomechanical couplings. The effects of the gain rate of the active cavity and the effective coupling strengths on the maximum gain of the amplifier are discussed. We show that the noise added to this amplifier can be greatly suppressed in the large cooperativity limit.

Schottky barrier measurements on individual GaAs nanowires by X-ray photoemission microscopy

Energy Technology Data Exchange (ETDEWEB)

Di Mario, Lorenzo [IMM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy); Turchini, Stefano, E-mail: stefano.turchini@cnr.it [ISM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy); Zamborlini, Giovanni; Feyer, Vitaly [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, 52425 Jülich (Germany); Tian, Lin [IMM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy); Schneider, Claus M. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, 52425 Jülich (Germany); Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, D-47048 Duisburg (Germany); Rubini, Silvia [IOM-CNR, TASC Laboratory, Basovizza 34149, Trieste (Italy); Martelli, Faustino, E-mail: faustino.martelli@cnr.it [IMM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy)

2016-11-15

Highlights: • The Schottky barrier at the interface between Cu and GaAs nanowires was measured. • Individual nanowires were investigated by X-ray Photoemission Microscopy. • The Schottky barrier at different positions along the nanowire was evaluated. - Abstract: We present measurements of the Schottky barrier height on individual GaAs nanowires by means of x-ray photoelectron emission microscopy (XPEEM). Values of 0.73 and 0.51 eV, averaged over the entire wires, were measured on Cu-covered n-doped and p-doped GaAs nanowires, respectively, in agreement with results obtained on bulk material. Our measurements show that XPEEM can become a feasible and reliable investigation tool of interface formation at the nanoscale and pave the way towards the study of size-dependent effects on semiconductor-based structures.

Design optimization of GaAs betavoltaic batteries

International Nuclear Information System (INIS)

Chen Haiyanag; Jiang Lan; Chen Xuyuan

2011-01-01

GaAs junctions are designed and fabricated for betavoltaic batteries. The design is optimized according to the characteristics of GaAs interface states and the diffusion length in the depletion region of GaAs carriers. Under an illumination of 10 mCi cm -2 63 Ni, the open circuit voltage of the optimized batteries is about ∼0.3 V. It is found that the GaAs interface states induce depletion layers on P-type GaAs surfaces. The depletion layer along the P + PN + junction edge isolates the perimeter surface from the bulk junction, which tends to significantly reduce the battery dark current and leads to a high open circuit voltage. The short circuit current density of the optimized junction is about 28 nA cm -2 , which indicates a carrier diffusion length of less than 1 μm. The overall results show that multi-layer P + PN + junctions are the preferred structures for GaAs betavoltaic battery design.

Longer than 1.9 μm photoluminescence emission from InAs quantum structure on GaAs (001) substrate

Energy Technology Data Exchange (ETDEWEB)

Liu, Ke; Ma, Wenquan, E-mail: wqma@semi.ac.cn; Huang, Jianliang; Zhang, Yanhua; Cao, Yulian; Huang, Wenjun; Luo, Shuai; Yang, Tao [Institute of Semiconductors, Chinese Academy of Sciences, Qinghua East Road A 35, Beijing 100083 (China)

2015-07-27

We report on photoluminescence (PL) emission with long wavelength for quantum structure by the sub-monolayer (SML) growth technique on GaAs (001) substrate. It is found that the PL emission wavelength can be controlled by controlling the SML InAs deposition amount. At 12 K, the PL peak position of the grown samples changes from about 1.66 to 1.78 μm. At 120 K, the PL emission of a sample reaches 1.91 μm. The physical mechanism responsible for the measured long wavelength PL emission may be related to strong In segregation and intermixing effects occurred in the structure grown by SML growth technique.

Hot electron emission can lead to damping of optomechanical modes in core-shell Ag@TiO₂ nanocubes

DEFF Research Database (Denmark)

Tamulevičius, Sigitas; Peckus, Domantas; Rong, Hongpan

2017-01-01

Interactions between light and metal nanostructures are mediated by collective excitations of free electrons called surface plasmons, which depend primarily on geometry and dielectric environment. Excitation with ultrafast pulses can excite optomechanical modes that modulate the volume and shape...... resonance is being lost to the TiO2 as hot carriers instead of coupling to the optomechanical mode. Analysis of both ultrafast decay and characterization of optomechanical modes provides a dual accounting method to track energy dissipation in hybrid metal-semiconductor nanosystems for plasmon-enhanced solar...

Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

Science.gov (United States)

Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

2012-06-01

GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

Parameters study on the growth of GaAs nanowires on indium tin oxide by metal-organic chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Wu, Dan; Tang, Xiaohong, E-mail: exhtang@ntu.edu.sg, E-mail: wangk@sustc.edu.cn; Li, Xianqiang [OPTIMUS, Photonics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore (Singapore); Wang, Kai, E-mail: exhtang@ntu.edu.sg, E-mail: wangk@sustc.edu.cn [Department of Electrical & Electronic Engineering, South University of Science and Technology of China, 1088 Xueyuan Avenue, Shenzhen 518055 (China); Olivier, Aurelien [CINTRA UMI 3288, School of Electrical and Electronic Engineering, Nanyang Technological University, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, 637553 Singapore (Singapore)

2016-03-07

After successful demonstration of GaAs nanowire (NW) epitaxial growth on indium tin oxide (ITO) by metal organic chemical vapor deposition, we systematically investigate the effect of growth parameters' effect on the GaAs NW, including temperature, precursor molar flow rates, growth time, and Au catalyst size. 40 nm induced GaAs NWs are observed with zinc-blende structure. Based on vapor-liquid-solid mechanism, a kinetic model is used to deepen our understanding of the incorporation of growth species and the role of various growth parameters in tuning the GaAs NW growth rate. Thermally activated behavior has been investigated by variation of growth temperature. Activation energies of 40 nm Au catalyst induced NWs are calculated at different trimethylgallium (TMGa) molar flow rates about 65 kJ/mol. The GaAs NWs growth rates increase with TMGa molar flow rates whereas the growth rates are almost independent of growth time. Due to Gibbs-Thomson effect, the GaAs NW growth rates increase with Au nanoparticle size at different temperatures. Critical radius is calculated as 2.14 nm at the growth condition of 430 °C and 1.36 μmol/s TMGa flow rate. It is also proved experimentally that Au nanoparticle below the critical radius such as 2 nm cannot initiate the growth of NWs on ITO. This theoretical and experimental growth parameters investigation enables great controllability over GaAs NWs grown on transparent conductive substrate where the methodology can be expanded to other III–V material NWs and is critical for potential hybrid solar cell application.

Dynamical back-action at 5.5 GHz in a corrugated optomechanical beam

Energy Technology Data Exchange (ETDEWEB)

Navarro-Urrios, D., E-mail: daniel.navarrourrios@nano.cnr.it [Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, Edifici ICN2, 08193 Bellaterra (Spain); NEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, I-56127 (Italy); Gomis-Bresco, J.; Alzina, F. [Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, Edifici ICN2, 08193 Bellaterra (Spain); El-Jallal, S. [IEMN, Universite de Lille 1, Villeneuve d’Ascq (France); PRILM, Université Moulay Ismail, Faculté des sciences, Meknès (Morocco); Oudich, M.; Pennec, Y.; Djafari-Rouhani, B. [IEMN, Universite de Lille 1, Villeneuve d’Ascq (France); Pitanti, A. [NEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, I-56127 (Italy); Capuj, N. [Depto. Física, Universidad de la Laguna, 38206 (Spain); Tredicucci, A. [NEST, Istituto Nanoscienze – CNR and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, I-56127 (Italy); Dipartimento di Fisica, Universita di Pisa, Largo Pontecorvo 3, I-56127 Pisa (Italy); Griol, A.; Martínez, A. [Nanophotonics Technology Center, Universitat Politècnica de València, Valencia (Spain); Sotomayor Torres, C. M. [Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, Edifici ICN2, 08193 Bellaterra (Spain); Catalan Institution for Research and Advanced Studies (ICREA), 08010 Barcelona (Spain)

2014-12-15

We report on the optomechanical properties of a breathing mechanical mode oscillating at 5.5 GHz in a 1D corrugated Si nanobeam. This mode has an experimental single-particle optomechanical coupling rate of |g{sub o,OM}| = 1.8 MHz (|g{sub o,OM}|/2π = 0.3 MHz) and shows strong dynamical back-action effects at room temperature. The geometrical flexibility of the unit-cell would lend itself to further engineering of the cavity region to localize the mode within the full phononic band-gap present at 4 GHz while keeping high g{sub o,OM} values. This would lead to longer lifetimes at cryogenic temperatures, due to the suppression of acoustic leakage.

Coherent interference effects and squeezed light generation in optomechanical systems

Science.gov (United States)

Qu, Kenan

My Ph.D. dissertation is on the fundamental effects in optomechanical systems (OMS) and their important applications. The OMS are based on the possibility of the mechanical motion produced by few photons incident on the mechanical device. This dissertation presents several applications of the OMS in the area of storage of light in long-lived phonons, single mode optomechanical Ramsey interferometry, and generation of large amount of squeezing in the output radiation. The long-lived phonons can be monitored and controlled via optical means as was experimentally demonstrated. To show this, I develop the theory of transient electromagnetically induced transparency (EIT). For further applications like state transfer, especially over very different frequency regimes, I consider double-cavity OMS, where the two cavities can correspond to different spectral domains, yet the state transfer is possible via phonons. The state transfer is based on a new effect, electromagnetically induced absorption (EIA), where one uses a second control field from the other cavity to produce an absorption peak inside the EIT window. All these involve the interference of various path ways via which a final state is reached. The following chapter shows how Fano-like interference can arise in OMS. A Fano asymmetry parameter for OMS was defined. The last two chapters deal with the question if OMS can be efficient generators of squeezed light. I show by blue and red tuning the two cavities in a double-cavity OMS, one can generate effectively a two-mode parametric interaction which yields two-mode squeezed output with the squeezing magnitude of the order of 10dB. This requires a bath temperature of 10mK. Such temperatures obtained by using Helium dilution refrigerator are routinely used with superconducting OMS. The major part of this dissertation is devoted to the dispersive optomechanical interaction. However, the interaction can also be dissipative, where the mechanical displacement modulates

Growth-temperature- and thermal-anneal-induced crystalline reorientation of aluminum on GaAs (100) grown by molecular beam epitaxy

International Nuclear Information System (INIS)

Liu, H. F.; Chua, S. J.; Xiang, N.

2007-01-01

The authors investigated the growth of Al thin films on GaAs (100) substrates by molecular beam epitaxy. It is found that the growth at 550 degree sign C results in a texture that consists of (100)Al[010](parallel sign)(100)GaAs[011] and (100)Al[010](parallel sign)(100)GaAs[010] rotated 45 degree sign with respect to each other, while the growth at 300 degree sign C leads to a mixture phase of (100)Al[010](parallel sign)(100)GaAs[011] and (110)Al[001](parallel sign)(100)GaAs[011]. In situ annealing of the Al film grown at 300 degree sign C causes a reorientation of the crystalline from (100)Al[010](parallel sign)(100)GaAs[011] to (110)Al[001](parallel sign)(100)GaAs[011]. The grain sizes of the Al film are increased by the increased growth temperature and in situ annealing; the ratio of the exposed to the covered surface is not changed significantly by changing the growth temperature but decreased by annealing; and the small islands in between the large ones are removed by annealing. These observations are explained based on island migration and coalescence

Macroscopic Entangled State Generation with Optomechanical Coupling of Two Mechanical Modes

Science.gov (United States)

Weaver, Matthew; Luna, Fernando; Buters, Frank; Heeck, Kier; de Man, Sven; Bouwmeester, Dirk

Mechanical resonators with a large quantum position uncertainty are an excellent test system for proposed decoherence mechanisms in massive systems. We present a scheme to optomechanically entangle two mechanical resonators with large frequency separation via two tone driving and single photon projection measurements. The quantum position uncertainty can be tuned with a variable optical pulse displacement operation, and independent single photon readout of the two resonators provides robust verification of the quantum states of the system. This scheme is currently experimentally feasible in a number of high mass opto- and electro-mechanical systems. We demonstrate one such system with two spatially and frequency separated Si3N4 trampoline resonators. We also show how the resonators can be coupled with two tone driving and the single photon optomechanical coupling rates can be tuned.

Peeled film GaAs solar cell development

International Nuclear Information System (INIS)

Wilt, D.M.; Thomas, R.D.; Bailey, S.G.; Brinker, D.J.; DeAngelo, F.L.

1990-01-01

Thin film, single crystal gallium arsenide (GaAs) solar cells could exhibit a specific power approaching 700 W/Kg including coverglass. A simple process has been described whereby epitaxial GaAs layers are peeled from a reusable substrate. This process takes advantage of the extreme selectivity (>10 6 ) of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofloric acid (HF). The intent of this work is to demonstrate the feasibility of using the peeled film technique to fabricate high efficiency, low mass GaAs solar cells. We have successfully produced a peeled film GaAs solar cell. The device, although fractured and missing the aluminum gallium arsenide (Al x Ga 1 - x As) window and antireflective (AR) coating, had a Voc of 874 mV and a fill factor of 68% under AMO illumination

Individual GaAs nanorods imaged by coherent X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Pietsch, Ullrich; Biermanns, Andreas; Davydok, Anton [Universitaet Siegen (Germany); Paetzelt, Hendrik [Universitaet Leipzig (Germany); IOM Leipzig (Germany); Diaz, Ana; Metzger, Hartmut [ID01 Beamline, ESRF (France); Gottschalch, Volker [Universitaet Leipzig (Germany)

2010-07-01

Semiconductor nanorods are of particular interest for new semiconductor devices because the nanorod approach can be used to form heterostructures of materials with a large lattice mismatch and to define nanorod arrays with tailored inter-rod distance. However, all applications require objects with uniform physical properties based on uniform morphology. Complementary to electron microscopy techniques, destruction free X-ray diffraction techniques can be used to determine structural and morphological details. Using scanning X-ray diffraction microscopy with a spot size of 220 x 600 nm{sup 2} we were able to inspect individual GaAs nanorods grown by seed-free MOVPE through circular openings in a SiN{sub x} mask in a periodic array with 3 {mu}m spacing on GaAs[111]B. The focussed X-ray beam allows the determination of the strain state of individual rods and in combination with coherent diffraction imaging, we were able to characterize also morphological details. Rods grown at different positions in the array show significant differences in shape, size and strain state.

Cavity Opto-Mechanics using an Optically Levitated Nanosphere

Science.gov (United States)

2010-01-19

center-of-mass motion of a levitated nanosphere. entanglement ∣ optical levitation ∣ quantum information One of the most intriguing questions associated...developed. Outlook An optically levitated opto-mechanical system can have remark- ably long coherence times, which potentially enables quantum phenomena...47) or facilitate novel quantum hybrid architectures (6). Note added: We have become aware of a recent, similar proposal to optically levitate and

Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

Energy Technology Data Exchange (ETDEWEB)

Hendra, P. I. B., E-mail: ib.hendra@gmail.com; Rahayu, F., E-mail: ib.hendra@gmail.com; Darma, Y., E-mail: ib.hendra@gmail.com [Physical Vapor Deposition Laboratory, Physics of Material Electronics Research, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132 (Indonesia)

2014-03-24

Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

Spin dynamics in GaAs and (110)-GaAs heterostructures; Spindynamik in GaAs und (110)-GaAs-Heterostrukturen

Energy Technology Data Exchange (ETDEWEB)

Oertel, Stefan

2012-07-01

This thesis investigates the spin dynamics in both bulk GaAs and (llO)GaAs heterostructures using time- and polarization-resolved photoluminescence spectroscopy. In bulk GaAs the spin relaxation t ime is measured for the first time in the high temperature regime from 280 K to 400 K and is compared to numerical calculations. The numerical calculations are based on the spin relaxation theory of the Dyakonov-Perel mechanism effected by momentum scattering with polar optical phonons and electron-electron scattering and are in good agreement with the experimental results. Measurements of the dependence on the electron density serve to determine the energy dependent proportional factor between the electron density and the effective electron-electron scattering time. Also in bulk GaAs the interaction between the electron spin system and the nuclear spin system is investigated. The measured electron Lande g-factor under the influence of the nuclear magnetic field is used as an indicator to monitor the temporal evolution of the nuclear magnetic field under sustained dynamic nuclear polarization. Measurements with polarization modulated excitation enable the determination of the relevant time scale at which dynamic nuclear polarization takes place. Furthermore, the temporal evolution of the measured electron Lande g-factor shows the complex interplay of the dynamic nuclear polarization, the nuclear spin diffusion and the nuclear spin relaxation. In symmetric (110)-GaAs quantum wells the dependence of the inplane anisotropy of the electron Lande g-factor on the quantum well thickness is determined experimentally. The measurements are in very good agreement with calculations based upon k . p-theory and reveal a maximum of the anisotropy at maximum carrier localization in the quantum well. The origin of the anisotropy that is not present in symmetric (001) quantum wells is qualitatively described by means of a simplified model based on fourth-order perturbation theory. A

Effect of the V{sub As}V{sub Ga} complex defect doping on properties of the semi-insulating GaAs

Energy Technology Data Exchange (ETDEWEB)

Ma, Deming, E-mail: xautmdm@163.com; Qiao, Hongbo; Shi, Wei; Li, Enling [Department of Applied Physics, Xi' an University of Technology, Xi' an 710054 (China)

2014-04-21

The different position V{sub As}V{sub Ga} cluster defect doping in semi-insulating (SI) GaAs has been studied by first-principles calculation based on hybrid density functional theory. Our calculated results show that EL6 level is formed due to the V{sub As}V{sub Ga} complex defect, which is very close to the experimental result. It provides the explanation of the absorption of laser with the wavelength beyond in semi-insulating GaAs. The formation energy of V{sub As}V{sub Ga} complex defect is found to decrease from surface to interior gradually. The conduction band minima and valence band maxima of GaAs (001) surface with the V{sub As}V{sub Ga} complex defect are all located at Γ point, and some defect levels are produced in the forbidden band. In contrast, the conduction band minima and valence band maxima of GaAs with the interior V{sub As}V{sub Ga} complex defect are not located at the same k-point, so it might involve the change of momentum in the electron transition process. The research will help strengthen the understanding of photoelectronic properties and effectively guide the preparation of the SI-GaAs materials.

Development of opto-mechanical tools and procedures for the new generation of RICH-detectors at CERN

CERN Document Server

Laub, M; Ullaland, O

2001-01-01

This thesis is focused on development of opto-mechanical tools and procedures, which would contribute to the achievement of the best possible performance of new Ring Imaging Cherenkov (RICH) detectors. On the base of requirements, given by the physics objective of the LHCb detector, and an analysis of the detector opto-mechanical system, specifications of individual opto-mechanical components were determined. Spherical mirrors, planar mirrors and mirror adjustable mounts were the components of interest. Next, their parameters to be characterised were defined. Possible measurement methods were studied and relevant set ups based on suitable methods were developed. Meanwhile, available modern metrology technologies, like laser operated instruments or digital image processing, were applied with an attempt to innovate them and to increase their achievable performance limits. When applicable, the set ups were automated in order to make the measurements fast and reliable. An optical laboratory, devoted to the charac...

Multi-dimensional single-spin nano-optomechanics with a levitated nanodiamond

Science.gov (United States)

Neukirch, Levi P.; von Haartman, Eva; Rosenholm, Jessica M.; Nick Vamivakas, A.

2015-10-01

Considerable advances made in the development of nanomechanical and nano-optomechanical devices have enabled the observation of quantum effects, improved sensitivity to minute forces, and provided avenues to probe fundamental physics at the nanoscale. Concurrently, solid-state quantum emitters with optically accessible spin degrees of freedom have been pursued in applications ranging from quantum information science to nanoscale sensing. Here, we demonstrate a hybrid nano-optomechanical system composed of a nanodiamond (containing a single nitrogen-vacancy centre) that is levitated in an optical dipole trap. The mechanical state of the diamond is controlled by modulation of the optical trapping potential. We demonstrate the ability to imprint the multi-dimensional mechanical motion of the cavity-free mechanical oscillator into the nitrogen-vacancy centre fluorescence and manipulate the mechanical system's intrinsic spin. This result represents the first step towards a hybrid quantum system based on levitating nanoparticles that simultaneously engages optical, phononic and spin degrees of freedom.

Nitridation of porous GaAs by an ECR ammonia plasma

International Nuclear Information System (INIS)

Naddaf, M; Hullavarad, S S; Ganesan, V; Bhoraskar, S V

2006-01-01

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 deg. C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 deg. C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy

Nitridation of porous GaAs by an ECR ammonia plasma

Energy Technology Data Exchange (ETDEWEB)

Naddaf, M [Center for Advanced Studies in Material Science and Solid State Physics, University of Pune, Pune 411 007 (India); Department of Physics, Atomic Energy Commission of Syria, PO Box 6091, Damascus (Syrian Arab Republic); Hullavarad, S S [Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD 20742 (United States); Ganesan, V [Inter University Consortium, Indore (India); Bhoraskar, S V [Center for Advanced Studies in Material Science and Solid State Physics, University of Pune, Pune 411 007 (India)

2006-02-15

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 deg. C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 deg. C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

Nitridation of porous GaAs by an ECR ammonia plasma

Science.gov (United States)

Naddaf, M.; Hullavarad, S. S.; Ganesan, V.; Bhoraskar, S. V.

2006-02-01

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 °C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 °C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

Scaling of laser-plasma interactions with laser wavelength and plasma size

International Nuclear Information System (INIS)

Max, C.E.; Campbell, E.M.; Mead, W.C.; Kruer, W.L.; Phillion, D.W.; Turner, R.E.; Lasinski, B.F.; Estabrook, K.G.

1983-01-01

Plasma size is an important parameter in wavelength-scaling experiments because it determines both the threshold and potential gain for a variety of laser-plasma instabilities. Most experiments to date have of necessity produced relatively small plasmas, due to laser energy and pulse-length limitations. We have discussed in detail three recent Livermore experiments which had large enough plasmas that some instability thresholds were exceeded or approached. Our evidence for Raman scatter, filamentation, and the two-plasmon decay instability needs to be confirmed in experiments which measure several instability signatures simultaneously, and which produce more quantitative information about the local density and temperature profiles than we have today

Scaling of laser-plasma interactions with laser wavelength and plasma size

Energy Technology Data Exchange (ETDEWEB)

Max, C.E.; Campbell, E.M.; Mead, W.C.; Kruer, W.L.; Phillion, D.W.; Turner, R.E.; Lasinski, B.F.; Estabrook, K.G.

1983-01-25

Plasma size is an important parameter in wavelength-scaling experiments because it determines both the threshold and potential gain for a variety of laser-plasma instabilities. Most experiments to date have of necessity produced relatively small plasmas, due to laser energy and pulse-length limitations. We have discussed in detail three recent Livermore experiments which had large enough plasmas that some instability thresholds were exceeded or approached. Our evidence for Raman scatter, filamentation, and the two-plasmon decay instability needs to be confirmed in experiments which measure several instability signatures simultaneously, and which produce more quantitative information about the local density and temperature profiles than we have today.

Photon–phonon parametric oscillation induced by quadratic coupling in an optomechanical resonator

International Nuclear Information System (INIS)

Zhang, Lin; Ji, Fengzhou; Zhang, Xu; Zhang, Weiping

2017-01-01

A direct photon–phonon parametric effect of quadratic coupling on the mean-field dynamics of an optomechanical resonator in the large-scale-movement regime is found and investigated. Under a weak pumping power, the mechanical resonator damps to a steady state with a nonlinear static response sensitively modified by the quadratic coupling. When the driving power increases beyond the static energy balance, the steady states lose their stabilities via Hopf bifurcations, and the resonator produces stable self-sustained oscillation (limit-circle behavior) of discrete energies with step-like amplitudes due to the parametric effect of quadratic coupling, which can be understood roughly by the power balance between gain and loss on the resonator. A further increase in the pumping power can induce a chaotic dynamic of the resonator via a typical routine of period-doubling bifurcation, but which can be stabilized by the parametric effect through an inversion-bifurcation process back to the limit-circle states. The bifurcation-to-inverse-bifurcation transitions are numerically verified by the maximal Lyapunov exponents of the dynamics, which indicate an efficient way of suppressing the chaotic behavior of the optomechanical resonator by quadratic coupling. Furthermore, the parametric effect of quadratic coupling on the dynamic transitions of an optomechanical resonator can be conveniently detected or traced by the output power spectrum of the cavity field. (paper)

Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

Energy Technology Data Exchange (ETDEWEB)

Kalygina, V. M., E-mail: Kalygina@ngs.ru; Vishnikina, V. V.; Petrova, Yu. S.; Prudaev, I. A.; Yaskevich, T. M. [National Research Tomsk State University (Russian Federation)

2015-03-15

We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga{sub 2}O{sub 3}-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga{sub 2}O{sub 3} crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga{sub 2}O{sub 3} crystallites and become transparent. Under illumination of the Ga{sub 2}O{sub 3}-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga{sub 2}O{sub 3} film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga{sub 2}O{sub 3}-GaAs interface and in the Ga{sub 2}O{sub 3} film.

Intermediate band solar cell simulation use InAs quantum dot in GaAs

International Nuclear Information System (INIS)

Hendra P, I. B.; Rahayu, F.; Sahdan, M. F.; Darma, Y.

2015-01-01

Intermediate band solar cell (IBSC) has become a new approach in increasing solar cell efficiency significantly. One way to create intermediate band is by proposing quantum dots (QD) technology. One of the important aspects in utilizing IBSC is the absorption of light. In this work we simulated the influence of QD arrangement in order to increase absorption coefficient and solar cell efficiency. We also simulated the influence of QD size to capture a wider light spectrum. We present a simple calculation method with low computing power demand. Results show that the increasing in quantum dot size can increase in capturing wider spectrum of light. Arrangement InAs QD in bulk material GaAs can capture wider spectrum of light and increase the absorption coefficient. The arrangement InAs QD 2 nm in GaAs bulk can increase solar cell efficiency up to 49.68%

Impact of GaAs buffer thickness on electronic quality of GaAs grown on graded Ge/GeSi/Si substrates

International Nuclear Information System (INIS)

Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.; Keyes, B. M.

2000-01-01

Minority carrier lifetimes and interface recombination velocities for GaAs grown on a Si wafer using compositionally graded GeSi buffers have been investigated as a function of GaAs buffer thickness using monolayer-scale control of the GaAs/Ge interface nucleation during molecular beam epitaxy. The GaAs layers are free of antiphase domain disorder, with threading dislocation densities measured by etch pit density of 5x10 5 -2x10 6 cm -2 . Analysis indicates no degradation in either minority carrier lifetime or interface recombination velocity down to a GaAs buffer thickness of 0.1 μm. In fact, record high minority carrier lifetimes exceeding 10 ns have been obtained for GaAs on Si with a 0.1 μm GaAs buffer. Secondary ion mass spectroscopy reveals that cross diffusion of Ga, As, and Ge at the GaAs/Ge interface formed on the graded GeSi buffers are below detection limits in the interface region, indicating that polarity control of the GaAs/Ge interface formed on GeSi/Si substrates can be achieved. (c) 2000 American Institute of Physics

Three-dimensional lattice rotation in GaAs nanowire growth on hydrogen-silsesquioxane covered GaAs (001) using molecular beam epitaxy

Science.gov (United States)

Tran, Dat Q.; Pham, Huyen T.; Higashimine, Koichi; Oshima, Yoshifumi; Akabori, Masashi

2018-05-01

We report on crystallographic behaviors of inclined GaAs nanowires (NWs) self-crystallized on GaAs (001) substrate. The NWs were grown on hydrogen-silsesquioxane (HSQ) covered substrates using molecular beam epitaxy (MBE). Commonly, the epitaxial growth of GaAs B (B-polar) NWs is prominently observed on GaAs (001); however, we yielded a remarkable number of epitaxially grown GaAs A (A-polar) NWs in addition to the majorly obtained B-polar NWs. Such NW orientations are always accompanied by a typical inclined angle of 35° from (001) plane. NWs with another inclined angle of 74° were additionally observed and attributed to be -oriented, not in direct epitaxial relation with the substrate. Such 74° NWs' existence is related to first-order three-dimensional (3D) lattice rotation taking place at the very beginning of the growth. It turns out that spatially 60° lattice rotation around directions at GaAs seeds is essentially in charge of A- and B-polar 74° NWs. Transmission electron microscope observations reveal a high density of twinning in the B-polar NWs and twin-free characteristic in the A-polar NWs.

Polarization and charge limit studies of strained GaAs photocathodes

International Nuclear Information System (INIS)

Saez, P.J.

1997-03-01

This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of ∼ 2.5 A/cm 2 at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don't have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes

Collectively-enhanced optomechanical coupling in periodic arrays of scatterers

DEFF Research Database (Denmark)

Xuereb, André; Genes, Claudiu; Dantan, Aurelien Romain

2013-01-01

in linear optomechanical coupling strengths between the cavity field and collective motional modes of the array that may be several orders of magnitude larger than is possible with an equivalent reflective ensemble. We describe and interpret these effects in detail and investigate the nature of the scaling...... laws of the coupling strengths for the different transmissive points in various regimes....

Enhancing a slow and weak optomechanical nonlinearity with delayed quantum feedback

Science.gov (United States)

Wang, Zhaoyou; Safavi-Naeini, Amir H.

2017-07-01

A central goal of quantum optics is to generate large interactions between single photons so that one photon can strongly modify the state of another one. In cavity optomechanics, photons interact with the motional degrees of freedom of an optical resonator, for example, by imparting radiation pressure forces on a movable mirror or sensing minute fluctuations in the position of the mirror. Here, we show that the optical nonlinearity arising from these effects, typically too small to operate on single photons, can be sufficiently enhanced with feedback to generate large interactions between single photons. We propose a protocol that allows photons propagating in a waveguide to interact with each other through multiple bounces off an optomechanical system. The protocol is analysed by evolving the full many-body quantum state of the waveguide-coupled system, illustrating that large photon-photon interactions mediated by mechanical motion may be within experimental reach.

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Suzuki, Hidetoshi, E-mail: hsuzuki@cc.miyazaki-u.ac.jp [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen-Kibanadai-Nishi, Miyazaki 889-2192 (Japan); Nakata, Yuka; Takahasi, Masamitu [Graduate School of Materials Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Hyogo 678-1297 (Japan); Quantum Beam Science Center, Japan Atomic Energy Agency, 1-1-1 Koto, Sayo-cho, Hyogo 679-5148 (Japan); Ikeda, Kazuma [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Ohshita, Yoshio; Morohara, Osamu; Geka, Hirotaka; Moriyasu, Yoshitaka [Advanced Devices and Sensor Systems Development Center, Asahi Kasei Co. Ltd., 2-1 Samejima, Fuji 416-8501 (Japan)

2016-03-15

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

Quantum optomechanical piston engines powered by heat

Science.gov (United States)

Mari, A.; Farace, A.; Giovannetti, V.

2015-09-01

We study two different models of optomechanical systems where a temperature gradient between two radiation baths is exploited for inducing self-sustained coherent oscillations of a mechanical resonator. From a thermodynamic perspective, such systems represent quantum instances of self-contained thermal machines converting heat into a periodic mechanical motion and thus they can be interpreted as nano-scale analogues of macroscopic piston engines. Our models are potentially suitable for testing fundamental aspects of quantum thermodynamics in the laboratory and for applications in energy efficient nanotechnology.

Quantum optomechanical piston engines powered by heat

International Nuclear Information System (INIS)

Mari, A; Farace, A; Giovannetti, V

2015-01-01

We study two different models of optomechanical systems where a temperature gradient between two radiation baths is exploited for inducing self-sustained coherent oscillations of a mechanical resonator. From a thermodynamic perspective, such systems represent quantum instances of self-contained thermal machines converting heat into a periodic mechanical motion and thus they can be interpreted as nano-scale analogues of macroscopic piston engines. Our models are potentially suitable for testing fundamental aspects of quantum thermodynamics in the laboratory and for applications in energy efficient nanotechnology. (paper)

On the high characteristic temperature of an InAs/GaAs/InGaAsP QD laser with an emission wavelength of ~1.5 μm on an InP substrate

DEFF Research Database (Denmark)

Zubov, F.; Semenova, Elizaveta; Kulkova, Irina

2017-01-01

We report on a study of lasers with an emission wavelength of about 1.5 μm and high temperature stability, synthesized on an InP (001) substrate. Self-organized InAs quantum dots capped with a thin GaAs layer are used as the active region of the laser. A quaternary InGaAsP solid solution with a b......We report on a study of lasers with an emission wavelength of about 1.5 μm and high temperature stability, synthesized on an InP (001) substrate. Self-organized InAs quantum dots capped with a thin GaAs layer are used as the active region of the laser. A quaternary InGaAsP solid solution...

Nonperturbative Dynamical Casimir Effect in Optomechanical Systems: Vacuum Casimir-Rabi Splittings

Directory of Open Access Journals (Sweden)

Vincenzo Macrì

2018-02-01

Full Text Available We study the dynamical Casimir effect using a fully quantum-mechanical description of both the cavity field and the oscillating mirror. We do not linearize the dynamics, nor do we adopt any parametric or perturbative approximation. By numerically diagonalizing the full optomechanical Hamiltonian, we show that the resonant generation of photons from the vacuum is determined by a ladder of mirror-field vacuum Rabi splittings. We find that vacuum emission can originate from the free evolution of an initial pure mechanical excited state, in analogy with the spontaneous emission from excited atoms. By considering a coherent drive of the mirror, using a master-equation approach to take losses into account, we are able to study the dynamical Casimir effect for optomechanical coupling strengths ranging from weak to ultrastrong. We find that a resonant production of photons out of the vacuum can be observed even for mechanical frequencies lower than the cavity-mode frequency. Since high mechanical frequencies, which are hard to achieve experimentally, were thought to be imperative for realizing the dynamical Casimir effect, this result removes one of the major obstacles for the observation of this long-sought effect. We also find that the dynamical Casimir effect can create entanglement between the oscillating mirror and the radiation produced by its motion in the vacuum field, and that vacuum Casimir-Rabi oscillations can occur. Finally, we also show that all these findings apply not only to optomechanical systems, but also to parametric amplifiers operating in the fully quantum regime.

Structure and homoepitaxial growth of GaAs(6 3 1)

International Nuclear Information System (INIS)

Mendez-Garcia, V.H.; Ramirez-Arenas, F.J.; Lastras-Martinez, A.; Cruz-Hernandez, E.; Pulzara-Mora, A.; Rojas-Ramirez, J.S.; Lopez-Lopez, M.

2006-01-01

We have studied the surface atomic structure of GaAs(6 3 1), and the GaAs growth by molecular beam epitaxy (MBE) on this plane. After the oxide desorption process at 585 deg. Creflection high-energy electron diffraction (RHEED) showed along the [-1 2 0] direction a 2x surface reconstruction for GaAs(6 3 1)A, and a 1x pattern was observed for GaAs(6 3 1)B. By annealing the substrates for 60 min, we observed that on the A surface appeared small hilly-like features, while on GaAs(6 3 1)B surface pits were formed. For GaAs(6 3 1)A, 500 nm-thick GaAs layers were grown at 585 deg. C. The atomic force microscopy (AFM) images at the end of growth showed the self-formation of nanoscale structures with a pyramidal shape enlarged along the [5-9-3] direction. Transversal views of the bulk-truncated GaAs(6 3 1) surface model showed arrays of atomic grooves along this direction, which could influence the formation of the pyramidal structures

GaAs radiovoltaic cell enhanced by Y{sub 2}SiO{sub 5} crystal for the development of new gamma microbatteries

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zheng-Rong [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China); Tang, Xiao-Bin, E-mail: tangxiaobin@nuaa.edu.cn [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China); Jiangsu Key Laboratory of Material and Technology for Energy Conversion, Nanjing 211106 (China); Liu, Yun-Peng [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China); Jiangsu Key Laboratory of Material and Technology for Energy Conversion, Nanjing 211106 (China); Xu, Zhi-Heng; Yuan, Zi-Cheng; Liu, Kai; Chen, Wang [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China)

2017-05-01

Highlights: • A new gamma/GaAs multi-level structure radiovoltaic microbattery is proposed. • The properties of the new GaAs/YSO radiovoltaic cell was discussed. • The cell with Y{sub 2}SiO{sub 5} crystal can provide higher power and current output. • The irradiation resistance of Y{sub 2}SiO{sub 5} crystal under X-ray excitation was studied. - Abstract: The design of a new gamma/GaAs multi-level structure radiovoltaic microbattery enhanced by an Y{sub 2}SiO{sub 5} (YSO) crystal is proposed. By introducing the YSO crystal in the GaAs radiovoltaic cell, the output power from the cell was significantly improved. We focus on the enhancement mechanisms of performance output in one level of a multi-level structure. The radioluminescence spectra of the YSO crystal revealed its fluorescence in the wavelength range of approximately 300–700 nm. Light at the exact wavelength would normally be totally absorbed by the GaAs photovoltaic material. The radiovoltaic cells were tested using an X-ray tube to simulate the gamma rays emitted by a gamma-radioactive source. Experimental investigation showed that the YSO crystal can increase the cell output power. The output power of the new GaAs/YSO radiovoltaic cell was enhanced by more than four times compared to that of the conventional GaAs radiovoltaic cell. In addition, considering the importance of the YSO crystal in the new GaAs/YSO radiovoltaic cell, the irradiation resistance of the YSO crystal under X-ray excitation was also analysed.

The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study.

Science.gov (United States)

Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

2014-01-01

First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.

Subnanosecond linear GaAs photoconductive switching, revision 1

Science.gov (United States)

Druce, R. L.; Pocha, M. D.; Griffin, K. L.; Hofer, W. W.

Research was conducted in photoconductive switching for the purpose of generating subnanosecond pulses in the 25 to 50kV range. The very fast recombination rates of Gallium Arsenide (GaAs) was exploited to explore the potential of GaAs as a closing and opening switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). The closing time of a linear GaAs switch is theoretically limited by the characteristics of the laser pulse used to activate the switch (the carrier generation time in GaAs is (approx. 10(-14) sec) while the opening time is theoretically limited by the recombination time of the carriers. The recombination time is several ns for commercially available semi-insulating GaAs. Doping or neutron irradiation can reduce the recombination time to less than 100 ps. Switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps with neutron irradiated GaAs at fields of tens of kV/cm was observed. The illumination source was a Nd:YAG laser operating at 1.06 microns.

Acousto-optic modulation and opto-acoustic gating in piezo-optomechanical circuits

Science.gov (United States)

Balram, Krishna C.; Davanço, Marcelo I.; Ilic, B. Robert; Kyhm, Ji-Hoon; Song, Jin Dong; Srinivasan, Kartik

2017-01-01

Acoustic wave devices provide a promising chip-scale platform for efficiently coupling radio frequency (RF) and optical fields. Here, we use an integrated piezo-optomechanical circuit platform that exploits both the piezoelectric and photoelastic coupling mechanisms to link 2.4 GHz RF waves to 194 THz (1550 nm) optical waves, through coupling to propagating and localized 2.4 GHz acoustic waves. We demonstrate acousto-optic modulation, resonant in both the optical and mechanical domains, in which waveforms encoded on the RF carrier are mapped to the optical field. We also show opto-acoustic gating, in which the application of modulated optical pulses interferometrically gates the transmission of propagating acoustic pulses. The time-domain characteristics of this system under both pulsed RF and pulsed optical excitation are considered in the context of the different physical pathways involved in driving the acoustic waves, and modelled through the coupled mode equations of cavity optomechanics. PMID:28580373

Electrodeposition of Metal on GaAs Nanowires

Science.gov (United States)

Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

2010-10-01

Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

Diffusion of $^{52}$Mn in GaAs

CERN Multimedia

2002-01-01

Following our previous diffusion studies performed with the modified radiotracer technique, we propose to determine the diffusion of Mn in GaAs under intrinsic conditions in a previously un-investigated temperature region. The aim of the presently proposed experiments is twofold. \\begin{itemize} \\item A quantitative study of Mn diffusion in GaAs at low Mn concentrations would be decisive in providing new information on the diffusion mechanism involved. \\item As Ga vacancies are expected to be involved in the Mn diffusion process it can be predicted that also the GaAs material growth technique most likely plays a role. To clarify this assumption diffusion experiments will be conducted for GaAs material grown by two different techniques. \\end{itemize} For such experiments we ask for two runs of 3 shifts (total of 6 shifts) with $^{52}$Mn$^{+}$ ion beam.

Spatial confinement of acoustic and optical waves in stubbed slab structure as optomechanical resonator

Energy Technology Data Exchange (ETDEWEB)

Li, Changsheng, E-mail: lcs135@163.com; Huang, Dan; Guo, Jierong

2015-02-20

We theoretically demonstrate that acoustic waves and optical waves can be spatially confined in the same micro-cavity by specially designed stubbed slab structure. The proposed structure presents both phononic and photonic band gaps from finite element calculation. The creation of cavity mode inside the band gap region provides strong localization of phonon and photon in the defect region. The practical parameters to inject cavity and work experimentally at telecommunication range are discussed. This structure can be precisely fabricated, hold promises to enhance acousto-optical interactions and design new applications as optomechanical resonator. - Highlights: • A resonator simultaneously supports acoustic and optical modes. • Strong spatial confinement and slow group velocity. • Potential to work as active optomechanical resonator.

Building mechanical Greenberger-Horne-Zeilinger and cluster states by harnessing optomechanical quantum steerable correlations

Science.gov (United States)

Tan, Huatang; Wei, Yanghua; Li, Gaoxiang

2017-11-01

Greenberger-Horne-Zeilinger (GHZ) and cluster states are two typical kinds of multipartite entangled states and can respectively be used for realizing quantum networks and one-way computation. We propose a feasible scheme for generating Gaussian GHZ and cluster states of multiple mechanical oscillators by pulsed cavity optomechanics. In our scheme, each optomechanical cavity is driven by a blue-detuned pulse to establish quantum steerable correlations between the cavity output field and the mechanical oscillator, and the cavity outputs are combined at a beam-splitter array with given transmissivity and reflectivity for each beam splitter. We show that by harnessing the light-mechanical steerable correlations, the mechanical GHZ and cluster states can be realized via homodyne detection on the amplitude and phase quadratures of the output fields from the beam-splitter array. These achieved mechanical entangled states can be viewed as the output states of an effective mechanical beam-splitter array with the mechanical inputs prepared in squeezed states with the light-mechanical steering. The effects of detection efficiency and thermal noise on the achieved mechanical states are investigated. The present scheme does not require externally injected squeezing and it can also be applicable to other systems such as light-atomic-ensemble interface, apart from optomechanical systems.

GaAs FETs and novel heteroepitaxial quaternary lasers grown on InP substrates by organometallic chemical vapor deposition

International Nuclear Information System (INIS)

Lo, Y.H.; Bhat, R.; Chang-Hasnain, C.; Caneau, C.; Zah, C.E.; Lee, T.P.

1988-01-01

This paper reports the GaAs MESFETs and 1.3μm buried hetero-structure lasers with AlGaAs/GaAs lateral confinement layers simultaneously grown by OMCVD and fabricated on InP structures. The 1μm recessed gate MESFET has a transconductance of 220 mS/mm and the novel structured laser has a CW threshold current of 45 mA. The heteroepitaxy technology and devices show great promises for long wavelength opto-electronic integrated circuits

Subnanosecond linear GaAs photoconductive switching: Revision 1

Energy Technology Data Exchange (ETDEWEB)

Druce, R.L.; Pocha, M.D.; Griffin, K.L.; Hofer, W.W.

1989-01-01

We are conducting research in photoconductive switching for the purpose of generating subnanosecond pulses in the 25--50kV range. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as a closing and opening switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). The closing time of a linear GaAs switch is theoretically limited by the characteristics of the laser pulse used to activate the switch (the carrier generation time in GaAs is /approximately/10/sup /minus/14/ sec) while the opening time is theoretically limited by the recombination time of the carriers. The recombination time is several ns for commercially available semi-insulating GaAs. Doping or neutron irradiation can reduce the recombination time to less than 100 ps. We have observed switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps with neutron irradiated GaAs at fields of tens of kV/cm. The illumination source was a Nd:YAG laser operating at 1.06 /mu/m. 4 refs., 11 figs.

Imaging performance of a Timepix detector based on semi-insulating GaAs

Science.gov (United States)

Zaťko, B.; Zápražný, Z.; Jakůbek, J.; Šagátová, A.; Boháček, P.; Sekáčová, M.; Korytár, D.; Nečas, V.; Žemlička, J.; Mora, Y.; Pichotka, M.

2018-01-01

This work focused on a Timepix chip [1] coupled with a bulk semi-insulating GaAs sensor. The sensor consisted of a matrix of 256 × 256 pixels with a pitch of 55 μm bump-bonded to a Timepix ASIC. The sensor was processed on a 350 μm-thick SI GaAs wafer. We carried out detector adjustment to optimize its performance. This included threshold equalization with setting up parameters of the Timepix chip, such as Ikrum, Pream, Vfbk, and so on. The energy calibration of the GaAs Timepix detector was realized using a 241Am radioisotope in two Timepix detector modes: time-over-threshold and threshold scan. An energy resolution of 4.4 keV in FWHM (Full Width at Half Maximum) was observed for 59.5 keV γ-photons using threshold scan mode. The X-ray imaging quality of the GaAs Timepix detector was tested using various samples irradiated by an X-ray source with a focal spot size smaller than 8 μm and accelerating voltage up to 80 kV. A 700 μm × 700 μm gold testing object (X-500-200-16Au with Siemens star) fabricated with high precision was used for the spatial resolution testing at different values of X-ray image magnification (up to 45). The measured spatial resolution of our X-ray imaging system was about 4 μm.

Investigating the chemical and morphological evolution of GaAs capped InAs/InP quantum dots emitting at 1.5μm using aberration-corrected scanning transmission electron microscopy

DEFF Research Database (Denmark)

Kadkhodazadeh, Shima; Semenova, Elizaveta; Yvind, Kresten

2011-01-01

The emission wavelength of InAs quantum dots grown on InP has been shown to shift to the technologically desirable 1.5μm with the deposition of 1–2 monolayers of GaAs on top of the quantum dots. Here, we use aberration-corrected scanning transmission electron microscopy to investigate morphological...... and compositional changes occurring to the quantum dots as a result of the deposition of 1.7 monolayers of GaAs on top of them, prior to complete overgrowth with InP. The results are compared with theoretical models describing the overgrowth process....

Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field.

Science.gov (United States)

Ghali, Mohsen; Ohtani, Keita; Ohno, Yuzo; Ohno, Hideo

2012-02-07

Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.

Annealing-induced Fe oxide nanostructures on GaAs

OpenAIRE

Lu, Y X; Ahmad, E; Xu, Y B; Thompson, S M

2005-01-01

We report the evolution of Fe oxide nanostructures on GaAs(100) upon pre- and post-growth annealing conditions. GaAs nanoscale pyramids were formed on the GaAs surface due to wet etching and thermal annealing. An 8.0-nm epitaxial Fe film was grown, oxidized, and annealed using a gradient temperature method. During the process the nanostripes were formed, and the evolution has been demonstrated using transmission and reflection high energy electron diffraction, and scanning electron microscopy...

Demonstration of Efficient Nonreciprocity in a Microwave Optomechanical Circuit*

Science.gov (United States)

Peterson, G. A.; Lecocq, F.; Cicak, K.; Simmonds, R. W.; Aumentado, J.; Teufel, J. D.

2017-07-01

The ability to engineer nonreciprocal interactions is an essential tool in modern communication technology as well as a powerful resource for building quantum networks. Aside from large reverse isolation, a nonreciprocal device suitable for applications must also have high efficiency (low insertion loss) and low output noise. Recent theoretical and experimental studies have shown that nonreciprocal behavior can be achieved in optomechanical systems, but performance in these last two attributes has been limited. Here, we demonstrate an efficient, frequency-converting microwave isolator based on the optomechanical interactions between electromagnetic fields and a mechanically compliant vacuum-gap capacitor. We achieve simultaneous reverse isolation of more than 20 dB and insertion loss less than 1.5 dB. We characterize the nonreciprocal noise performance of the device, observing that the residual thermal noise from the mechanical environments is routed solely to the input of the isolator. Our measurements show quantitative agreement with a general coupled-mode theory. Unlike conventional isolators and circulators, these compact nonreciprocal devices do not require a static magnetic field, and they allow for dynamic control of the direction of isolation. With these advantages, similar devices could enable programmable, high-efficiency connections between disparate nodes of quantum networks, even efficiently bridging the microwave and optical domains.

Laser cooling of a harmonic oscillator's bath with optomechanics

Science.gov (United States)

Xu, Xunnong; Taylor, Jacob

Thermal noise reduction in mechanical systems is a topic both of fundamental interest for studying quantum physics at the macroscopic level and for application of interest, such as building high sensitivity mechanics based sensors. Similar to laser cooling of neutral atoms and trapped ions, the cooling of mechanical motion by radiation pressure can take single mechanical modes to their ground state. Conventional optomechanical cooling is able to introduce additional damping channel to mechanical motion, while keeping its thermal noise at the same level, and as a consequence, the effective temperature of the mechanical mode is lowered. However, the ratio of temperature to quality factor remains roughly constant, preventing dramatic advances in quantum sensing using this approach. Here we propose an efficient scheme for reducing the thermal load on a mechanical resonator while improving its quality factor. The mechanical mode of interest is assumed to be weakly coupled to its heat bath but strongly coupled to a second mechanical mode, which is cooled by radiation pressure coupling to a red detuned cavity field. We also identify a realistic optomechanical design that has the potential to realize this novel cooling scheme. Joint Center for Quantum Information and Computer Science, University of Maryland, College Park, MD 20742, USA.

Synthesis of GaAs quantum dots on Si-layers on AlGaAs films grown on GaAs(100) substrates

International Nuclear Information System (INIS)

Mendez-Garcia, V. H.; Zamora-Peredo, L.; Saucedo-Zeni, N.

2002-01-01

In this work we report a novel method for obtaining GaAs quantum dots by molecular beam epitaxy (MBE) on an AlGaAs underlying film. We propose to use a Si monolayer (ML) grown on AlGaAs, in order to induce a 3D nucleation during the GaAs overgrowth. The samples were prepared in a Riber 32P MBE system employing undoped Si-GaAs(100) substrates. First, a 500 nm thick layer of Al x Ga 1-x As was grown with a nominal concentration x=0.35. Several samples were grown in order to analyze the effects of changing the Si interlayer thickness, and the amount of GaAs overgrowth, on the final structures. Previous to the Si-exposure, the AlGaAs presented a (1x3) surface reconstruction which gradually turned to a (3x1) structure when the Si-thickness was 1 ML, as observed in the reflection high-energy electron diffraction (RHEED) patterns. When the GaAs overgrowth started on this surface, transmission RHEED spots appeared and showed a considerable increase in intensity until reaching a maximum. This behavior is typical from a 3D island growth. If the GaAs overgrowth continues, the initial streaky RHEED patterns recovered indicating a 2D-growth. Thus, we prepared a sample stopping the GaAs overgrowth at the time when the diffraction 3D spot reached the maximum intensity, equivalent to 2ML of GaAs. The sample surface was analyzed in air by atomic force microscopy (AFM). Islands of 1.5 nm-height and 20x20 nm of base were clearly observed, these dimensions are suitable for applications in quantum dots. (Authors)

Uncertainty contributions due to different measurement strategies applied to optomechanical hole plate

DEFF Research Database (Denmark)

Morace, Renate Erica; Hansen, Hans Nørgaard; De Chiffre, Leonardo

2003-01-01

The work described in this paper deals with influence parameters in optical measurements, with particular respect to the choice of measurement strategy, which strongly affects the results of measurement. In this investigation, an optomechanical hole plate developed by DTU was measured with an opt...

Effect on cavity optomechanics of the interaction between a cavity field and a one-dimensional interacting bosonic gas

International Nuclear Information System (INIS)

Sun Qing; Hu Xinghua; Liu, W. M.; Xie, X. C.; Ji Anchun

2011-01-01

We investigate optomechanical coupling between one-dimensional interacting bosons and the electromagnetic field in a high-finesse optical cavity. We show that by tuning interatomic interactions, one can realize effective optomechanics with mechanical resonators ranging from side-mode excitations of a Bose-Einstein condensate (BEC) to particle-hole excitations of a Tonks-Girardeau (TG) gas. We propose that this unique feature can be formulated to detect the BEC-TG gas crossover and measure the sine-Gordon transition continuously and nondestructively.

A chip-scale integrated cavity-electro-optomechanics platform

DEFF Research Database (Denmark)

Winger, M.; Blasius, T. D.; Mayer Alegre, T. P.

2011-01-01

We present an integrated optomechanical and electromechanical nanocavity, in which a common mechanical degree of freedom is coupled to an ultrahigh-Q photonic crystal defect cavity and an electrical circuit. The system allows for wide-range, fast electrical tuning of the optical nanocavity...... resonances, and for electrical control of optical radiation pressure back-action effects such as mechanical amplification (phonon lasing), cooling, and stiffening. These sort of integrated devices offer a new means to efficiently interconvert weak microwave and optical signals, and are expected to pave...

Diamond electro-optomechanical resonators integrated in nanophotonic circuits

Energy Technology Data Exchange (ETDEWEB)

Rath, P.; Ummethala, S.; Pernice, W. H. P., E-mail: wolfram.pernice@kit.edu [Institute of Nanotechnology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen (Germany); Diewald, S. [Center for Functional Nanostructures, Karlsruhe Institute of Technology, 76131 Karlsruhe (Germany); Lewes-Malandrakis, G.; Brink, D.; Heidrich, N.; Nebel, C. [Fraunhofer Institute for Applied Solid State Physics, Tullastr. 72, 79108 Freiburg (Germany)

2014-12-22

Diamond integrated photonic devices are promising candidates for emerging applications in nanophotonics and quantum optics. Here, we demonstrate active modulation of diamond nanophotonic circuits by exploiting mechanical degrees of freedom in free-standing diamond electro-optomechanical resonators. We obtain high quality factors up to 9600, allowing us to read out the driven nanomechanical response with integrated optical interferometers with high sensitivity. We are able to excite higher order mechanical modes up to 115 MHz and observe the nanomechanical response also under ambient conditions.

Injection locking of optomechanical oscillators via acoustic waves

Science.gov (United States)

Huang, Ke; Hossein-Zadeh, Mani

2018-04-01

Injection locking is a powerful technique for synchronization of oscillator networks and controlling the phase and frequency of individual oscillators using similar or other types of oscillators. Here, we present the first demonstration of injection locking of a radiation-pressure driven optomechanical oscillator (OMO) via acoustic waves. As opposed to previously reported techniques (based on pump modulation or direct application of a modulated electrostatic force), injection locking of OMO via acoustic waves does not require optical power modulation or physical contact with the OMO and it can easily be implemented on various platforms. Using this approach we have locked the phase and frequency of two distinct modes of a microtoroidal silica OMO to a piezoelectric transducer (PZT). We have characterized the behavior of the injection locked OMO with three acoustic excitation configurations and showed that even without proper acoustic impedance matching the OMO can be locked to the PZT and tuned over 17 kHz with only -30 dBm of RF power fed to the PZT. The high efficiency, simplicity and scalability of the proposed approach paves the road toward a new class of photonic systems that rely on synchronization of several OMOs to a single or multiple RF oscillators with applications in optical communication, metrology and sensing. Beyond its practical applications, injection locking via acoustic waves can be used in fundamental studies in quantum optomechanics where thermal and optical isolation of the OMO are critical.

Controlling the emission wavelength in group III-V semiconductor laser diodes

KAUST Repository

Ooi, Boon S.

2016-12-29

Methods are provided for modifying the emission wavelength of a semiconductor quantum well laser diode, e.g. by blue shifting the emission wavelength. The methods can be applied to a variety of semiconductor quantum well laser diodes, e.g. group III-V semiconductor quantum wells. The group III-V semiconductor can include AlSb, AlAs, Aln, AlP, BN, GaSb, GaAs, GaN, GaP, InSb, InAs, InN, and InP, and group III-V ternary semiconductors alloys such as AlxGai.xAs. The methods can results in a blue shifting of about 20 meV to 350 meV, which can be used for example to make group III-V semiconductor quantum well laser diodes with an emission that is orange or yellow. Methods of making semiconductor quantum well laser diodes and semiconductor quantum well laser diodes made therefrom are also provided.

Nested trampoline resonators for optomechanics

International Nuclear Information System (INIS)

Weaver, M. J.; Pepper, B.; Luna, F.; Perock, B.; Buters, F. M.; Eerkens, H. J.; Welker, G.; Heeck, K.; Man, S. de; Bouwmeester, D.

2016-01-01

Two major challenges in the development of optomechanical devices are achieving a low mechanical and optical loss rate and vibration isolation from the environment. We address both issues by fabricating trampoline resonators made from low pressure chemical vapor deposition Si 3 N 4 with a distributed Bragg reflector mirror. We design a nested double resonator structure with 80 dB of mechanical isolation from the mounting surface at the inner resonator frequency, and we demonstrate up to 45 dB of isolation at lower frequencies in agreement with the design. We reliably fabricate devices with mechanical quality factors of around 400 000 at room temperature. In addition, these devices were used to form optical cavities with finesse up to 181 000 ± 1000. These promising parameters will enable experiments in the quantum regime with macroscopic mechanical resonators

Nested trampoline resonators for optomechanics

Science.gov (United States)

Weaver, M. J.; Pepper, B.; Luna, F.; Buters, F. M.; Eerkens, H. J.; Welker, G.; Perock, B.; Heeck, K.; de Man, S.; Bouwmeester, D.

2016-01-01

Two major challenges in the development of optomechanical devices are achieving a low mechanical and optical loss rate and vibration isolation from the environment. We address both issues by fabricating trampoline resonators made from low pressure chemical vapor deposition Si3N4 with a distributed Bragg reflector mirror. We design a nested double resonator structure with 80 dB of mechanical isolation from the mounting surface at the inner resonator frequency, and we demonstrate up to 45 dB of isolation at lower frequencies in agreement with the design. We reliably fabricate devices with mechanical quality factors of around 400 000 at room temperature. In addition, these devices were used to form optical cavities with finesse up to 181 000 ± 1000. These promising parameters will enable experiments in the quantum regime with macroscopic mechanical resonators.

Computational study of GaAs1-xNx and GaN1-yAsy alloys and arsenic impurities in GaN

International Nuclear Information System (INIS)

Laaksonen, K; Komsa, H-P; Arola, E; Rantala, T T; Nieminen, R M

2006-01-01

We have studied the structural and electronic properties of As-rich GaAs 1-x N x and N-rich GaN 1-y As y alloys in a large composition range using first-principles methods. We have systematically investigated the effect of the impurity atom configuration near both GaAs and GaN sides of the concentration range on the total energies, lattice constants and bandgaps. The N (As) atoms, replacing substitutionally As (N) atoms in GaAs (GaN), cause the surrounding Ga atoms to relax inwards (outwards), making the Ga-N (Ga-As) bond length about 15% shorter (longer) than the corresponding Ga-As (Ga-N) bond length in GaAs (GaN). The total energies of the relaxed alloy supercells and the bandgaps experience large fluctuations within different configurations and these fluctuations grow stronger if the impurity concentration is increased. Substituting As atoms with N in GaAs induces modifications near the conduction band minimum, while substituting N atoms with As in GaN modifies the states near the valence band maximum. Both lead to bandgap reduction, which is at first rapid but later slows down. The relative size of the fluctuations is much larger in the case of GaAs 1-x N x alloys. We have also looked into the question of which substitutional site (Ga or N) As occupies in GaN. We find that under Ga-rich conditions arsenic prefers the substitutional N site over the Ga site within a large range of Fermi level values

Electrode pattern design for GaAs betavoltaic batteries

International Nuclear Information System (INIS)

Chen Haiyang; Yin Jianhua; Li Darang

2011-01-01

The sensitivities of betavoltaic batteries and photovoltaic batteries to series and parallel resistance are studied. Based on the study, an electrode pattern design principle of GaAs betavoltaic batteries is proposed. GaAs PIN junctions with and without the proposed electrode pattern are fabricated and measured under the illumination of 63 Ni. Results show that the proposed electrode can reduce the backscattering and shadowing for the beta particles from 63 Ni to increase the GaAs betavoltaic battery short circuit currents effectively but has little impact on the fill factors and ideal factors.

Opto-mechanical subsystem with temperature compensation through isothemal design

Science.gov (United States)

Goodwin, F. E. (Inventor)

1977-01-01

An opto-mechanical subsystem for supporting a laser structure which minimizes changes in the alignment of the laser optics in response to temperature variations is described. Both optical and mechanical structural components of the system are formed of the same material, preferably beryllium, which is selected for high mechanical strength and good thermal conducting qualities. All mechanical and optical components are mounted and assembled to provide thorough thermal coupling throughout the subsystem to prevent the development of temperature gradients.

Study of the energy band in n-type GaAs and p-type In P by transmission and photoluminescence spectroscopy

International Nuclear Information System (INIS)

Banai, N.; Khanzadeh, M.

1998-01-01

Optical characterization of the n-type In P grown by horizontal Bridgman method was carried out using modular photoluminescence and optical transmission spectroscopy. The measured transmission spectra at room temperature using Cary 17 DX spectrophotometer reveals the band gap energies of 1.4 and 1.34 eV for p-type In P and the n-type GaAs, respectively. Photoluminescence spectra of the above samples was measured at 77 K with the excitation intensity of (20 W/Cm 2 ). The (B-A) transitions occur at 1.405 eV and at 1.382 eV respectively. Three spectra were observed for the n-type GaAs sample, namely, (B-B), (B-A) and another relatively wide spectra at wavelengths above the absorption edge caused by the deep level impurities. The peak position of these spectra are 1.482, 1.4 and 1.36 eV respectively. (author)

Distinctions of the growth and structural-spectroscopic investigations of thin AlN films grown on the GaAs substrates

Science.gov (United States)

Seredin, P. V.; Kashkarov, V. M.; Arsentyev, I. N.; Bondarev, A. D.; Tarasov, I. S.

2016-08-01

Using X-ray diffraction analysis, atomic force microscopy, IR and UV spectroscopy, the properties of thin aluminium nitride films (4.0 for the wavelength band around 250 nm and an optical band-gap of 5 eV. It was shown that the morphology, surface composition and optical functional characteristics of AlN/GaAs heterophase systems can be controlled owing to the use of misoriented GaAs substrates as well choice of the technological parameters used for the film growth.

Self-Assembled Local Artificial Substrates of GaAs on Si Substrate

Directory of Open Access Journals (Sweden)

Frigeri C

2010-01-01

Full Text Available Abstract We propose a self-assembling procedure for the fabrication of GaAs islands by Droplet Epitaxy on silicon substrate. Controlling substrate temperature and amount of supplied gallium is possible to tune the base size of the islands from 70 up to 250 nm and the density from 107 to 109 cm−2. The islands show a standard deviation of base size distribution below 10% and their shape evolves changing the aspect ratio from 0.3 to 0.5 as size increases. Due to their characteristics, these islands are suitable to be used as local artificial substrates for the integration of III–V quantum nanostructures directly on silicon substrate.

Submicron resolution X-ray diffraction from periodically patterned GaAs nanorods grown onto Ge[111

Energy Technology Data Exchange (ETDEWEB)

Davydok, Anton; Biermanns, Andreas; Pietsch, Ullrich [Solid State Physics, Siegen University (Germany); Grenzer, Joerg [FZ-Dresden Rossendorf, Dresden (Germany); Paetzelt, Hendrik; Gottschalch, Volker; Bauer, Jens [Solid State Chemistry, University of Leipzig (Germany)

2009-08-15

We present high-resolution X-ray diffraction pattern of periodic GaAs nanorods (NRs) ensembles and individual GaAs NRs grown catalyst-free throughout a pre-patterned amorphous SiN{sub x} mask onto Ge[111]B surfaces by selective-area MOVPE method. To the best of our knowledge this is the first report about nano-structure X-ray characterization growth on non-polar substrate. The experiment has been performed at home laboratory and using synchrotron radiation using a micro-sized beam prepared by compound refractive lenses. Due to the non-polar character of the substrate the shapes of NRs appear not uniform and vary between deformed hexagonal and trigonal in symmetry. Because the average diameter of NRs equals the experimental resolution certain cuts through slightly inclined edges or corners of individual NRs with lateral size of about 225 nm could be selected using spatially resolved reciprocal space mapping. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

TEM study of the indentation behaviour of thin Au film on GaAs

International Nuclear Information System (INIS)

Patriarche, G.; Le Bourhis, E.; Faurie, D.; Renault, P.O.

2004-01-01

Au films of 8.9 nm thickness have been sputter deposited onto a (001) GaAs substrate at room temperature. An average grain size of 10 nm and no texture were obtained. Subsequent, nanoindentation tests were performed on the coated specimens and the mechanical response was compared to that of a bulk GaAs sample with the same crystallographic orientation. Furthermore, the loading-unloading curves were analysed in view of transmission electron microscopy plan-view images obtained on the deformed substrate-film specimens and compared to results previously reported in the literature for bulk sample. Constrained plasticity of the films was observed to occur for residual depth to thickness ratio below 0.67. Further, plastic deformation of the substrate happened on coated specimens at loads less than those required to plastically deform bare substrate

Double optomechanical transparency with direct mechanical interaction

International Nuclear Information System (INIS)

Li Ling-Chao; Shi Rao; Xu Jun; Hu Xiang-Ming

2015-01-01

We present a mechanism for double transparency in an optomechanical system. This mechanism is based on the coupling of a moving cavity mirror to a second mechanical oscillator. Due to the purely mechanical coupling and the radiation pressure, three pathways are established for excitations of the probe photons into the cavity photons. Destructive interference occurs at two different frequencies, leading to double transparency to the probe field. It is the coupling strength between the mechanical oscillators that determines the locations of the transparency windows. Moreover, the normal splitting appears for the generated Stokes field and the four-wave mixing process is inhibited on resonance. (paper)

Optimal estimation of the optomechanical coupling strength

Science.gov (United States)

Bernád, József Zsolt; Sanavio, Claudio; Xuereb, André

2018-06-01

We apply the formalism of quantum estimation theory to obtain information about the value of the nonlinear optomechanical coupling strength. In particular, we discuss the minimum mean-square error estimator and a quantum Cramér-Rao-type inequality for the estimation of the coupling strength. Our estimation strategy reveals some cases where quantum statistical inference is inconclusive and merely results in the reinforcement of prior expectations. We show that these situations also involve the highest expected information losses. We demonstrate that interaction times on the order of one time period of mechanical oscillations are the most suitable for our estimation scenario, and compare situations involving different photon and phonon excitations.

Increasing the quantum efficiency of GaAs solar cells by embedding InAs quantum dots

Science.gov (United States)

Salii, R. A.; Mintairov, S. A.; Nadtochiy, A. M.; Payusov, A. S.; Brunkov, P. N.; Shvarts, M. Z.; Kalyuzhnyy, N. A.

2016-11-01

Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).

Subnanosecond photoconductive switching in GaAs

Energy Technology Data Exchange (ETDEWEB)

Druce, R.L.; Pocha, M.D.; Griffin, K.L.

1991-04-01

We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in ``avalanche`` mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into ``avalanche`` mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

Subnanosecond photoconductive switching in GaAs

Energy Technology Data Exchange (ETDEWEB)

Druce, R.L.; Pocha, M.D.; Griffin, K.L.

1991-04-01

We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

Subnanosecond photoconductive switching in GaAs

Energy Technology Data Exchange (ETDEWEB)

Druce, R.L.; Pocha, M.D.; Griffin, K.L.

1990-01-01

We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential of GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into an avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large are (1 sq cm) and small area (<1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs., 11 figs.

Subnanosecond photoconductive switching in GaAs

Science.gov (United States)

Druce, R. L.; Pocha, M. D.; Griffin, K. L.

1991-04-01

We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in 'avalanche' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into 'avalanche' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (less than 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300-1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on, and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation.

Panel fabrication utilizing GaAs solar cells

Science.gov (United States)

Mardesich, N.

1984-01-01

The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

Atomic-scale structure of self-assembled In(Ga)As quantum rings in GaAs

NARCIS (Netherlands)

Offermans, P.; Koenraad, P.M.; Wolter, J.H.; Granados, D.; Garcia, J.M.; Fomin, V.; Gladilin, V.N.; Devreese, J.T.

2005-01-01

We present an atomic-scale analysis of the indium distribution of self-assembled In(Ga)As quantum rings (QRs) which are formed from InAs quantum dots by capping with a thin layer of GaAs and subsequent annealing. We find that the size and shape of QRs as observed by cross-sectional scanning

Nested trampoline resonators for optomechanics

Energy Technology Data Exchange (ETDEWEB)

Weaver, M. J., E-mail: mweaver@physics.ucsb.edu; Pepper, B.; Luna, F.; Perock, B. [Department of Physics, University of California, Santa Barbara, California 93106 (United States); Buters, F. M.; Eerkens, H. J.; Welker, G.; Heeck, K.; Man, S. de [Huygens-Kamerlingh Onnes Laboratorium, Universiteit Leiden, 2333 CA Leiden (Netherlands); Bouwmeester, D. [Department of Physics, University of California, Santa Barbara, California 93106 (United States); Huygens-Kamerlingh Onnes Laboratorium, Universiteit Leiden, 2333 CA Leiden (Netherlands)

2016-01-18

Two major challenges in the development of optomechanical devices are achieving a low mechanical and optical loss rate and vibration isolation from the environment. We address both issues by fabricating trampoline resonators made from low pressure chemical vapor deposition Si{sub 3}N{sub 4} with a distributed Bragg reflector mirror. We design a nested double resonator structure with 80 dB of mechanical isolation from the mounting surface at the inner resonator frequency, and we demonstrate up to 45 dB of isolation at lower frequencies in agreement with the design. We reliably fabricate devices with mechanical quality factors of around 400 000 at room temperature. In addition, these devices were used to form optical cavities with finesse up to 181 000 ± 1000. These promising parameters will enable experiments in the quantum regime with macroscopic mechanical resonators.

Preparation of GaAs photocathodes at low temperature

International Nuclear Information System (INIS)

Mulhollan, G.; Clendenin, J.; Tang, H.

1996-10-01

The preparation of an atomically clean surface is a necessary step in the formation of negative electron affinity (NEA) GaAs. Traditional methods to this end include cleaving, heat cleaning and epitaxial growth. Cleaving has the advantage of yielding a fresh surface after each cleave, but is limited to small areas and is not suitable for specialized structures. Heat cleaning is both simple and highly successful, so it is used as a preparation method in virtually all laboratories employing a NEA source on a regular basis. Due to its high cost and complexity, epitaxial growth of GaAs with subsequent in vacuo transfer is not a practical solution for most end users of GaAs as a NEA electron source. While simple, the heating cleaning process has a number of disadvantages. Here, a variety of cleaning techniques related to preparation of an atomically clean GaAs surface without heating to 600 C are discussed and evaluated

Superconductivity and its pressure variation in GaAs

International Nuclear Information System (INIS)

Nirmala Louis, C.; Jayam, Sr. Gerardin; Amalraj, A.

2005-01-01

The electronic band structure, metallization, phase transition and superconducting transition of gallium arsenide under pressure are studied using TB-LMTO method. Metallization occurs via indirect closing of band gap between Γ and X points. GaAs becomes superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The ground state properties are analyzed by fitting the calculated total energies to the Birch-Murnaghan's equation of state. The superconducting transition temperatures (T c ) obtained as a function of pressure for both the ZnS and NaCl structures and GaAs comes under the class of pressure induced superconductor. When pressure is increased T c increases in both the normal and high pressure structures. The dependence of T c on electron-phonon mass enhancement factor λ shows that GaAs is an electron-phonon-mediated superconductor. Also it is found that GaAs retained in their normal structure under high pressure give appreciably high T c . (author)

CIRP Interlaboratory Comparison of Coordinate Measuring Machines using an Optomechanical Hole Plate - Final Report

DEFF Research Database (Denmark)

De Chiffre, Leonardo; Hansen, Hans Nørgaard; Morace, Renata Erica

2005-01-01

be expected that the optomechanical hole plates can be calibrated using the DKD procedure with an uncertainty in the range between 0.5 µm and 2 µm. Using the hole plate, it is possible to compare the performance of measurements obtained using optical and mechanical CMMs. Optical CMM measurements can...... be divided in two groups. A group leading to deviations larger than 2 µm, and a group with deviations that are comparable to those using mechanical machines. All but one laboratory could perform reversal measurements. Transfer of traceability was established as follows: 8 using gauge blocks, 2 laser...... interferometers, 1 zerodur hole plate, 2 callipers, and 1 quartz standard. Out of the 23 measurement campaigns, 5 optical and 2 mechanical machines were not provided with establishment of traceability. The optomechanical hole plate is a suitable reference artefact providing traceability of CMMs, in particular...

Semi-insulating GaAs and Au Schottky barrier photodetectors for near-infrared detection (1280 nm)

Science.gov (United States)

Nusir, A. I.; Makableh, Y. F.; Manasreh, O.

2015-08-01

Schottky barriers formed between metal (Au) and semiconductor (GaAs) can be used to detect photons with energy lower than the bandgap of the semiconductor. In this study, photodetectors based on Schottky barriers were fabricated and characterized for the detection of light at wavelength of 1280 nm. The device structure consists of three gold fingers with 1.75 mm long and separated by 0.95 mm, creating an E shape while the middle finger is disconnected from the outer frame. When the device is biased, electric field is stretched between the middle finger and the two outermost electrodes. The device was characterized by measuring the current-voltage (I-V) curve at room temperature. This showed low dark current on the order of 10-10 A, while the photocurrent was higher than the dark current by four orders of magnitude. The detectivity of the device at room temperature was extracted from the I-V curve and estimated to be on the order of 5.3x1010 cm.Hz0.5/W at 5 V. The step response of the device was measured from time-resolved photocurrent curve at 5 V bias with multiple on/off cycles. From which the average recovery time was estimated to be 0.63 second when the photocurrent decreases by four orders of magnitude, and the average rise time was measured to be 0.897 second. Furthermore, the spectral response spectrum of the device exhibits a strong peak close to the optical communication wavelength (~1.3 μm), which is attributed to the internal photoemission of electrons above the Schottky barrier formed between Au and GaAs.

Effects of wavelength, beam type and size on cerebral low-level laser therapy by a Monte Carlo study on visible Chinese human

Directory of Open Access Journals (Sweden)

Ting Li

2015-01-01

Full Text Available Low-level laser therapy (LLLT has been clinically utilized for many indications in medicine requiring protection from cell/tissue death, stimulation of healing and repair of injuries, pain reduction, swelling and inflammation. Presently, the use of LLLT to treat stroke, traumatic brain injury and cognitive dysfunction are attracting growing interest. Near-infrared light is capable of penetrating into the cerebral cortex, allowing noninvasive treatments to be carried out with few treatment-related adverse events. Optimization of LLLT treatment effect is a crucial issue of this field; however, only a few experimental tests on mice for wavelength selection have been reported. We addressed this issue by low-cost, straightforward and quantitative comparisons on light dosage distribution within visible Chinese human head by Monte Carlo modeling of near-infrared light propagation. Optimized selection in wavelength, beam type and size were given based on comparisons among frequently used setups (i.e., wavelengths: 660, 810 and 980 nm; beam type: Gaussian and flat beam; beam diameter: 2, 4 and 6 cm. This study provided an efficient way for guiding the optimization of LLLT setup and selection on wavelength, beam type and size for clinical brain LLLT.

Comparisons of single event vulnerability of GaAs SRAMS

Science.gov (United States)

Weatherford, T. R.; Hauser, J. R.; Diehl, S. E.

1986-12-01

A GaAs MESFET/JFET model incorporated into SPICE has been used to accurately describe C-EJFET, E/D MESFET and D MESFET/resistor GaAs memory technologies. These cells have been evaluated for critical charges due to gate-to-drain and drain-to-source charge collection. Low gate-to-drain critical charges limit conventional GaAs SRAM soft error rates to approximately 1E-6 errors/bit-day. SEU hardening approaches including decoupling resistors, diodes, and FETs have been investigated. Results predict GaAs RAM cell critical charges can be increased to over 0.1 pC. Soft error rates in such hardened memories may approach 1E-7 errors/bit-day without significantly reducing memory speed. Tradeoffs between hardening level, performance and fabrication complexity are discussed.

Emission of circularly polarized recombination radiation from p-doped GaAs and GaAs0.62P0.38 under the impact of polarized electrons

International Nuclear Information System (INIS)

Fromme, B.; Baum, G.; Goeckel, D.; Raith, W.

1989-01-01

Circularly polarized light is emitted in radiative transitions of polarized electrons from the conduction to the valence band in GaAs or GaAs 1-x P x crystals. The degree of light polarization is directly related to the polarization of the conduction-band electrons at the instant of recombination and allows conclusions about the depolarization of electrons in the conduction band. The depolarization is caused by spin-relaxation processes. The efficiency of these processes depends on crystal type, crystal temperature, degree of doping, and kinetic energy of the electrons. Highly p-doped GaAs and GaAs 0.62 P 0.38 crystals (N A >1x10 19 atoms/cm 3 ) were bombarded with polarized electrons (initial polarization 38%), and the spectral distribution and the circular polarization of the emitted recombination radiation were measured. The initial kinetic energy of the electrons in the conduction band was varied between 5 and 1000 eV. The measurements of the spectral distribution show that the electrons are thermalized before recombination occurs, independent of their initial energy. An important thermalization process in this energy range is the excitation of crystal electrons by electron-hole pair creation. The circular polarization of the recombination radiation lies below 1% in the whole energy range. It decreases with increasing electron energy but is still of measurable magnitude at 100 eV in the case of GaAs 0.62 P 0.38 . The circular polarization is smaller for GaAs than for GaAs 0.62 P 0.38 , which we attribute to more efficient spin relaxation in GaAs

Wavelength-Dependent Extinction and Grain Sizes in "Dippers"

Science.gov (United States)

Sitko, Michael; Russell, Ray W.; Long, Zachary; Bayyari, Ammar; Assani, Korash; Grady, Carol; Lisse, Carey Michael; Marengo, Massimo; Wisniewski, John

2018-01-01

We have examined inter-night variability of K2-discovered "Dippers" that are not close to being viewed edge-on (as determined from previously-reported ALMA images) using the SpeX spectrograph on NASA's Infrared Telescope facility (IRTF). The three objects observed were EPIC 203850058, EPIC 205151387, and EPIC 204638512 ( = 2MASS J16042165-2130284). Using the ratio of the fluxes from 0.7-2.4 microns between two successive nights, we find that in at least two cases, the extinction increased toward shorter wavelengths. In the case of EPIC 204638512, we find that the properties of the dust differ from that seen in the diffuse interstellar medium and denser molecular clouds. However, the grain properties needed to explain the extinction does resemble those used to model the disks of many young stellar objects. The best fit to the data on EPIC 204638512 includes grains at least 500 microns in size, but lacks grains smaller than 0.25 microns. Since EPIC 204638512 is seen nearly face-on, it is possible the grains are entrained in an accretion flow that preferentially destroys the smallest grains. However, we have no indication of significant gas accretion onto the star in the form of emission lines observed in young low-mass stars. But the He I line at 1.083 microns was seen to change from night to night, and showed a P Cygni profile on one night, suggesting the gas might be outflowing from regions near the star.

Self-healing in fractured GaAs nanowires

International Nuclear Information System (INIS)

Wang Jun; Lu Chunsheng; Wang Qi; Xiao Pan; Ke Fujiu; Bai Yilong; Shen Yaogen; Wang Yanbo; Chen Bin; Liao Xiaozhou; Gao Huajian

2012-01-01

Molecular dynamics simulations are performed to investigate a spontaneous self-healing process in fractured GaAs nanowires with a zinc blende structure. The results show that such self-healing can indeed occur via rebonding of Ga and As atoms across the fracture surfaces, but it can be strongly influenced by several factors, including wire size, number of healing cycles, temperature, fracture morphology, oriented attachment and atomic diffusion. For example, it is found that the self-healing capacity is reduced by 46% as the lateral dimension of the wire increases from 2.3 to 9.2 nm, and by 64% after 24 repeated cycles of fracture and healing. Other factors influencing the self-healing behavior are also discussed.

Development of GaAs Detectors for Physics at the LHC

CERN Multimedia

Chu, Zhonghua; Krais, R; Rente, C; Syben, O; Tenbusch, F; Toporowsky, M; Xiao, Wenjiang; Cavallini, A; Fiori, F; Edwards, M; Geppert, R; Goppert, R; Haberla, C; Hornung, M F; Irsigler, R; Rogalla, M; Beaumont, S; Raine, C; Skillicorn, I; Margelevicius, J; Meshkinis, S; Smetana, S; Jones, B; Santana, J; Sloan, T; Zdansky, K; Alexiev, D; Donnelly, I J; Canali, C; Chiossi, C; Nava, F; Pavan, P; Kubasta, J; Tomiak, Z; Tchmil, V; Tchountonov, A; Tsioupa, I; Dogru, M; Gray, R; Hou, Yuqian; Manolopoulos, S; Walsh, S; Aizenshtadt, G; Budnitsky, D L; Gossen, A; Khludkov, S; Koretskaya, O B; Okaevitch, L; Potapov, A; Stepanov, V E; Tolbanov, O; Tyagev, A; Matulionis, A; Pozela, J; Kavaliauskiene, G; Kazukauskas, V; Kiliulis, R; Rinkevicius, V; Slenys, S; Storasta, J V

2002-01-01

% RD-8 Development of GaAs Detectors for Physics at the LHC \\\\ \\\\The aims of the collaboration are to investigate the available material options, performance and limitations of simple pad, pixel and microstrip GaAs detectors for minimum ionising particles with radiation hardness and speed which are competitive with silicon detectors. This new technology was originally developed within our university laboratories but now benefits from increasing industrial interest and collaboration in detector fabrication. Initial steps have also been taken towards the fabrication of GaAs preamplifiers to match the detectors in radiation hardness. The programme of work aims to construct a demonstration detector module for an LHC forward tracker based on GaAs.

Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

Directory of Open Access Journals (Sweden)

Takeo Ohno and Yutaka Oyama

2012-01-01

Full Text Available In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE, in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor.

WDM cross-connect cascade based on all-optical wavelength converters for routing and wavelength slot interchanging using a reduced number of internal wavelengths

DEFF Research Database (Denmark)

Pedersen, Rune Johan Skullerud; Mikkelsen, Benny; Jørgensen, Bo Foged

1998-01-01

interchanging can be used to create a robust and nonblocking OXC. However, for an OXC with n fiber inlets each carrying m wavelengths the OXC requires n×m internal wavelengths, which constrains the size of the cross-connect. In this paper we therefore propose and demonstrate an architecture that uses a reduced......Optical transport layers need rearrangeable wavelength-division multiplexing optical cross-connects (OXCs) to increase the capacity and flexibility of the network. It has previously been shown that a cross-connect based on all-optical wavelength converters for routing as well as wavelength slot...... set of internal wavelengths without sacrificing cross-connecting capabilities. By inserting a partly equipped OXC with the new architecture in a 10-Gbit/s re-circulating loop setup we demonstrate the possibility of cascading up to ten OXCs. Furthermore, we investigate the regenerating effect...

Dependence of ultrasound attenuation in rare earth metals on ratio of grain size and wavelength

International Nuclear Information System (INIS)

Kanevskij, I.N.; Nisnevich, M.M.; Spasskaya, A.A.; Kaz'mina, V.I.

1978-01-01

Results of investigation of dependences of ultrasound attenuation coefficient α on the ratio of grain average size D and wavelength lambda are presented. The investigations were carried out on rare earth metal samples produced by arc remelting in a vacuum furnace. It is shown that the way of α dependence curves of D/lambda for each of the rare earth metal is determined only by the D. This fact permits to use ultrasound measurement for control average diameter of the rare earth metal grain

A novel nano-sensor based on optomechanical crystal cavity

Science.gov (United States)

Zhang, Yeping; Ai, Jie; Ma, Jingfang

2017-10-01

Optical devices based on new sensing principle are widely used in biochemical and medical area. Nowadays, mass sensing based on monitoring the frequency shifts induced by added mass in oscillators is a well-known and widely used technique. It is interesting to note that for nanoscience and nanotechnology applications there is a strong demand for very sensitive mass sensors, being the target a sensor for single molecule detection. The desired mass resolution for very few or even single molecule detection, has to be below the femtogram range. Considering the strong interaction between high co-localized optical mode and mechanical mode in optomechanical crystal (OMC) cavities, we investigate OMC splitnanobeam cavities in silicon operating near at the 1550nm to achieve high optomechanical coupling rate and ultra-small motion mass. Theoretical investigations of the optical and mechanical characteristic for the proposed cavity are carried out. By adjusting the structural parameters, the cavity's effective motion mass below 10fg and mechanical frequency exceed 10GHz. The transmission spectrum of the cavity is sensitive to the sample which located on the center of the cavity. We conducted the fabrication and the characterization of this cavity sensor on the silicon-on-insulator (SOI) chip. By using vertical coupling between the tapered fiber and the SOI chip, we measured the transmission spectrum of the cavity, and verify this cavity is promising for ultimate precision mass sensing and detection.

X-ray characterization of Au-free grown GaAs nanowires on Si

Energy Technology Data Exchange (ETDEWEB)

Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Breuer, Steffen; Geelhaar, Lutz [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

2011-07-01

Semiconductor nanowires (NW) are of particular interest due to the ability to synthesize single-crystalline 1D epitaxial structures and heterostructures in the nanometer range. However, many details of the growth mechanism are not well understood. In this contribution we present a x-ray diffraction study of the early stage of Au-free GaAs nanowire growth on Si(111)-substrates with native oxide using the nano-focus setup available at the ID1 beamline of ESRF. The GaAs NWs were grown by molecular beam epitaxy (MBE), and their formation was induced by Ga droplets. Using a nanometer-sized x-ray beam, size and lattice parameters of individual wires were measured separately. Using asymmetric x-ray diffraction on particular zinc-blende (ZB) and wurtzite (W) sensitive reflections, we show that under the used conditions the NW growth starts with predominantly WZ phases and continues mainly in ZB phase. In addition we can show that the WZ segments of the NWs exhibit a different vertical lattice parameter compared to the zinc-blende segments. A combination of x-ray diffraction from single wires and grazing incidence diffraction shows that the base of the NW is compressively strained along the inplane direction. This strain is released within 20 nm from the substrate-interface.

35-kV GaAs subnanosecond photoconductive switches

Science.gov (United States)

Pocha, Michael D.; Druce, Robert L.

1990-12-01

High-voltage, fast-pulse generation using GaAs photoconductive switches is investigated. It is possible to to generate 35-kV pulses with risetimes as short as 135 ps using 5-mm gap switches, and electric field hold-off of greater than 100 kV/cm is achieved. An approximately 500-ps FWHM on/off electrical pulse is generated with an amplitude of approximately 3 kV using neutron-irradiated GaAs having short carrier lifetimes. Experimental results are described, and fabrication of switches and the diagnostics used to measure these fast signals are discussed. Experience with the nonlinear lock-on and avalanche modes of operation observed in GaAs is also described.

Status of fully integrated GaAs particle detectors

International Nuclear Information System (INIS)

Braunschweig, W.; Breibach, J.; Kubicki, Th.; Luebelsmeyer, K.; Maesing, Th.; Rente, C.; Roeper, Ch.; Siemes, A.

1999-01-01

GaAs strip detectors are of interest because of their radiation hardness at room temperature and the high absorption coefficient of GaAs for x-rays. The detectors currently under development will be used in the VLQ-experiment at the H1 experiment at the HERA collider. This will be the first high energy physics experiment where GaAs detectors will be used. The detectors have a sensitive area of 5 x 4 cm with a pitch of 62 μ m. Due to the high density of channels the biasing resistors and coupling capacitors are integrated. For the resistors a resistive layer made of Cermet is used. The properties of the first fully integrated strip detector are presented

GaAs droplet quantum dots with nanometer-thin capping layer for plasmonic applications

Science.gov (United States)

In Park, Suk; Trojak, Oliver Joe; Lee, Eunhye; Song, Jin Dong; Kyhm, Jihoon; Han, Ilki; Kim, Jongsu; Yi, Gyu-Chul; Sapienza, Luca

2018-05-01

We report on the growth and optical characterization of droplet GaAs quantum dots (QDs) with extremely-thin (11 nm) capping layers. To achieve such result, an internal thermal heating step is introduced during the growth and its role in the morphological properties of the QDs obtained is investigated via scanning electron and atomic force microscopy. Photoluminescence measurements at cryogenic temperatures show optically stable, sharp and bright emission from single QDs, at visible wavelengths. Given the quality of their optical properties and the proximity to the surface, such emitters are good candidates for the investigation of near field effects, like the coupling to plasmonic modes, in order to strongly control the directionality of the emission and/or the spontaneous emission rate, crucial parameters for quantum photonic applications.

Atomic hydrogen cleaning of GaAs photocathodes

International Nuclear Information System (INIS)

Poelker, M.; Price, J.; Sinclair, C.

1997-01-01

It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs

Normal-Mode Splitting in a Weakly Coupled Optomechanical System

Science.gov (United States)

Rossi, Massimiliano; Kralj, Nenad; Zippilli, Stefano; Natali, Riccardo; Borrielli, Antonio; Pandraud, Gregory; Serra, Enrico; Di Giuseppe, Giovanni; Vitali, David

2018-02-01

Normal-mode splitting is the most evident signature of strong coupling between two interacting subsystems. It occurs when two subsystems exchange energy between themselves faster than they dissipate it to the environment. Here we experimentally show that a weakly coupled optomechanical system at room temperature can manifest normal-mode splitting when the pump field fluctuations are antisquashed by a phase-sensitive feedback loop operating close to its instability threshold. Under these conditions the optical cavity exhibits an effectively reduced decay rate, so that the system is effectively promoted to the strong coupling regime.

Optical pumping of hot phonons in GaAs

International Nuclear Information System (INIS)

Collins, C.L.; Yu, P.Y.

1982-01-01

Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated

Generation and amplification of a high-order sideband induced by two-level atoms in a hybrid optomechanical system

Science.gov (United States)

Liu, Zeng-Xing; Xiong, Hao; Wu, Ying

2018-01-01

It is quite important to enhance and control the optomechanically induced high-order sideband generation to achieve low-power optical comb and high-sensitivity sensing with an integrable structure. Here we present and analyze a proposal for enhancement and manipulation of optical nonlinearity and high-order sideband generation in a hybrid atom-cavity optomechanical system that is coherently driven by a bichromatic input field consisting of a control field and a probe field and that works beyond the perturbative regime. Our numerical analysis with experimentally achievable parameters confirms that robust high-order sideband generation and typical spectral structures with nonperturbative features can be created even under weak driven fields. The dependence of the high-order sideband generation on the atomic parameters are also discussed in detail, including the decay rate of the atoms and the coupling parameter between the atoms and the cavity field. We show that the cutoff order as well as the amplitude of the higher-order sidebands can be well tuned by the atomic coupling strength and the atomic decay rate. The proposed mechanism of enhancing optical nonlinearity is quite general and can be adopted to optomechanical systems with different types of cavity.

Photovoltaic X-ray detectors based on epitaxial GaAs structures

Energy Technology Data Exchange (ETDEWEB)

Achmadullin, R.A. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Artemov, V.V. [Shubnikov Institute of Crystallography, Russian Academy of Sciences, 59 Leninski pr., Moscow B-333, 117333 (Russian Federation); Dvoryankin, V.F. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation)]. E-mail: vfd217@ire216.msk.su; Dvoryankina, G.G. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Dikaev, Yu.M. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Ermakov, M.G. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Ermakova, O.N. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Chmil, V.B. [Scientific State Center, High Energy Physics Institute, Protvino, Moscow region (Russian Federation); Holodenko, A.G. [Scientific State Center, High Energy Physics Institute, Protvino, Moscow region (Russian Federation); Kudryashov, A.A.; Krikunov, A.I.; Petrov, A.G.; Telegin, A.A. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Vorobiev, A.P. [Scientific State Center, High Energy Physics Institute, Protvino, Moscow region (Russian Federation)

2005-12-01

A new type of the photovoltaic X-ray detector based on epitaxial p{sup +}-n-n'-n{sup +} GaAs structures which provides a high efficiency of charge collection in the non-bias operation mode at room temperature is proposed. The GaAs epitaxial structures were grown by vapor-phase epitaxy on heavily doped n{sup +}-GaAs(1 0 0) substrates. The absorption efficiency of GaAs X-ray detector is discussed. I-V and C-V characteristics of the photovoltaic X-ray detectors are analyzed. The built-in electric field profiles in the depletion region of epitaxial structures are measured by the EBIC method. Charge collection efficiency to {alpha}-particles and {gamma}-radiation are measured. The application of X-ray detectors is discussed.

Periodic nanostructures fabricated on GaAs surface by UV pulsed laser interference

Energy Technology Data Exchange (ETDEWEB)

Zhang, Wei; Huo, Dayun; Guo, Xiaoxiang; Rong, Chen; Shi, Zhenwu, E-mail: zwshi@suda.edu.cn; Peng, Changsi, E-mail: changsipeng@suda.edu.cn

2016-01-01

Graphical abstract: - Highlights: • Periodic nanostructures were fabricated on GaAs wafers by four-beam laser interference patterning which have potential applications in many fields. • Significant different results were obtained on epi-ready and homo-epitaxial GaAs substrate surfaces. • Two-pulse patterning was carried out on homo-epitaxial GaAs substrate, a noticeable morphology transformation induced by the second pulse was observed. • Temperature distribution on sample surface as a function of time and position was calculated by solving the heat diffusion equations. The calculation agrees well with the experiment results. - Abstract: In this paper, periodic nanostructures were fabricated on GaAs wafers by four-beam UV pulsed laser interference patterning. Significant different results were observed on epi-ready and homo-epitaxial GaAs substrate surfaces, which suggests GaAs oxide layer has an important effect on pulsed laser irradiation process. In the case of two-pulse patterning, a noticeable morphology transformation induced by the second pulse was observed on homo-epitaxial GaAs substrate. Based on photo-thermal mode, temperature distribution on sample surface as a function of time and position was calculated by solving the heat diffusion equations.

Large size self-assembled quantum rings: quantum size effect and modulation on the surface diffusion.

Science.gov (United States)

Tong, Cunzhu; Yoon, Soon Fatt; Wang, Lijun

2012-09-24

We demonstrate experimentally the submicron size self-assembled (SA) GaAs quantum rings (QRs) by quantum size effect (QSE). An ultrathin In0.1 Ga0.9As layer with different thickness is deposited on the GaAs to modulate the surface nucleus diffusion barrier, and then the SA QRs are grown. It is found that the density of QRs is affected significantly by the thickness of inserted In0.1 Ga0.9As, and the diffusion barrier modulation reflects mainly on the first five monolayer . The physical mechanism behind is discussed. The further analysis shows that about 160 meV decrease in diffusion barrier can be achieved, which allows the SA QRs with density of as low as one QR per 6 μm2. Finally, the QRs with diameters of 438 nm and outer diameters of 736 nm are fabricated using QSE.

Mobility-lifetime product in epitaxial GaAs X-ray detectors

Energy Technology Data Exchange (ETDEWEB)

Sun, G.C. [GESEC R and D, Universite Pierre et Marie Curie, Bat.11, 140 rue de Lourmel, 75015 Paris (France)]. E-mail: guocsun@ccr.jussieu.fr; Zazoui, M. [LPMC, Faculte des Sciences et Techniques-Mohammedia, B.P. 146 Bd Hassan II, Mohammedia, Maroc (Morocco); Talbi, N. [Faculte des Sciences, Universite de Gabes, Route de Medenine, 6029 Gabes (Tunisia); Khirouni, K. [Faculte des Sciences, Universite de Gabes, Route de Medenine, 6029 Gabes (Tunisia); Bourgoin, J.C. [GESEC R and D, Universite Pierre et Marie Curie, Bat.11, 140 rue de Lourmel, 75015 Paris (France)

2007-04-01

Self-supported thick (200-500 {mu}m), non-intentionally doped, epitaxial GaAs layers are good candidates for X-ray imaging for the following reasons. Their electronic properties are homogeneous over large areas, they can be grown at low cost, the technology to realize pixel detectors of various size is standard, the defect concentration is low and the fluorescence yield is small. Here, we characterize the defects present in the material and evaluate the mobility-lifetime product, using Deep Level Transient Spectroscopy combined with current-voltage and charge collection measurements.

Selective Linear or Quadratic Optomechanical Coupling via Measurement

Directory of Open Access Journals (Sweden)

Michael R. Vanner

2011-11-01

Full Text Available The ability to engineer both linear and nonlinear coupling with a mechanical resonator is an important goal for the preparation and investigation of macroscopic mechanical quantum behavior. In this work, a measurement based scheme is presented where linear or square mechanical-displacement coupling can be achieved using the optomechanical interaction that is linearly proportional to the mechanical position. The resulting square-displacement measurement strength is compared to that attainable in the dispersive case that has a direct interaction with the mechanical-displacement squared. An experimental protocol and parameter set are discussed for the generation and observation of non-Gaussian states of motion of the mechanical element.

Phonon number measurements using single photon opto-mechanics

International Nuclear Information System (INIS)

Basiri-Esfahani, S; Akram, U; Milburn, G J

2012-01-01

We describe a system composed of two coupled optical cavity modes with a coupling modulated by a bulk mechanical resonator. In addition, one of the cavity modes is irreversibly coupled to a single photon source. Our scheme is an opto-mechanical realization of the Jaynes–Cummings model where the qubit is a dual rail optical qubit while the bosonic degree of freedom is a matter degree of freedom realized as the bulk mechanical excitation. We show the possibility of engineering phonon number states of the mechanical oscillator in such a system by computing the conditional state of the mechanics after successive photon counting measurements. (paper)

Implantation annealing in GaAs by incoherent light

International Nuclear Information System (INIS)

Davies, D.E.; Ryan, T.G.; Soda, K.J.; Comer, J.J.

1983-01-01

Implanted GaAs has been successfully activated through concentrating the output of quartz halogen lamps to anneal in times of the order of 1 sec. The resulting layers are not restricted by the reduced mobilities and thermal instabilities of laser annealed GaAs. Better activation can be obtained than with furnace annealing but this generally requires maximum temperatures >= 1050degC. (author)

Growth and characteristics of p-type doped GaAs nanowire

Science.gov (United States)

Li, Bang; Yan, Xin; Zhang, Xia; Ren, Xiaomin

2018-05-01

The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow. The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow. In addition, the I–V curves of GaAs NWs has been measured and the p-type dope concentration under the II/III ratio of 0.013 and 0.038 approximated to 1019–1020 cm‑3. Project supported by the National Natural Science Foundation of China (Nos. 61376019, 61504010, 61774021) and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Nos. IPOC2017ZT02, IPOC2017ZZ01).

The opto-mechanical design for GMOX: a next-generation instrument concept for Gemini

Science.gov (United States)

Smee, Stephen A.; Barkhouser, Robert; Robberto, Massimo; Ninkov, Zoran; Gennaro, Mario; Heckman, Timothy M.

2016-08-01

We present the opto-mechanical design of GMOX, the Gemini Multi-Object eXtra-wide-band spectrograph, a potential next-generation (Gen-4 #3) facility-class instrument for Gemini. GMOX is a wide-band, multi-object, spectrograph with spectral coverage spanning 350 nm to 2.4 um with a nominal resolving power of R 5000. Through the use of Digital Micromirror Device (DMD) technology, GMOX will be able to acquire spectra from hundreds of sources simultaneously, offering unparalleled flexibility in target selection. Utilizing this technology, GMOX can rapidly adapt individual slits to either seeing-limited or diffraction-limited conditions. The optical design splits the bandpass into three arms, blue, red, and near infrared, with the near-infrared arm being split into three channels covering the Y+J band, H band, and K band. A slit viewing camera in each arm provides imaging capability for target acquisition and fast-feedback for adaptive optics control with either ALTAIR (Gemini North) or GeMS (Gemini South). Mounted at the Cassegrain focus, GMOX is a large (1.3 m x 2.8 m x 2.0 m) complex instrument, with six dichroics, three DMDs (one per arm), five science cameras, and three acquisition cameras. Roughly half of these optics, including one DMD, operate at cryogenic temperature. To maximize stiffness and simplify assembly and alignment, the opto-mechanics are divided into three main sub-assemblies, including a near-infrared cryostat, each having sub-benches to facilitate ease of alignment and testing of the optics. In this paper we present the conceptual opto-mechanical design of GMOX, with an emphasis on the mounting strategy for the optics and the thermal design details related to the near-infrared cryostat.

Terahertz emission from semi-insulating GaAs with octadecanthiol-passivated surface

International Nuclear Information System (INIS)

Wu, Xiaojun; Xu, Xinlong; Lu, Xinchao; Wang, Li

2013-01-01

Terahertz (THz) emission from octadecanthiol (ODT) passivated (1 0 0) surface of the semi-insulating GaAs was measured, and compared with those from the native oxidized and the fresh surfaces. It was shown that the self-assembled ODT monolayer can stabilize the GaAs (1 0 0) surface, and maintain a THz surface emission 1.4 times as efficient as the native oxidized surface under equal conditions. Surface passivation can reduce the built-in electric field in the depletion region of the GaAs (1 0 0), resulting in the suppression of the THz radiation to a different extent. Oxidation of GaAs surface reduces the THz amplitude mainly in the low-frequency region. These results indicate that GaAs can be made a more effective THz source by choosing molecular passivation technique. Conversely, the THz emission features such as polarity, amplitude, and phase from molecule-passivated surfaces may be used to characterize the attached molecules.

Effect of GaAs interlayer thickness variations on the optical properties of multiple InAs QD structure

International Nuclear Information System (INIS)

Park, C.Y.; Park, K.W.; Kim, J.M.; Lee, Y.T.

2009-01-01

Multiple InAs/GaAs self-assembled quantum dots (QDs) with vertically stacked structure are grown by molecular beam epitaxy and the effects of GaAs interlayer thickness variation on optical properties are studied. The growth conditions are optimized by in-situ RHEED, AFM, and PL measurement. The five InAs QD layers are embedded in GaAs and Al0.3Ga0.7As layer. The PL intensity is increased with increasing GaAs interlayer thickness. The thin GaAs interlayer has strain field, the strain-induced intermixing of indium atoms in the InAs QDs (blue-shift) can overcompensate for the effect on the increased QD size (red-shift) (H. Heidemeyer et al. Appl. Phys. Lett. 80, 1544 (2002); T. Nakaoka et al. J. Appl. Phys. Lett. 96, 150 (2004)[1, 2], respectively). For the interlayer thickness larger than about 7 nm, the blue-shifts are correlated to the dominant high-energy excited state transitions due to the successive state filling of the ground and higher excited states in the QDs. The energy separation of double PL peaks, originated from two different excited states, was kept at around 50 meV at room temperature. A possible mechanism concerning this phenomenon is also discussed. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Resolving the mystery of milliwatt-threshold opto-mechanical self-oscillation in dual-nanoweb fiber

Directory of Open Access Journals (Sweden)

J. R. Koehler

2016-08-01

Full Text Available It is interesting to pose the question: How best to design an optomechanical device, with no electronics, optical cavity, or laser gain, that will self-oscillate when pumped in a single pass with only a few mW of single-frequency laser power? One might begin with a mechanically resonant and highly compliant system offering very high optomechanical gain. Such a system, when pumped by single-frequency light, might self-oscillate at its resonant frequency. It is well-known, however, that this will occur only if the group velocity dispersion of the light is high enough so that phonons causing pump-to-Stokes conversion are sufficiently dissimilar to those causing pump-to-anti-Stokes conversion. Recently it was reported that two light-guiding membranes 20 μm wide, ∼500 nm thick and spaced by ∼500 nm, suspended inside a glass fiber capillary, oscillated spontaneously at its mechanical resonant frequency (∼6 MHz when pumped with only a few mW of single-frequency light. This was surprising, since perfect Raman gain suppression would be expected. In detailed measurements, using an interferometric side-probing technique capable of resolving nanoweb movements as small as 10 pm, we map out the vibrations along the fiber and show that stimulated intermodal scattering to a higher-order optical mode frustrates gain suppression, permitting the structure to self-oscillate. A detailed theoretical analysis confirms this picture. This novel mechanism makes possible the design of single-pass optomechanical oscillators that require only a few mW of optical power, no electronics nor any optical resonator. The design could also be implemented in silicon or any other suitable material.

Photovoltaic Properties of p-Doped GaAs Nanowire Arrays Grown on n-Type GaAs(111)B Substrate

Science.gov (United States)

2010-01-01

We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For the best sample, the conversion efficiency of 1.65% and the fill factor of 25% are obtained. PMID:20672038

A Tunable Eight-Wavelength Terahertz Modulator Based on Photonic Crystals

Science.gov (United States)

Ji, K.; Chen, H.; Zhou, W.; Zhuang, Y.; Wang, J.

2017-11-01

We propose a tunable eight-wavelength terahertz modulator based on a structure of triple triangular lattice photonic crystals by using photonic crystals in the terahertz regime. The triple triangular lattice was formed by nesting circular, square, and triangular dielectric cylinders. Three square point defects were introduced into the perfect photonic crystal to produce eight defect modes. GaAs was used as the point defects to realize tunability. We used a structure with a reflecting barrier to achieve modulation at high transmission rate. The insertion loss and extinction ratio were 0.122 and 38.54 dB, respectively. The modulation rate was 0.788 dB. The performance of the eightwavelength terahertz modulator showed great potential for use in future terahertz communication systems.

A self-calibrating optomechanical force sensor with femtonewton resolution

International Nuclear Information System (INIS)

Melcher, John; Stirling, Julian; Pratt, Jon R.; Shaw, Gordon A.; Cervantes, Felipe Guzmán

2014-01-01

We report the development of an ultrasensitive optomechanical sensor designed to improve the accuracy and precision of force measurements with atomic force microscopy. The sensors reach quality factors of 4.3 × 10 6 and force resolution on the femtonewton scale at room temperature. Self-calibration of the sensor is accomplished using radiation pressure to create a reference force. Self-calibration enables in situ calibration of the sensor in extreme environments, such as cryogenic ultra-high vacuum. The senor technology presents a viable route to force measurements at the atomic scale with uncertainties below the percent level

A self-calibrating optomechanical force sensor with femtonewton resolution

Energy Technology Data Exchange (ETDEWEB)

Melcher, John, E-mail: john.melcher@nist.gov; Stirling, Julian; Pratt, Jon R.; Shaw, Gordon A. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Cervantes, Felipe Guzmán [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Joint Quantum Institute, University of Maryland, College Park, Maryland 20742 (United States)

2014-12-08

We report the development of an ultrasensitive optomechanical sensor designed to improve the accuracy and precision of force measurements with atomic force microscopy. The sensors reach quality factors of 4.3 × 10{sup 6} and force resolution on the femtonewton scale at room temperature. Self-calibration of the sensor is accomplished using radiation pressure to create a reference force. Self-calibration enables in situ calibration of the sensor in extreme environments, such as cryogenic ultra-high vacuum. The senor technology presents a viable route to force measurements at the atomic scale with uncertainties below the percent level.

Control of slow-to-fast light and single-to-double optomechanically induced transparency in a compound resonator system: A theoretical approach

Science.gov (United States)

Ziauddin; Rahman, Mujeeb ur; Ahmad, Iftikhar; Qamar, Sajid

2017-10-01

The transmission characteristics of probe light field is investigated theoretically in a compound system of two coupled resonators. The proposed system consisted of two high-Q Fabry-Perot resonators in which one of the resonators is optomechanical. Optomechanically induced transparency (OMIT), having relatively large window, is noticed via strong coupling between the two resonators. We investigate tunable switching from single to double OMIT by increasing amplitude of the pump field. We notice that, control of slow and fast light can be obtained via the coupling strength between the two resonators.

Noctilucent cloud particle size determination based on multi-wavelength all-sky analysis

Science.gov (United States)

Ugolnikov, Oleg S.; Galkin, Alexey A.; Pilgaev, Sergey V.; Roldugin, Alexey V.

2017-10-01

The article deals with the analysis of color distribution in noctilucent clouds (NLC) in the sky based on multi-wavelength (RGB) CCD-photometry provided with the all-sky camera in Lovozero in the north of Russia (68.0°N, 35.1°E) during the bright expanded NLC performance in the night of August 12, 2016. Small changes in the NLC color across the sky are interpreted as the atmospheric absorption and extinction effects combined with the difference in the Mie scattering functions of NLC particles for the three color channels of the camera. The method described in this paper is used to find the effective monodisperse radius of particles about 55 nm. The result of these simple and cost-effective measurements is in good agreement with previous estimations of comparable accuracy. Non-spherical particles, Gaussian and lognormal distribution of the particle size are also considered.

Tunable optical nonreciprocity and a phonon-photon router in an optomechanical system with coupled mechanical and optical modes

Science.gov (United States)

Li, Guolong; Xiao, Xiao; Li, Yong; Wang, Xiaoguang

2018-02-01

We propose a multimode optomechanical system to realize tunable optical nonreciprocity that has the prospect of making an optical diode for information technology. The proposed model consists of two subsystems, each of which contains two optical cavities, injected with a classical field and a quantum signal via a 50:50 beam splitter, and a mechanical oscillator, coupled to both cavities via optomechanical coupling. Meanwhile two cavities and an oscillator in a subsystem are respectively coupled to their corresponding cavities and an oscillator in the other subsystem. Our scheme yields nonreciprocal effects at different frequencies with opposite directions, but each effective linear optomechanical coupling can be controlled by an independent classical one-frequency pump. With this setup one is able to apply quantum states with large fluctuations, which extends the scope of applicable quantum states, and exploit the independence of paths. Moreover, the optimal frequencies for nonreciprocal effects can be controlled by adjusting the relevant parameters. We also exhibit the path switching of two directions, from a mechanical input to two optical output channels, via tuning the signal frequency. In experiment, the considered scheme can be tuned to reach small damping rates of the oscillators relative to those of the cavities, which is more practical and requires less power than in previous schemes.

Temperature dependent magnetic properties of the GaAs substrate of spin-LEDs

International Nuclear Information System (INIS)

Ney, A; Harris, J S Jr; Parkin, S S P

2006-01-01

The temperature dependence of the magnetization of a light emitting diode having a ferromagnetic contact (spin-LED) is measured from 2 to 300 K in magnetic fields from 30 to 70 kOe and it is found that it originates from the GaAs substrate. The magnetization of GaAs comprises a van Vleck-type paramagnetic contribution to the susceptibility which scales inversely with the band gap of the semiconductor. Thus, the temperature dependence of the band gap of GaAs accounts for the non-linear temperature dependent magnetic susceptibility of GaAs and thus, at large magnetic fields, for the spin-LED

Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

International Nuclear Information System (INIS)

Ma Xiangrong; Shi Wei; Ji Weili; Xue Hong

2011-01-01

A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch. (semiconductor devices)

Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

Science.gov (United States)

Xiangrong, Ma; Wei, Shi; Weili, Ji; Hong, Xue

2011-12-01

A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch.

Non-linear mixing in coupled photonic crystal nanobeam cavities due to cross-coupling opto-mechanical mechanisms

Energy Technology Data Exchange (ETDEWEB)

Ramos, Daniel, E-mail: daniel.ramos@csic.es; Frank, Ian W.; Deotare, Parag B.; Bulu, Irfan; Lončar, Marko [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

2014-11-03

We investigate the coupling between mechanical and optical modes supported by coupled, freestanding, photonic crystal nanobeam cavities. We show that localized cavity modes for a given gap between the nanobeams provide weak optomechanical coupling with out-of-plane mechanical modes. However, we show that the coupling can be significantly increased, more than an order of magnitude for the symmetric mechanical mode, due to optical resonances that arise from the interaction of the localized cavity modes with standing waves formed by the reflection from thesubstrate. Finally, amplification of motion for the symmetric mode has been observed and attributed to the strong optomechanical interaction of our hybrid system. The amplitude of these self-sustained oscillations is large enough to put the system into a non-linear oscillation regime where a mixing between the mechanical modes is experimentally observed and theoretically explained.

Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

Science.gov (United States)

Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

2004-09-01

In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

Scattering by non-spherical particles of size comparable to a wavelength - A new semi-empirical theory

Science.gov (United States)

Pollack, J. B.; Cuzzi, J. N.

1980-01-01

An approximate method is proposed for evaluating the interaction of randomly oriented, nonspherical particles with the total intensity component of electromagnetic radiation. When the particle size parameter, x, the ratio of particle circumference to wavelength, is less than some upper bound x(o) (about 5), Mie theory is used. For x greater than x(o), the interaction is divided into three components: diffraction, external reflection, and transmission. Physical optics theory is used to obtain the first of these components; geometrical optics theory is applied to the second; and a simple parameterization is employed for the third. The predictions of this theory are found to be in very good agreement with laboratory measurements for a wide variety of particle shapes, sizes, and refractive indexes. Limitations of the theory are also noted.

Sub-threshold wavelength splitting in coupled photonic crystal cavity arrays

DEFF Research Database (Denmark)

Schubert, Martin; Frandsen, Lars Hagedorn; Skovgård, Troels Suhr

Coupled photonic crystal (PhC) cavity arrays have recently been found to increase the output power of nanocavity lasers by coherent coupling of a large number of cavities [1]. We have measured the sub-threshold behaviour of such structures in order to gain better understanding of the mode structure....... PhC structures defined by circular holes placed in a quadratic lattice with pitch a=280 nm were fabricated in a GaAs membrane and cavity arrays were realized by introducing single missing holes with intracavity hole distances of two, three, five and seven holes. Arrays with different number...... of coupled cavities were fabricated and characterized using photoluminescence measurements of quantum dots embedded in the GaAs PhC membrane. Since the collection spot size was ~2.5 μm and therefore small compared to the arrays, spectra were taken at several positions of each array....

Photon counting microstrip X-ray detectors with GaAs sensors

Science.gov (United States)

Ruat, M.; Andrä, M.; Bergamaschi, A.; Barten, R.; Brückner, M.; Dinapoli, R.; Fröjdh, E.; Greiffenberg, D.; Lopez-Cuenca, C.; Lozinskaya, A. D.; Mezza, D.; Mozzanica, A.; Novikov, V. A.; Ramilli, M.; Redford, S.; Ruder, C.; Schmitt, B.; Shi, X.; Thattil, D.; Tinti, G.; Tolbanov, O. P.; Tyazhev, A.; Vetter, S.; Zarubin, A. N.; Zhang, J.

2018-01-01

High-Z sensors are increasingly used to overcome the poor efficiency of Si sensors above 15 keV, and further extend the energy range of synchrotron and FEL experiments. Detector-grade GaAs sensors of 500 μm thickness offer 98% absorption efficiency at 30 keV and 50% at 50 keV . In this work we assess the usability of GaAs sensors in combination with the MYTHEN photon-counting microstrip readout chip developed at PSI. Different strip length and pitch are compared, and the detector performance is evaluated in regard of the sensor material properties. Despite increased leakage current and noise, photon-counting strips mounted with GaAs sensors can be used with photons of energy as low as 5 keV, and exhibit excellent linearity with energy. The charge sharing is doubled as compared to silicon strips, due to the high diffusion coefficient of electrons in GaAs.

Long-wavelength photonic integrated circuits and avalanche photodetectors

Science.gov (United States)

Tsou, Yi-Jen D.; Zaytsev, Sergey; Pauchard, Alexandre; Hummel, Steve; Lo, Yu-Hwa

2001-10-01

Fast-growing internet traffic volume require high data communication bandwidth over longer distances. Access network bottlenecks put pressure on short-range (SR) telecommunication systems. To effectively address these datacom and telecom market needs, low-cost, high-speed laser modules at 1310 to 1550 nm wavelengths and avalanche photodetectors are required. The great success of GaAs 850nm VCSEls for Gb/s Ethernet has motivated efforts to extend VCSEL technology to longer wavelengths in the 1310 and 1550 nm regimes. However, the technological challenges associated with materials for long wavelength VCSELs are tremendous. Even with recent advances in this area, it is believed that significant additional development is necessary before long wavelength VCSELs that meet commercial specifications will be widely available. In addition, the more stringent OC192 and OC768 specifications for single-mode fiber (SMF) datacom may require more than just a long wavelength laser diode, VCSEL or not, to address numerous cost and performance issues. We believe that photonic integrated circuits (PICs), which compactly integrate surface-emitting lasers with additional active and passive optical components with extended functionality, will provide the best solutions to today's problems. Photonic integrated circuits have been investigated for more than a decade. However, they have produced limited commercial impact to date primarily because the highly complicated fabrication processes produce significant yield and device performance issues. In this presentation, we will discuss a new technology platform of InP-based PICs compatible with surface-emitting laser technology, as well as a high data rate externally modulated laser module. Avalanche photodetectors (APDs) are the key component in the receiver to achieve high data rate over long transmission distance because of their high sensitivity and large gain- bandwidth product. We have used wafer fusion technology to achieve In

Linearity of photoconductive GaAs detectors to pulsed electrons

International Nuclear Information System (INIS)

Ziegler, L.H.

1995-01-01

The response of neutron damaged GaAs photoconductor detectors to intense, fast (50 psec fwhm) pulses of 16 MeV electrons has been measured. Detectors made from neutron damaged GaAs are known to have reduced gain, but significantly improved bandwidth. An empirical relationship between the observed signal and the incident electron fluence has been determined

Wavelength scaling of laser plasma coupling

International Nuclear Information System (INIS)

Kruer, W.L.

1983-01-01

The use of shorter wavelength laser light both enhances collisional absorption and reduces deleterious collective plasma effects. Coupling processes which can be important in reactor-size targets are briefly reviewed. Simple estimates are presented for the intensity-wavelength regime in which collisional absorption is high and collective effects are minimized

Performance of a GaAs electron source

International Nuclear Information System (INIS)

Calabrese, R.; Ciullo, G.; Della Mea, G.; Egeni, G.P.; Guidi, V.; Lamanna, G.; Lenisa, P.; Maciga, B.; Rigato, V.; Rudello, V.; Tecchio, L.; Yang, B.; Zandolin, S.

1994-01-01

We discuss the performance improvement of a GaAs electron source. High quantum yield (14%) and constant current extraction (1 mA for more than four weeks) are achieved after a little initial decay. These parameters meet the requirements for application of the GaAs photocathode as a source for electron cooling devices. We also present the preliminary results of a surface analysis experiment, carried out by means of the RBS technique to check the hypothesis of cesium evaporation from the surface when the photocathode is in operation. (orig.)

Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

Energy Technology Data Exchange (ETDEWEB)

Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F. [University of Tsukuba, Institute of Applied Physics, Tsukuba, Ibaraki 305-8573 (Japan)

2004-09-01

In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerance of GaAs and that Ti can protected GaAs from erosion by NH{sub 3}. By depositing Ti on GaAs(111)A surface, a mirror-like GaN layer could be grown at 1000 C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Optomechanically induced transparency in multi-cavity optomechanical system with and without one two-level atom.

Science.gov (United States)

Sohail, Amjad; Zhang, Yang; Zhang, Jun; Yu, Chang-Shui

2016-06-28

We analytically study the optomechanically induced transparency (OMIT) in the N-cavity system with the Nth cavity driven by pump, probing laser fields and the 1st cavity coupled to mechanical oscillator. We also consider that one atom could be trapped in the ith cavity. Instead of only illustrating the OMIT in such a system, we are interested in how the number of OMIT windows is influenced by the cavities and the atom and what roles the atom could play in different cavities. In the resolved sideband regime, we find that, the number of cavities precisely determines the maximal number of OMIT windows. It is interesting that, when the two-level atom is trapped in the even-labeled cavity, the central absorptive peak (odd N) or dip (even N) is split and forms an extra OMIT window, but if the atom is trapped in the odd-labeled cavity, the central absorptive peak (odd N) or dip (even N) is only broadened and thus changes the width of the OMIT windows rather than induces an extra window.

Electrochemical formation of GaAs honeycomb structure using a fluoride-containing (NH{sub 4}){sub 2}SO{sub 4} solution

Energy Technology Data Exchange (ETDEWEB)

Morishita, Yoshitaka, E-mail: morisita@cc.tuat.ac.jp; Yamamoto, Hitoshi; Yokobori, Kuniyuki

2014-04-01

GaAs substrates were anodized in the (NH{sub 4}){sub 2}SO{sub 4} electrolyte with various fluoride concentrations. Scanning electron microscope (SEM) observation showed that highly regular honeycomb hollows were formed on the substrates anodized in the (NH{sub 4}){sub 2}SO{sub 4} electrolyte with a small amount of HF concentration. The regularity of hollows decreased with the increase of HF concentration. The average diameter of hollows increased with increasing anodizing voltage. The regularity of hollow diameters increased with the increase of anodizing time, irrespective of the anodizing voltage. Cross-sectional SEM image showed that the average depth of regular hollows was about 5 nm. In addition to the peak in the region of fundamental adsorption of GaAs with the peak wavelength at about 870 nm, photoluminescence spectra of samples anodized in the (NH{sub 4}){sub 2}SO{sub 4} electrolyte with HF concentration of 0.5 ml showed several peaks at about 610, 635, 670 and 720 nm. - Highlights: • We report on the electrochemical formation of GaAs honeycomb structure. • High regular hollows were formed by anodization in HF-containing (NH{sub 4}){sub 2}SO{sub 4} solution. • A thin porous layer was formed by anodization in HF-containing (NH{sub 4}){sub 2}SO{sub 4} solution. • This process is useful for preparing patterned substrate with a thin porous layer.

Nanoscale interfacial engineering to grow Ge on Si as virtual substrates and subsequent integration of GaAs

International Nuclear Information System (INIS)

Leonhardt, Darin; Sheng, Josephine; Cederberg, Jeffrey G.; Li Qiming; Carroll, Malcolm S.; Han, Sang M.

2010-01-01

We have demonstrated the scalability of a process previously dubbed as Ge 'touchdown' on Si to substantially reduce threading dislocations below 10 7 /cm 2 in a Ge film grown on a 2 inch-diameter chemically oxidized Si substrate. This study also elucidates the overall mechanism of the touchdown process. The 1.4 nm thick chemical oxide is first formed by immersing Si substrates in a solution of H 2 O 2 and H 2 SO 4 . Subsequent exposure to Ge flux creates 3 to 7 nm-diameter voids in the oxide at a density greater than 10 11 /cm 2 . Comparison of data taken from many previous studies and ours shows an exponential dependence between oxide thickness and inverse temperature of void formation. Additionally, exposure to a Ge or Si atom flux decreases the temperature at which voids begin to form in the oxide. These results strongly suggest that Ge actively participates in the reaction with SiO 2 in the void formation process. Once voids are created in the oxide under a Ge flux, Ge islands selectively nucleate within the void openings on the newly exposed Si. Island nucleation and growth then compete with the void growth reaction. At substrate temperatures between 823 and 1053 K, nanometer size Ge islands that nucleate within the voids continue to grow and coalesce into a continuous film over the remaining oxide. Coalescence of the Ge islands is believed to result in the creation of stacking faults in the Ge film at a density of 5 x 10 7 /cm 2 . Additionally, coalescence results in films of 3 μm thickness having a root-mean-square roughness of 8 to 10 nm. We have found that polishing the films with dilute H 2 O 2 results in roughness values below 0.5 nm. However, stacking faults originating at the Ge-SiO 2 interface and terminating at the Ge surface are polished at a slightly reduced rate, and show up as 1 to 2 nm raised lines on the polished Ge surface. These lines are then transferred into the subsequent growth morphology of GaAs deposited by metal-organic chemical vapor

Analysis and modelling of GaN Schottky-based circuits at millimeter wavelengths

International Nuclear Information System (INIS)

Pardo, D; Grajal, J

2015-01-01

This work presents an analysis of the capabilities of GaN Schottky diodes for frequency multipliers and mixers at millimeter wavelengths. By using a Monte Carlo (MC) model of the diode coupled to a harmonic balance technique, the electrical and noise performances of these circuits are investigated. Despite the lower electron mobility of GaN compared to GaAs, multipliers based on GaN Schottky diodes can be competitive in the first stages of multiplier chains, due to the excellent power handling capabilities of this material. The performance of these circuits can be improved by taking advantage of the lateral Schottky diode structures based on AlGaN/GaN HEMT technology. (paper)

Opto-mechanical design of an image slicer for the GRIS spectrograph at GREGOR

Science.gov (United States)

Vega Reyes, N.; Esteves, M. A.; Sánchez-Capuchino, J.; Salaun, Y.; López, R. L.; Gracia, F.; Estrada Herrera, P.; Grivel, C.; Vaz Cedillo, J. J.; Collados, M.

2016-07-01

An image slicer has been proposed for the Integral Field Spectrograph [1] of the 4-m European Solar Telescope (EST) [2] The image slicer for EST is called MuSICa (Multi-Slit Image slicer based on collimator-Camera) [3] and it is a telecentric system with diffraction limited optical quality offering the possibility to obtain high resolution Integral Field Solar Spectroscopy or Spectro-polarimetry by coupling a polarimeter after the generated slit (or slits). Considering the technical complexity of the proposed Integral Field Unit (IFU), a prototype has been designed for the GRIS spectrograph at GREGOR telescope at Teide Observatory (Tenerife), composed by the optical elements of the image slicer itself, a scanning system (to cover a larger field of view with sequential adjacent measurements) and an appropriate re-imaging system. All these subsystems are placed in a bench, specially designed to facilitate their alignment, integration and verification, and their easy installation in front of the spectrograph. This communication describes the opto-mechanical solution adopted to upgrade GRIS while ensuring repeatability between the observational modes, IFU and long-slit. Results from several tests which have been performed to validate the opto-mechanical prototypes are also presented.

Lightweight, Light-Trapped, Thin GaAs Solar Cells for Spacecraft Applications.

Science.gov (United States)

1995-10-05

improve the efficiency of this type of cell. 2 The high efficiency and light weight of the cover glass supported GaAs solar cell can have a significant...is a 3-mil cover glass and 1-mil silicone adhesive on the front surface of the GaAs solar cell. Power Output 3000 400 -{ 2400 { N 300 S18200 W/m2...the ultra-thin, light-trapped GaAs solar ceill 3. Incorporate light trapping. 0 external quantum efficiency at 850 nm increased by 5.2% 4. Develop

The GaAs electron source: simulations and experiments

International Nuclear Information System (INIS)

Aleksandrov, A.V.; Ciullo, G.; Guidi, V.; Kudelainen, V.I.; Lamanna, G.; Lenisa, P.; Logachov, P.V.; Maciga, B.; Novokhatsky, A.; Tecchio, L.; Yang, B.

1994-01-01

In this paper we calculate electron emission from GaAs photocathodes using the Monte Carlo technique. Typical data of energy spread of the electron beam are presented. For photoenergy ranging from 1.6 to 2.1 eV, the calculated longitudinal and transverse energy spreads are 14.4-78 and 4-14.7 meV respectively. Temporal measurement of GaAs photocathodes has been performed. The preliminary results show that the temporal response is faster than 200 ps. (orig.)

35-kV GaAs subnanosecond photoconductive switches

Energy Technology Data Exchange (ETDEWEB)

Pocha, M.D.; Druce, R.L. (Lawrence Livermore National Lab., CA (United States))

1990-12-01

Photoconductive switches are one of the few devices that allow the generation of high-voltage electrical pulses with subnanosecond rise time. The authors are exploring high-voltage, fast-pulse generation using GaAs photoconductive switches. They have been able to generate 35-kV pulses with rise times as short as 135 ps using 5-mm gap switches and have achieved electric field hold-off of greater than 100 kV/cm. They have also been able to generate an approximately 500-ps FWHM on/off electrical pulse with an amplitude of approximately 3 kV using neutron-irradiated GaAs having short carrier life times. This paper describes the experimental results and discusses fabrication of switches and the diagnostics used to measure these fast signals. They also describe the experience with the nonlinear lock-on and avalanche modes of operation observed in GaAs.

Structural Evolution During Formation and Filling of Self-patterned Nanoholes on GaAs (100 Surfaces

Directory of Open Access Journals (Sweden)

Zhou Lin

2008-01-01

Full Text Available Abstract Nanohole formation on an AlAs/GaAs superlattice gives insight to both the “drilling” effect of Ga droplets on AlAs as compared to GaAs and the hole-filling process. The shape and depth of the nanoholes formed on GaAs (100 substrates has been studied by the cross-section transmission electron microscopy. The Ga droplets “drill” through the AlAs layer at a much slower rate than through GaAs due to differences in activation energy. Refill of the nanohole results in elongated GaAs mounds along the [01−1] direction. As a result of capillarity-induced diffusion, GaAs favors growth inside the nanoholes, which provides the possibility to fabricate GaAs and AlAs nanostructures.

Electrical performance of conducting polymer (SPAN) grown on GaAs with different substrate orientations

Science.gov (United States)

Jameel, D. A.; Aziz, M.; Felix, J. F.; Al Saqri, N.; Taylor, D.; Albalawi, H.; Alghamdi, H.; Al Mashary, F.; Henini, M.

2016-11-01

This article reports the effect of n-type GaAs substrate orientation, namely (100), (311)A and (311)B, on the electrical properties of sulfonated polyaniline (SPAN)/GaAs heterojunction devices. In addition, the inhomogeneity of the interface between various GaAs substrates and SPAN is investigated in terms of barrier height and ideality factor by performing I-V measurements at different temperatures (20-420 K). The I-V results indicate that the value of the rectification ratio (IF/IR) at 0.5 V is higher for SPAN/(311)B GaAs samples than for SPAN/(100) GaAs and SPAN/(311)A GaAs samples. Moreover, the barrier height decreases and the ideality factor increases with decreasing temperature for all three heterostructure devices. The high value of mean barrier Φbarb of SPAN/(311)B (calculated from the plots of Φb 0 as a function of 1/2kT) confirms that the GaAs substrate orientation results in an increase of barrier homogeneities. Furthermore, the C-V characteristics were obtained at room temperature. The C-V measurements showed that the carrier distributions at the interface and away from the interface in high index (311) GaAs orientations are more uniform and have better barrier homogeneity than those grown on the conventional (100) GaAs substrates.

Quantum opto-mechanics with micromirrors : combining nano-mechanics with quantum optics

International Nuclear Information System (INIS)

Groeblacher, S.

2010-01-01

This work describes more than four years of research on the effects of the radiation-pressure force of light on macroscopic mechanical structures. The basic system studied here is a mechanical oscillator that is highly reflective and part of an optical resonator. It interacts with the optical cavity mode via the radiation-pressure force. Both the dynamics of the mechanical oscillation and the properties of the light field are modified through this interaction. In our experiments we use quantum optical tools (such as homodyning and down-conversion) with the goal of ultimately showing quantum behavior of the mechanical center of mass motion. In this thesis we present several experiments that pave the way towards this goal and when combined should allow the demonstration of the envisioned quantum phenomena, including entanglement, teleportation and Schroeodinger cat states. The study of quantum behavior of truly macroscopic systems is a long outstanding goal, which will help to answer some of the most fundamental questions in quantum physics today: Why is the world around us classical and not quantum? Is there a size- or mass-limit to systems for them to behave according to quantum mechanics? Is quantum theory complete or do we have to extend it to include mechanisms such as decoherence? Can we use the quantum nature of macroscopic objects to, for example, improve the measurement precision of classical apparatuses? The experiments discussed in this thesis include the very first passive radiation-pressure cooling of a mechanical oscillator in a cryogenic optical resonator, as well as the experimental demonstration of radiation-pressure cooling close to the mechanical quantum ground state. Cooling of the mechanical motion is an important pre-condition for observing quantum effects of the mechanical oscillator. In another experiment, we have demonstrated that we are able to enter the strong-coupling regime of the optomechanical system a regime where coherent energy

Effect of e-beam dose on the fractional density of Au-catalyzed GaAs nanowire growth

Energy Technology Data Exchange (ETDEWEB)

Park, Jeung Hun, E-mail: jeunghunpark@gmail.com [Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, CA 90095 (United States); Gambin, Vincent [Northrop Grumman Aerospace Systems, Redondo Beach, CA 90278 (United States); Kodambaka, Suneel, E-mail: kodambaka@ucla.edu [Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, CA 90095 (United States)

2016-05-31

Using Au/GaAs as a model system, the effect of initial catalyst patterning conditions on the growth of nanowire was studied. Resulting morphologies and fractional surface densities are determined as a function of e-beam dose, dot size, and inter-dot spacing using scanning and transmission electron microscopies. The majority of resulting nanowires grow randomly oriented with respect to the substrate. The nanowires are tapered with narrow tops, wider bases, and catalysts at the wire tips — characteristics of vapor–liquid–solid process. The base diameters of the wires are larger than the dot size, which is likely due to the non-catalyzed vapor–solid deposition along the sidewalls. The higher dose rate used in pattering leads to the formation of higher aspect ratio nanowires with narrower bases. The fractional surface density is found to increase linearly with the clearing dose and the critical dose for nanowire growth increases with decreasing catalyst pattern size and spacing. At a given dose, the fractional density increases with increasing Au dot size and with decreasing inter-dot spacing. Our results may provide new insights into the role of catalyst preparing conditions on the high density, wafer-scale growth of nanowires. - Highlights: • Initial Au catalyst layers are prepared using electron beam lithography. • GaAs nanowires are grown on GaAs(111)B using molecular beam epitaxy. • Effect of dose, size and spacing of Au dots on morphology and density is studied. • Density of nanowires is controlled by changing exposed dose on Au catalyst.

First principles study of the electronic and optical properties of GaAs nanoparticles under the influence of external uniform electric field

International Nuclear Information System (INIS)

Bezi Javan, Masoud

2012-01-01

We present electronic and optical properties of the hydrogen terminated gallium arsenide nanoparticles using time dependent density functional theory (TD-DFT). The electronic and optical properties of the GaAs nanoparticles were calculated at presence of the uniform external electric field in the range from 0 to 0.51 V/Å. The induced electric filed can decrease the HOMO–LUMO gap of the nanoparticles and the mount of these reductions increases with gain of the electric field strength. -- Highlights: ► HOMO–LUMO gap of the nanoparticles is significantly more than GaAs bulk band gap. ► HOMO–LUMO gap of the nanoparticles decreases with increase of the nanoparticles size. ► External electric filed decrease the HOMO–LUMO gap of the nanoparticles. ► Dipole moment of nanoparticles increases with gain of the electric field strength. ► Absorption peaks of GaAs nanoparticles shows red shift with applying electric field.

GaAs strip detectors: the Australian production program

International Nuclear Information System (INIS)

Butcher, K.S.A.; Alexiev, D.

1995-01-01

The Australian High Energy Physics consortium (composed of the University of Melbourne, the University of Sydney and ANSTO) has been investigating the possibility of producing a large area wheel of SI GaAs detectors for the ATLAS detector array. To help assess the extent of Australia's role in this venture a few SI GaAs microstrip detectors are to be manufactured under contract by the CSIRO division of Radiophysics GaAs IC Prototyping Facility. The planned production of the devices is discussed. First, the reasons for producing the detectors here in Australia are examined, then some basic characteristics of the material are considered, and finally details are provided of the design used for the manufacture of the devices. Two sets of detectors will be produced using the standard Glasgow production recipe; SIGaAs and GaN. The Glasgow mask set is being used as a benchmark against which to compare the Australian devices

Donor level of interstitial hydrogen in GaAs

International Nuclear Information System (INIS)

Dobaczewski, L.; Bonde Nielsen, K.; Nylandsted Larsen, A.; Peaker, A.R.

2006-01-01

The first data evidencing the existence of the donor level of the interstitial hydrogen in GaAs are presented. The abundant formation of the (0/+) donor level after in situ low-temperature implantation of hydrogen into the depletion layer of GaAs Schottky diodes has been observed and the activation energy and annealing properties have been determined by Laplace DLTS. The activation energy for electron emission of this donor state is 0.14eV. Above 100K the hydrogen deep donor state is unstable, converting to a more stable form when there are electrons available for the capture process. A slightly perturbed form of the hydrogen donor in its neutral charge state can be recovered by illuminating the sample. This process releases twice as many electrons as the ionisation process of the hydrogen donor state itself. This fact, by analogy with the silicon case, evidences the negative-U behaviour of hydrogen in GaAs

Molecular-beam epitaxy on shallow mesa gratings patterned on GaAs(311)A and (100) substrates

NARCIS (Netherlands)

Gong, Q.; Nötzel, R.; Schönherr, H.-P.; Ploog, K.H.

2002-01-01

We report on the morphology and properties of the surface formed by molecular-beam epitaxy on shallow mesa gratings on patterned GaAs(311)A and GaAs(100). On GaAs(311)A substrates, the corrugated surface formed after GaAs growth on shallow mesa gratings along [011] is composed of monolayer high

Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

International Nuclear Information System (INIS)

Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

2010-01-01

Molecular-Beam Epitaxy growth of multiple In 0.4 Ga 0.6 As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4 Ga 0.6 As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4 Ga 0.6 As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

Levitated Optomechanics for Fundamental Physics

Science.gov (United States)

Rashid, Muddassar; Bateman, James; Vovrosh, Jamie; Hempston, David; Ulbricht, Hendrik

2015-05-01

Optomechanics with levitated nano- and microparticles is believed to form a platform for testing fundamental principles of quantum physics, as well as find applications in sensing. We will report on a new scheme to trap nanoparticles, which is based on a parabolic mirror with a numerical aperture of 1. Combined with achromatic focussing, the setup is a cheap and readily straightforward solution to trapping nanoparticles for further study. Here, we report on the latest progress made in experimentation with levitated nanoparticles; these include the trapping of 100 nm nanodiamonds (with NV-centres) down to 1 mbar as well as the trapping of 50 nm Silica spheres down to 10?4 mbar without any form of feedback cooling. We will also report on the progress to implement feedback stabilisation of the centre of mass motion of the trapped particle using digital electronics. Finally, we argue that such a stabilised particle trap can be the particle source for a nanoparticle matterwave interferometer. We will present our Talbot interferometer scheme, which holds promise to test the quantum superposition principle in the new mass range of 106 amu. EPSRC, John Templeton Foundation.

Electronic structure of GaAs with InAs (001) monolayer

International Nuclear Information System (INIS)

Tit, N.; Peressi, M.

1995-04-01

The effect on the electronic structure of an InAs monomolecular plane inserted in bulk GaAs is investigated theoretically. The (InAs) 1 (GaAs) n (001) strained superlattice is studied via ab-initio self-consistent pseudopotential calculations. Both electrons and holes are localized nearby the inserted InAs monolayer, which therefore acts as a quantum well for all the charge carriers. The small thickness of the inserted InAs slab is responsible of high confinement energies for the charge carriers, and therefore the interband electron-heavy-hole transition energy is close to the energy gap of the bulk GaAs, in agreement with recent experimental data. (author). 18 refs, 4 figs

Guided Acoustic and Optical Waves in Silicon-on-Insulator for Brillouin Scattering and Optomechanics

Science.gov (United States)

2016-08-01

APL PHOTONICS 1, 071301 (2016) Guided acoustic and optical waves in silicon-on- insulator for Brillouin scattering and optomechanics Christopher J...is possible to simultaneously guide optical and acoustic waves in the technologically important silicon on insulator (SOI) material system. Thin...high sound velocity — makes guiding acoustic waves difficult, motivating the use of soft chalcogenide glasses and partial or complete releases (removal

Realizing a Circuit Analog of an Optomechanical System with Longitudinally Coupled Superconducting Resonators

OpenAIRE

Eichler, C.; Petta, J. R.

2017-01-01

We realize a superconducting circuit analog of the generic cavity-optomechanical Hamiltonian by longitudinally coupling two superconducting resonators, which are an order of magnitude different in frequency. We achieve longitudinal coupling by embedding a superconducting quantum interference device (SQUID) into a high frequency resonator, making its resonance frequency depend on the zero point current fluctuations of a nearby low frequency LC-resonator. By employing sideband drive fields we e...

High microwave performance ion-implanted GaAs MESFETs on InP substrates

International Nuclear Information System (INIS)

Wada, M.; Kato, K.

1990-01-01

Ion implantation was employed, for the first time, in fabricating GaAs MESFETs in undoped 2 μm thick GaAs epitaxial layers directly grown on InP substrates by low-pressure MOVPE. The Si-ion-implanted GaAs layer on InP substrates showed excellent electrical characteristics: a mobility of 4300 cm 2 /Vs with a carrier density of 2 x 10 17 cm -3 at room temperature. The MESFET (0.8 μm gate length) exhibited a current-gain cutoff frequency of 25 GHz and a maximum frequency of oscillation of 53 GHz, the highest values yet reported to GaAs MESFETs on InP substrates. These results demonstrate the high potential of ion-implanted MESFETs as electronic devices for high-speed InP-based OEICs. (author)

Nanoscale interfacial engineering to grow Ge on Si as virtual substrates and subsequent integration of GaAs

Energy Technology Data Exchange (ETDEWEB)

Leonhardt, Darin [Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States); Sheng, Josephine; Cederberg, Jeffrey G.; Li Qiming; Carroll, Malcolm S. [Sandia National Laboratories, Albuquerque, NM 87185 (United States); Han, Sang M., E-mail: meister@unm.ed [Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (United States)

2010-08-31

We have demonstrated the scalability of a process previously dubbed as Ge 'touchdown' on Si to substantially reduce threading dislocations below 10{sup 7}/cm{sup 2} in a Ge film grown on a 2 inch-diameter chemically oxidized Si substrate. This study also elucidates the overall mechanism of the touchdown process. The 1.4 nm thick chemical oxide is first formed by immersing Si substrates in a solution of H{sub 2}O{sub 2} and H{sub 2}SO{sub 4}. Subsequent exposure to Ge flux creates 3 to 7 nm-diameter voids in the oxide at a density greater than 10{sup 11}/cm{sup 2}. Comparison of data taken from many previous studies and ours shows an exponential dependence between oxide thickness and inverse temperature of void formation. Additionally, exposure to a Ge or Si atom flux decreases the temperature at which voids begin to form in the oxide. These results strongly suggest that Ge actively participates in the reaction with SiO{sub 2} in the void formation process. Once voids are created in the oxide under a Ge flux, Ge islands selectively nucleate within the void openings on the newly exposed Si. Island nucleation and growth then compete with the void growth reaction. At substrate temperatures between 823 and 1053 K, nanometer size Ge islands that nucleate within the voids continue to grow and coalesce into a continuous film over the remaining oxide. Coalescence of the Ge islands is believed to result in the creation of stacking faults in the Ge film at a density of 5 x 10{sup 7}/cm{sup 2}. Additionally, coalescence results in films of 3 {mu}m thickness having a root-mean-square roughness of 8 to 10 nm. We have found that polishing the films with dilute H{sub 2}O{sub 2} results in roughness values below 0.5 nm. However, stacking faults originating at the Ge-SiO{sub 2} interface and terminating at the Ge surface are polished at a slightly reduced rate, and show up as 1 to 2 nm raised lines on the polished Ge surface. These lines are then transferred into the

Temperature conditions for GaAs nanowire formation by Au-assisted molecular beam epitaxy

International Nuclear Information System (INIS)

Tchernycheva, M; Harmand, J C; Patriarche, G; Travers, L; Cirlin, G E

2006-01-01

Molecular beam epitaxial growth of GaAs nanowires using Au particles as a catalyst was investigated. Prior to the growth during annealing, Au alloyed with Ga coming from the GaAs substrate, and melted. Phase transitions of the resulting particles were observed in situ by reflection high-energy electron diffraction (RHEED). The temperature domain in which GaAs nanowire growth is possible was determined. The lower limit of this domain (320 deg. C) is close to the observed catalyst solidification temperature. Below this temperature, the catalyst is buried by GaAs growth. Above the higher limit (620 deg. C), the catalyst segregates on the surface with no significant nanowire formation. Inside this domain, the influence of growth temperature on the nanowire morphology and crystalline structure was investigated in detail by scanning electron microscopy and transmission electron microscopy. The correlation of the nanowire morphology with the RHEED patterns observed during the growth was established. Wurtzite GaAs was found to be the dominant crystal structure of the wires

Near-field levitated quantum optomechanics with nanodiamonds

Science.gov (United States)

Juan, M. L.; Molina-Terriza, G.; Volz, T.; Romero-Isart, O.

2016-08-01

We theoretically show that the dipole force of an ensemble of quantum emitters embedded in a dielectric nanosphere can be exploited to achieve near-field optical levitation. The key ingredient is that the polarizability from the ensemble of embedded quantum emitters can be larger than the bulk polarizability of the sphere, thereby enabling the use of repulsive optical potentials and consequently the levitation using optical near fields. In levitated cavity quantum optomechanics, this could be used to boost the single-photon coupling by combining larger polarizability to mass ratio, larger field gradients, and smaller cavity volumes while remaining in the resolved sideband regime and at room temperature. A case study is done with a nanodiamond containing a high density of silicon-vacancy color centers that is optically levitated in the evanescent field of a tapered nanofiber and coupled to a high-finesse microsphere cavity.

Elimination of Bimodal Size in InAs/GaAs Quantum Dots for Preparation of 1.3-μm Quantum Dot Lasers.

Science.gov (United States)

Su, Xiang-Bin; Ding, Ying; Ma, Ben; Zhang, Ke-Lu; Chen, Ze-Sheng; Li, Jing-Lun; Cui, Xiao-Ran; Xu, Ying-Qiang; Ni, Hai-Qiao; Niu, Zhi-Chuan

2018-02-21

The device characteristics of semiconductor quantum dot lasers have been improved with progress in active layer structures. Self-assembly formed InAs quantum dots grown on GaAs had been intensively promoted in order to achieve quantum dot lasers with superior device performances. In the process of growing high-density InAs/GaAs quantum dots, bimodal size occurs due to large mismatch and other factors. The bimodal size in the InAs/GaAs quantum dot system is eliminated by the method of high-temperature annealing and optimized the in situ annealing temperature. The annealing temperature is taken as the key optimization parameters, and the optimal annealing temperature of 680 °C was obtained. In this process, quantum dot growth temperature, InAs deposition, and arsenic (As) pressure are optimized to improve quantum dot quality and emission wavelength. A 1.3-μm high-performance F-P quantum dot laser with a threshold current density of 110 A/cm 2 was demonstrated.

1 million-Q optomechanical microdisk resonators for sensing with very large scale integration

Science.gov (United States)

Hermouet, M.; Sansa, M.; Banniard, L.; Fafin, A.; Gely, M.; Allain, P. E.; Santos, E. Gil; Favero, I.; Alava, T.; Jourdan, G.; Hentz, S.

2018-02-01

Cavity optomechanics have become a promising route towards the development of ultrasensitive sensors for a wide range of applications including mass, chemical and biological sensing. In this study, we demonstrate the potential of Very Large Scale Integration (VLSI) with state-of-the-art low-loss performance silicon optomechanical microdisks for sensing applications. We report microdisks exhibiting optical Whispering Gallery Modes (WGM) with 1 million quality factors, yielding high displacement sensitivity and strong coupling between optical WGMs and in-plane mechanical Radial Breathing Modes (RBM). Such high-Q microdisks with mechanical resonance frequencies in the 102 MHz range were fabricated on 200 mm wafers with Variable Shape Electron Beam lithography. Benefiting from ultrasensitive readout, their Brownian motion could be resolved with good Signal-to-Noise ratio at ambient pressure, as well as in liquid, despite high frequency operation and large fluidic damping: the mechanical quality factor reduced from few 103 in air to 10's in liquid, and the mechanical resonance frequency shifted down by a few percent. Proceeding one step further, we performed an all-optical operation of the resonators in air using a pump-probe scheme. Our results show our VLSI process is a viable approach for the next generation of sensors operating in vacuum, gas or liquid phase.

GaAs structures with InAs and As quantum dots produced in a single molecular beam epitaxy process

International Nuclear Information System (INIS)

Nevedomskii, V. N.; Bert, N. A.; Chaldyshev, V. V.; Preobrazhenskii, V. V.; Putyato, M. A.; Semyagin, B. R.

2009-01-01

Epitaxial GaAs layers containing InAs semiconductor quantum dots and As metal quantum dots are grown by molecular beam epitaxy. The InAs quantum dots are formed by the Stranskii-Krastanow mechanism, whereas the As quantum dots are self-assembled in the GaAs layer grown at low temperature with a large As excess. The microstructure of the samples is studied by transmission electron microscopy. It is established that the As metal quantum dots formed in the immediate vicinity of the InAs semiconductor quantum dots are larger in size than the As quantum dots formed far from the InAs quantum dots. This is apparently due to the effect of strain fields of the InAs quantum dots upon the self-assembling of As quantum dots. Another phenomenon apparently associated with local strains around the InAs quantum dots is the formation of V-like defects (stacking faults) during the overgrowth of the InAs quantum dots with the GaAs layer by low-temperature molecular beam epitaxy. Such defects have a profound effect on the self-assembling of As quantum dots. Specifically, on high-temperature annealing needed for the formation of large-sized As quantum dots by Ostwald ripening, the V-like defects bring about the dissolution of the As quantum dots in the vicinity of the defects. In this case, excess arsenic most probably diffuses towards the open surface of the sample via the channels of accelerated diffusion in the planes of stacking faults.

Testing a GaAs cathode in SRF gun

International Nuclear Information System (INIS)

Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

2011-01-01

RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10 -12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to ∼10 -9 Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high accelerating

Investigations on liquid phase electroepitaxial growth kinetics of GaAs

International Nuclear Information System (INIS)

Mouleeswaran, D.; Dhanasekaran, R.

2004-01-01

This paper presents a model based on solving a two-dimensional diffusion equation incorporating the electromigration effect by numerical simulation method corresponding to liquid phase electroepitaxial (LPEE) growth of GaAs, whose growth is limited by diffusion and electro migration of solute species. Using the numerical simulation method, the concentration profiles of As in Ga rich solution during the electroepitaxial growth of GaAs have been constructed in front of the growing crystal interface. Using the concentration gradient at the interface, the growth rate and thickness of the epitaxial layer of GaAs have been determined for different experimental growth conditions. The proposed model is based on the assumption that there is no convection in the solution. The results are discussed in detail

Tailoring broadband light trapping of GaAs and Si substrates by self-organised nanopatterning

Energy Technology Data Exchange (ETDEWEB)

Martella, C.; Chiappe, D.; Mennucci, C.; Buatier de Mongeot, F. [Dipartimento di Fisica, Università di Genova, via Dodecaneso 33, I-16146 Genova (Italy)

2014-05-21

We report on the formation of high aspect ratio anisotropic nanopatterns on crystalline GaAs (100) and Si (100) substrates exploiting defocused Ion Beam Sputtering assisted by a sacrificial self-organised Au stencil mask. The tailored optical properties of the substrates are characterised in terms of total reflectivity and haze by means of integrating sphere measurements as a function of the morphological modification at increasing ion fluence. Refractive index grading from sub-wavelength surface features induces polarisation dependent anti-reflection behaviour in the visible-near infrared (VIS-NIR) range, while light scattering at off-specular angles from larger structures leads to very high values of the haze functions in reflection. The results, obtained for an important class of technologically relevant materials, are appealing in view of photovoltaic and photonic applications aiming at photon harvesting in ultrathin crystalline solar cells.

Effect of semiconductor GaAs laser irradiation on pain perception in mice

Energy Technology Data Exchange (ETDEWEB)

Zarkovic, N.; Manev, H.; Pericic, D.; Skala, K.; Jurin, M.; Persin, A.; Kubovic, M.

1989-01-01

The influence of subacute exposure (11 exposures within 16 days) of mice to the low power (GaAs) semiconductive laser-stimulated irradiation on pain perception was investigated. The pain perception was determined by the latency of foot-licking or jumping from the surface of a 53 degrees C hot plate. Repeated hot-plate testing resulted in shortening of latencies in both sham- and laser-irradiated mice. Laser treatment (wavelength, 905 nm; frequency, 256 Hz; irradiation time, 50 sec; pulse duration, 100 nsec; distance, 3 cm; peak irradiance, 50 W/cm2 in irradiated area; and total exposure, 0.41 mJ/cm2) induced further shortening of latencies, suggesting its stimulatory influence on pain perception. Administration of morphine (20 mg/kg) prolonged the latency of response to the hot plate in both sham- and laser-irradiated mice. This prolongation tended to be lesser in laser-irradiated animals. Further investigations are required to elucidate the mechanism of the observed effect of laser.

The tomography inside of a Fourier Optics course: some opto-mechanical illustrative arrays

International Nuclear Information System (INIS)

Rodriguez Z, G.; Rodriguez V, R.; Luna C, A.

1999-01-01

The introduction of tomography as an advanced topic to be included in a Fourier optics course at graduated level is proposed. It is shown a possible presentation sequence which features the use of typical Fourier optics techniques, as well as some well known opto-mechanical devices as examples. Finally, a simplified apparatus which illustrates the central Fourier theorem as an experimental project on Fourier optics is described. Corresponding experimental results are also shown. (Author)

Free-space wavelength-multiplexed optical scanner.

Science.gov (United States)

Yaqoob, Z; Rizvi, A A; Riza, N A

2001-12-10

A wavelength-multiplexed optical scanning scheme is proposed for deflecting a free-space optical beam by selection of the wavelength of the light incident on a wavelength-dispersive optical element. With fast tunable lasers or optical filters, this scanner features microsecond domain scan setting speeds and large- diameter apertures of several centimeters or more for subdegree angular scans. Analysis performed indicates an optimum scan range for a given diffraction order and grating period. Limitations include beam-spreading effects based on the varying scanner aperture sizes and the instantaneous information bandwidth of the data-carrying laser beam.

Reflectance-anisotropy study of the dynamics of molecular beam epitaxy growth of GaAs and InGaAs on GaAs(001)

Energy Technology Data Exchange (ETDEWEB)

Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Balderas-Navarro, R.E. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Facultad de Ciencias, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico)

2008-07-01

Reflectance-Anisotropy (RA) observations during the Molecular Beam Epitaxy (MBE) growth of zincblende semiconductors films were carried out using the E{sub 1} optical transition as a probe. We follow the kinetics of the deposition of GaAs and In{sub 0.3}Ga{sub 0.7}As on GaAs(001) at growth rates of 0.2 and 0.25 ML/s, respectively. During growth we used a constant As{sub 4} or As{sub 2} flux pressure of 5 x 10{sup -6} Torr. Clear RA-oscillations were observed during growth with a period that nearly coincides with the growth period for a Ga-As bilayer. RHEED was used as an auxiliary technique in order to obtain a correlation between RHEED and RA oscillations. On the basis of our results, we argue that RAS oscillations are mainly associated to periodic changes in surface atomic structure. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Reflectance-anisotropy study of the dynamics of molecular beam epitaxy growth of GaAs and InGaAs on GaAs(001)

International Nuclear Information System (INIS)

Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F.; Balderas-Navarro, R.E.

2008-01-01

Reflectance-Anisotropy (RA) observations during the Molecular Beam Epitaxy (MBE) growth of zincblende semiconductors films were carried out using the E 1 optical transition as a probe. We follow the kinetics of the deposition of GaAs and In 0.3 Ga 0.7 As on GaAs(001) at growth rates of 0.2 and 0.25 ML/s, respectively. During growth we used a constant As 4 or As 2 flux pressure of 5 x 10 -6 Torr. Clear RA-oscillations were observed during growth with a period that nearly coincides with the growth period for a Ga-As bilayer. RHEED was used as an auxiliary technique in order to obtain a correlation between RHEED and RA oscillations. On the basis of our results, we argue that RAS oscillations are mainly associated to periodic changes in surface atomic structure. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Polarimetric Detection of Enantioselective Adsorption by Chiral Au Nanoparticles – Effects of Temperature, Wavelength and Size

Directory of Open Access Journals (Sweden)

Nisha Shukla

2015-01-01

Full Text Available R- and S-propylene oxide (PO have been shown to interact enantiospecifically with the chiral surfaces of Au nanopar‐ ticles (NPs modified with D- or L-cysteine (cys. This enantiospecific interaction has been detected using optical polarimetry measurements made on solutions of the D- or L-cys modified Au (cys/Au NPs during addition of racemic PO. The selective adsorption of one enantiomer of the PO onto the cys/Au NP surfaces results in a net rotation of light during addition of the racemic PO to the solution. In order to optimize the conditions used for making these measurements and to quantify enantiospecific adsorption onto chiral NPs, this work has measured the effect of temperature, wavelength and Au NP size on optical rotation by solutions containing D- or L-cys/Au NPs and racemic PO. Increasing temperature, decreasing wave‐ length and decreasing NP size result in larger optical rotations.

Effects of surface passivation on twin-free GaAs nanosheets.

Science.gov (United States)

Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

2015-02-24

Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation.

Electric field effect of GaAs monolayer from first principles

Directory of Open Access Journals (Sweden)

Jiongyao Wu

2017-03-01

Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

Substrate and Mg doping effects in GaAs nanowires

Directory of Open Access Journals (Sweden)

Perumal Kannappan

2017-10-01

Full Text Available Mg doping of GaAs nanowires has been established as a viable alternative to Be doping in order to achieve p-type electrical conductivity. Although reports on the optical properties are available, few reports exist about the physical properties of intermediate-to-high Mg doping in GaAs nanowires grown by molecular beam epitaxy (MBE on GaAs(111B and Si(111 substrates. In this work, we address this topic and present further understanding on the fundamental aspects. As the Mg doping was increased, structural and optical investigations revealed: i a lower influence of the polytypic nature of the GaAs nanowires on their electronic structure; ii a considerable reduction of the density of vertical nanowires, which is almost null for growth on Si(111; iii the occurrence of a higher WZ phase fraction, in particular for growth on Si(111; iv an increase of the activation energy to release the less bound carrier in the radiative state from nanowires grown on GaAs(111B; and v a higher influence of defects on the activation of nonradiative de-excitation channels in the case of nanowires only grown on Si(111. Back-gate field effect transistors were fabricated with individual nanowires and the p-type electrical conductivity was measured with free hole concentration ranging from 2.7 × 1016 cm−3 to 1.4 × 1017 cm−3. The estimated electrical mobility was in the range ≈0.3–39 cm2/Vs and the dominant scattering mechanism is ascribed to the WZ/ZB interfaces. Electrical and optical measurements showed a lower influence of the polytypic structure of the nanowires on their electronic structure. The involvement of Mg in one of the radiative transitions observed for growth on the Si(111 substrate is suggested.

Cryogenic scintillation properties of n-type GaAs for the direct detection of MeV/c2 dark matter

Science.gov (United States)

Derenzo, S.; Bourret, E.; Hanrahan, S.; Bizarri, G.

2018-03-01

This paper is the first report of n-type GaAs as a cryogenic scintillation radiation detector for the detection of electron recoils from interacting dark matter (DM) particles in the poorly explored MeV/c2 mass range. Seven GaAs samples from two commercial suppliers and with different silicon and boron concentrations were studied for their low temperature optical and scintillation properties. All samples are n-type even at low temperatures and exhibit emission between silicon donors and boron acceptors that peaks at 1.33 eV (930 nm). The lowest excitation band peaks at 1.44 eV (860 nm), and the overlap between the emission and excitation bands is small. The X-ray excited luminosities range from 7 to 43 photons/keV. Thermally stimulated luminescence measurements show that n-type GaAs does not accumulate metastable radiative states that could cause afterglow. Further development and use with cryogenic photodetectors promises a remarkable combination of large target size, ultra-low backgrounds, and a sensitivity to electron recoils of a few eV that would be produced by DM particles as light as a few MeV/c2.

Spectroscopy of GaAs quantum wells

International Nuclear Information System (INIS)

West, L.C.

1985-07-01

A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs

Spectroscopy of GaAs quantum wells

Energy Technology Data Exchange (ETDEWEB)

West, L.C.

1985-07-01

A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.

GaAs optoelectronic neuron arrays

Science.gov (United States)

Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

1993-01-01

A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

Single-dot Spectroscopy of GaAs Quantum Dots Fabricated by Filling of Self-assembled Nanoholes

Directory of Open Access Journals (Sweden)

Heyn Ch

2010-01-01

Full Text Available Abstract We study the optical emission of single GaAs quantum dots (QDs. The QDs are fabricated by filling of nanoholes in AlGaAs and AlAs which are generated in a self-assembled fashion by local droplet etching with Al droplets. Using suitable process parameters, we create either uniform QDs in partially filled deep holes or QDs with very broad size distribution in completely filled shallow holes. Micro photoluminescence measurements of single QDs of both types establish sharp excitonic peaks. We measure a fine-structure splitting in the range of 22–40μeV and no dependence on QD size. Furthermore, we find a decrease in exciton–biexciton splitting with increasing QD size.

Fabrication and optical properties of multishell InAs quantum dots on GaAs nanowires

Energy Technology Data Exchange (ETDEWEB)

Yan, Xin; Zhang, Xia, E-mail: xzhang@bupt.edu.cn; Li, Junshuai; Cui, Jiangong; Ren, Xiaomin [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

2015-02-07

Hybrid nanostructures combining nanowires with quantum dots promote the development of nanoelectronic and nanophotonic devices with integrated functionalities. In this work, we present a complex nanostructure with multishell quantum dots grown on nanowires. 1–4 shells of Stranski-Krastanov InAs quantum dots are grown on the sidewalls of GaAs nanowires by metal organic chemical vapor deposition. Different dot shells are separated by 8 nm GaAs spacer shells. With increasing the number of shells, the quantum dots become sparser and tend to align in one array, which is caused by the shrinkage of facets on which dots prefer to grow as well as the strain fields produced by the lower set of dots which influences the migration of In adatoms. The size of quantum dots increases with the increase of shell number due to enhanced strain fields coupling. The spectra of multishell dots exhibit multiwavelength emission, and each peak corresponds to a dot shell. This hybrid structure may serve as a promising element in nanowire intermediate band solar cells, infrared nanolasers, and photodetectors.

Torsional Optomechanics of a Levitated Nonspherical Nanoparticle

Science.gov (United States)

Hoang, Thai M.; Ma, Yue; Ahn, Jonghoon; Bang, Jaehoon; Robicheaux, F.; Yin, Zhang-Qi; Li, Tongcang

2016-09-01

An optically levitated nanoparticle in vacuum is a paradigm optomechanical system for sensing and studying macroscopic quantum mechanics. While its center-of-mass motion has been investigated intensively, its torsional vibration has only been studied theoretically in limited cases. Here we report the first experimental observation of the torsional vibration of an optically levitated nonspherical nanoparticle in vacuum. We achieve this by utilizing the coupling between the spin angular momentum of photons and the torsional vibration of a nonspherical nanoparticle whose polarizability is a tensor. The torsional vibration frequency can be 1 order of magnitude higher than its center-of-mass motion frequency, which is promising for ground state cooling. We propose a simple yet novel scheme to achieve ground state cooling of its torsional vibration with a linearly polarized Gaussian cavity mode. A levitated nonspherical nanoparticle in vacuum will also be an ultrasensitive nanoscale torsion balance with a torque detection sensitivity on the order of 10-29 N m /√{Hz } under realistic conditions.

Enhancement of conductance of GaAs sub-microwires under external stimuli

Science.gov (United States)

Qu, Xianlin; Deng, Qingsong; Zheng, Kun

2018-03-01

Semiconductors with one dimension on the micro-nanometer scale have many unique physical properties that are remarkably different from those of their bulk counterparts. Moreover, changes in the external field will further modulate the properties of the semiconductor micro-nanomaterials. In this study, we used focused ion beam technology to prepare freestanding ⟨111⟩-oriented GaAs sub-microwires from a GaAs substrate. The effects of laser irradiation and bending or buckling deformation induced by compression on the electrical transport properties of an individual GaAs sub-microwire were studied. The experimental results indicate that both laser irradiation and bending deformation can enhance their electrical transport properties, the laser irradiation resulted in a conductance enhancement of ˜30% compared to the result with no irradiation, and in addition, bending deformation changed the conductance by as much as ˜180% when the average strain was approximately 1%. The corresponding mechanisms are also discussed. This study provides beneficial insight into the fabrication of electronic and optoelectronic devices based on GaAs micro/nano-wires.

Response of GaAs charge storage devices to transient ionizing radiation

Science.gov (United States)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

International Nuclear Information System (INIS)

Chen Liang; Qian Yun-Sheng; Zhang Yi-Jun; Chang Ben-Kang

2012-01-01

Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage (SPV) curve before activation and the spectral response curve (SRC) after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability (SEP) can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Metallization systems for stable ohmic contacts to GaAs

International Nuclear Information System (INIS)

Tandon, J.L.; Douglas, K.D.; Vendura, G.; Kolawa, E.; So, F.C.T.; Nicolet, M.A.

1986-01-01

A metallization scheme to form reproducible and stable ohmic contacts to GaAs is described. The approach is based on the configuration: GaAs/X/Y/Z; where X is a thin metal film (e.g. Pt, Ti, Pd, Ru), Y is an electrically conducting diffusion barrier layer (TiN, W or W/sub 0.7/N/sub 0.3/), and Z is a thick metal layer (e.g. Ag) typically required for bonding or soldering purposes. The value and reproducibility of the contact resistance in these metallization systems results from the uniform steady-state solid-phase reaction of the metal X with GaAs. The stability of the contacts is achieved by the diffusion barrier layer Y, which not only confines the reaction of X with GaAs, but also prevents the top metal layer Z from interfering with this reaction. Applications of such contacts in fabricating stable solar cells are also discussed

Fully reconfigurable 2x2 optical cross-connect using tunable wavelength switching modules

DEFF Research Database (Denmark)

Liu, Fenghai; Zheng, Xueyan; Pedersen, Rune Johan Skullerud

2001-01-01

A modular tunable wavelength switching module is proposed and used to construct 2x2 fully reconfigurable optical cross-connects. Large size optical switch is avoided in the OXC and it is easy to upgrade to more wavelength channels.......A modular tunable wavelength switching module is proposed and used to construct 2x2 fully reconfigurable optical cross-connects. Large size optical switch is avoided in the OXC and it is easy to upgrade to more wavelength channels....

Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

Science.gov (United States)

Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

1987-01-01

GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

Growth and characterization of InAs columnar quantum dots on GaAs substrate

International Nuclear Information System (INIS)

Li, L. H.; Patriarche, G.; Rossetti, M.; Fiore, A.

2007-01-01

The growth of InAs columnar quantum dots (CQDs) on GaAs substrates by molecular beam epitaxy was investigated. The CQDs were formed by depositing a 1.8 monolayer (ML) InAs seed dot layer and a short period GaAs/InAs superlattice (SL). It was found that the growth of the CQDs is very sensitive to growth interruption (GI) and growth temperature. Both longer GI and higher growth temperature impact the size dispersion of the CQDs, which causes the broadening of photoluminescence (PL) spectrum and the presence of the additional PL peak tails. By properly choosing the GI and the growth temperature, CQDs including GaAs (3 ML)/InAs (0.62 ML) SL with period number up to 35 without plastic relaxation were grown. The corresponding equivalent thickness of the SL is 41 nm which is two times higher than the theoretical critical thickness of the strained InGaAs layer with the same average In composition of 16%. The increase of the critical thickness is partially associated with the formation of the CQDs. Based on a five-stack CQD active region, laser diodes emitting around 1120 nm at room temperature were demonstrated, indicating a high material quality. CQDs with nearly isotropic cross section (20 nmx20 nm dimensions) were formed by depositing a 16-period GaAs (3 ML)/InAs (0.62 ML) SL on an InAs seed dot layer, indicating the feasibility of artificial shape engineering of QDs. Such a structure is expected to be very promising for polarization insensitive device applications, such as semiconductor optical amplifiers

Transformational III-V Electronics

KAUST Repository

Nour, Maha A.

2014-04-01

Flexible electronics using III-V materials for nano-electronics with high electron mobility and optoelectronics with direct band gap are attractive for many applications. This thesis describes a complementary metal oxide semiconductor (CMOS) compatible process for transforming traditional III-V materials based electronics into flexible one. The thesis reports releasing 200 nm of Gallium Arsenide (GaAs) from 200 nm GaAs / 300 nm Aluminum Arsenide (AlAs) stack on GaAs substrate using diluted hydrofluoric acid (HF). This process enables releasing a single top layer compared to peeling off all layers with small sizes at the same time. This is done utilizing a network of release holes that contributes to the better transparency (45 % at 724 nm wavelengths) observed. Fabrication of metal oxide semiconductor capacitor (MOSCAPs) on GaAs is followed by releasing it to have devices on flexible 200 nm GaAs. Similarly, flexible GaSb and InP fabrication process is also reported to transform traditional electronics into large-area flexible electronics.

Transient radiation effects in GaAs semiconductor devices

International Nuclear Information System (INIS)

Chang, J.Y.; Stauber, M.; Ezzeddine, A.; Howard, J.W.; Constantine, A.G.; Becker, M.; Block, R.C.

1988-01-01

This paper describes an ongoing program to identify the response of GaAs devices to intense pulses of ionizing radiation. The program consists of experimental measurements at the Rensselaer Polytechnic Institute's RPI electron linear accelerator (Linac) on generic GaAs devices built by Grumman Tachonics Corporation and the analysis of these results through computer simulation with the circuit model code SPICE (including radiation effects incorporated in the variations TRISPICE and TRIGSPICE and the device model code PISCES IIB). The objective of this program is the observation of the basic response phenomena and the development of accurate simulation tools so that results of Linac irradiations tests can be understood and predicted

Nonequilibrium Quantum Phase Transition in a Hybrid Atom-Optomechanical System

Science.gov (United States)

Mann, Niklas; Bakhtiari, M. Reza; Pelster, Axel; Thorwart, Michael

2018-02-01

We consider a hybrid quantum many-body system formed by a vibrational mode of a nanomembrane, which interacts optomechanically with light in a cavity, and an ultracold atom gas in the optical lattice of the out-coupled light. The adiabatic elimination of the light field yields an effective Hamiltonian which reveals a competition between the force localizing the atoms and the membrane displacement. At a critical atom-membrane interaction, we find a nonequilibrium quantum phase transition from a localized symmetric state of the atom cloud to a shifted symmetry-broken state, the energy of the lowest collective excitation vanishes, and a strong atom-membrane entanglement arises. The effect occurs when the atoms and the membrane are nonresonantly coupled.

Self-Assembled Monolayers of CdSe Nanocrystals on Doped GaAs Substrates

DEFF Research Database (Denmark)

Marx, E.; Ginger, D.S.; Walzer, Karsten

2002-01-01

This letter reports the self-assembly and analysis of CdSe nanocrystal monolayers on both p- and a-doped GaAs substrates. The self-assembly was performed using a 1,6-hexanedithiol self-assembled monolayer (SAM) to link CdSe nanocrystals to GaAs substrates. Attenuated total reflection Fourier tran...

Superconducting NbN single-photon detectors on GaAs with an AlN buffer layer

Energy Technology Data Exchange (ETDEWEB)

Schmidt, Ekkehart; Merker, Michael; Ilin, Konstantin; Siegel, Michael [Institut fuer Mikro- und Nanoelektronische Systeme (IMS), Karlsruher Institut fuer Technologie, Hertzstrasse 16, 76187 Karlsruhe (Germany)

2015-07-01

GaAs is the material of choice for photonic integrated circuits. It allows the monolithic integration of single-photon sources like quantum dots, waveguide based optical circuits and detectors like superconducting nanowire single-photon detectors (SNSPDs) onto one chip. The growth of high quality NbN films on GaAs is challenging, due to natural occurring surface oxides and the large lattice mismatch of about 27%. In this work, we try to overcome these problems by the introduction of a 10 nm AlN buffer layer. Due to the buffer layer, the critical temperature of 6 nm thick NbN films was increased by about 1.5 K. Furthermore, the critical current density at 4.2 K of NbN flim deposited onto GaAs with AlN buffer is 50% higher than of NbN film deposited directly onto GaAs substrate. We successfully fabricated NbN SNSPDs on GaAs with a AlN buffer layer. SNSPDs were patterned using electron-beam lithography and reactive-ion etching techniques. Results on the study of detection efficiency and jitter of a NbN SNSPD on GaAs, with and without AlN buffer layer will be presented and discussed.

Ka-band IQ vector modulator employing GaAs HBTs

International Nuclear Information System (INIS)

Cao Yuxiong; Wu Danyu; Chen Gaopeng; Jin Zhi; Liu Xinyu

2011-01-01

The importance of high-performance, low-cost and millimeter-wave transmitters for digital communications and radar applications is increasing. The design and performance of a Ka-band balanced in-phase and quadrature-phase (I-Q) type vector modulator, using GaAs heterojunction bipolar transistors (HBTs) as switching elements, are presented. The balanced technique is used to remove the parasitics of the HBTs to result in near perfect constellations. Measurements of the monolithic microwave integrated circuit (MMIC) chip with a size of 1.89 x 2.26 mm 2 demonstrate an amplitude error below 1.5 dB and the phase error within 3 0 between 26 and 40 GHz except for a singular point at 35.6 GHz. The results show that the technique is suitable for millimeter-wave digital communications. (semiconductor integrated circuits)

Mass and energy dispersive recoil spectrometry of GaAs structures

International Nuclear Information System (INIS)

Hult, M.

1994-01-01

Mass and energy dispersive Recoil Spectrometry (RS) using heavy ions at energies of about 0.2Α-0.8Α MeV has attracted much interest recently due to its potential for separately and unambiguously generating information on isotopic depth distributions. The principal advantages of mass and energy dispersive RS are that both light and heavy elements can be separately studied simultaneously and problems caused by chemical matrix effects are avoided since the technique is based on high energy nucleus-nucleus scattering. In order to elucidate reactions taking place in various GaAs structures, Time of flight-Energy (ToF-E) RS was developed to allow Ga and As to be studied separately down to depths of about 500-800 nm with a depth resolution of about 16 nm at the surface. This was shown in a study of an Al x Ga 1-x As quantum-well structure. The benefits of using ToF-E RS on GaAs structures were further demonstrated in studies of Co/GaAs and CoSi 2 /GaAs reactions, as well as in a study of the composition of MOCVD grown Al x Ga 1-x As. Most recoil measurements employed 127 I at energies of about 50-90 MeV as projectiles. The recoil detector telescope consisted of a silicon energy detector and two carbon foil time pick-off detectors separated by a variable flight length of 213.5-961 mm. The reactions taking place between various thin films and GaAs were also studied using complementary techniques such as XRD, XPS and SEM. Co was found to react extensively with GaAs, already at about 300 degrees C, making it unsuitable as a contact material. Thin films of Co and Si were found to react extensively with each other and to form CoSi 2 at 500 degrees C and above. CoSi 2 , a low resistivity silicide, turned out to be stable on GaAs, at least up to 700 degrees C. Considerable grain growth could cause problems, however, in the use of CoSi 2 -contacts. 112 refs, figs, tabs

Modified energetics and growth kinetics on H-terminated GaAs (110)

International Nuclear Information System (INIS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

2013-01-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As 4 , has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å 2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As 4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed

Modified energetics and growth kinetics on H-terminated GaAs (110)

Energy Technology Data Exchange (ETDEWEB)

Galiana, B. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Departamento de Física, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Madrid (Spain); Benedicto, M.; Díez-Merino, L.; Tejedor, P. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Lorbek, S.; Hlawacek, G.; Teichert, C. [Institut für Physik, Montanuniversität Leoben, Franz Josef St., 18A-8700 Leoben (Austria)

2013-10-28

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Surface segregation and the Al problem in GaAs quantum wells

Science.gov (United States)

Chung, Yoon Jang; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

2018-03-01

Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped AlxGa1 -xAs /GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the AlxGa1 -xAs barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the AlxGa1 -xAs barrier beneath the QW is increased, which we attribute to the surface segregation of oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking.

Modeling of altered layer formation during reactive ion etching of GaAs

Energy Technology Data Exchange (ETDEWEB)

Mutzke, A. [Max-Planck-Institute of Plasmaphysics, EURATOM Association, D-17491 Greifswald (Germany); Rai, A., E-mail: Abha.Rai@ipp.mpg.de [Max-Planck-Institute of Plasmaphysics, EURATOM Association, D-17491 Greifswald (Germany); Schneider, R.; Angelin, E.J.; Hippler, R. [Institute of Physics, Ernst-Moritz-Arndt-University Greifswald, Felix-Hausdorff-Str.6, D-17489 Greifswald (Germany)

2012-12-15

Highlights: Black-Right-Pointing-Pointer Experimental result showing the preferential sputtering of GaAs (150 keV Ar{sup +} and thermal O on GaAs) during reactive ion beam etching (RIBE) has been reported. Black-Right-Pointing-Pointer A model based on binary collisions (SDTrimSP) is presented to simulate RIBE. Black-Right-Pointing-Pointer The model is used to explain the reported experimental data and also the results by Grigonis and co-workers [1]. - Abstract: The binary collision based SDTrimSP model has been used to simulate the reactive ion beam etching (RIBE) of GaAs in the presence of energetic Ar ions and thermal O atoms. It includes the collisional effects, diffusive processes and chemical reactions taking place in the system. The model parameters are fitted using the experimental observations of Grigonis and co-workers [1] and validated with the experimental results obtained during the GaAs ion etching presented in this paper. A detailed analysis is presented to understand the effect of the diffusive processes and the role of O during RIBE of GaAs. It is shown how the presence of damage caused by the energetic Ar coupled with the presence of thermal O opens up chemical reaction channels which eventually leads to the preferential sputtering of Ga observed at the ion etching facility at University of Greifswald.

Dielectric micro-resonator-based opto-mechanical systems for sensing applications

Science.gov (United States)

Ali, Amir Roushdy

In recent years, whispering gallery mode (WGM), or morphology dependent optical resonances (MDR) of dielectric micro-resonators have attracted interest with proposed applications in a wide range of areas due to the high optical quality factors, Q, they can exhibit (reaching ~ 10. 9 for silica spheres). Micro-resonator WGMs have been used in applications that include those in spectroscopy, micro-cavity laser technology, optical communications (switching, filtering and multiplexing), sensors technologies and even chemical and biological sensing. The WGM of these dielectric micro-resonators are highly sensitive to morphological changes (such as the size, shape, or refractive index) of the resonance cavity and hence, can be tuned by causing a minute change in the physical condition of the surrounding. In this dissertation, we have been creating opto-mechanical systems, which at their most basic, are extraordinarily sensitive sensors. One of the ultimate goals of this dissertation is to develop sensors capable of detecting the extremely small electric field changes. To improve the performance of the sensors, we couple a polymer cantilever beam to a dielectric micro-resonator. The eventual use of such ultra sensitive electric filed sensors could include neural-machine interfaces for advanced prosthetics devices. The work presented here includes a basic analysis and experimental investigations of the electric field sensitivity and range of micro-resonators of several different materials and geometries followed by the electric field sensor design, testing, and characterization. Also, the effects of angular velocity on the WGM shifts of spherical micro-resonators are also investigated. The elastic deformation that is induced on a spinning resonator due to the centrifugal force may lead to a sufficient shift in the optical resonances and therefore interfering with its desirable operational sensor design. Furthermore, this principle could be used for the development of

Strain in GaAs / InAs core-shell nanowire heterostructures grown on GaAs

Energy Technology Data Exchange (ETDEWEB)

Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Rieger, Torsten; Lepsa, Mihail Ion [Peter Gruenberg Institut 9, Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany)

2012-07-01

The growth of semiconductor nanowires (NWs) has attracted significant interest in recent years due to the possible fabrication of novel semiconductor devices for future electronic and opto-electronic applications. Compared to planar heterostructures, the nanowire approach offers an advantage regarding the possibility to form heterostructures between highly lattice mismatched systems, because the free surface of the nanowires allows to relieve the strain more efficiently. One particular way to form heterostructures in the NW geometry, is the fabrication of core-shell devices, in which a NW core is surrounded by a shell of different material. The understanding of the mutual strain between core and shell, as well as the relaxation behavior of the system are crucial for the fabrication of functional devices. In this contribution we report on first X-ray diffraction measurements of GaAs-core/InAs-shell nanowires grown on GaAs(111) by molecular beam epitaxy. Using symmetric- and grazing-incidence X-ray diffraction, the relaxation state of the InAs shell as well as the strain in the GaAs core are measured as function of the InAs shell thickness, showing a gradual relaxation behavior of the shell.

Radiation-pressure-mediated control of an optomechanical cavity

Science.gov (United States)

Cripe, Jonathan; Aggarwal, Nancy; Singh, Robinjeet; Lanza, Robert; Libson, Adam; Yap, Min Jet; Cole, Garrett D.; McClelland, David E.; Mavalvala, Nergis; Corbitt, Thomas

2018-01-01

We describe and demonstrate a method to control a detuned movable-mirror Fabry-Pérot cavity using radiation pressure in the presence of a strong optical spring. At frequencies below the optical spring resonance, self-locking of the cavity is achieved intrinsically by the optomechanical (OM) interaction between the cavity field and the movable end mirror. The OM interaction results in a high rigidity and reduced susceptibility of the mirror to external forces. However, due to a finite delay time in the cavity, this enhanced rigidity is accompanied by an antidamping force, which destabilizes the cavity. The cavity is stabilized by applying external feedback in a frequency band around the optical spring resonance. The error signal is sensed in the amplitude quadrature of the transmitted beam with a photodetector. An amplitude modulator in the input path to the cavity modulates the light intensity to provide the stabilizing radiation pressure force.

Testing Quantum Gravity Induced Nonlocality via Optomechanical Quantum Oscillators.

Science.gov (United States)

Belenchia, Alessio; Benincasa, Dionigi M T; Liberati, Stefano; Marin, Francesco; Marino, Francesco; Ortolan, Antonello

2016-04-22

Several quantum gravity scenarios lead to physics below the Planck scale characterized by nonlocal, Lorentz invariant equations of motion. We show that such nonlocal effective field theories lead to a modified Schrödinger evolution in the nonrelativistic limit. In particular, the nonlocal evolution of optomechanical quantum oscillators is characterized by a spontaneous periodic squeezing that cannot be generated by environmental effects. We discuss constraints on the nonlocality obtained by past experiments, and show how future experiments (already under construction) will either see such effects or otherwise cast severe bounds on the nonlocality scale (well beyond the current limits set by the Large Hadron Collider). This paves the way for table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology.

The opto-mechanical design process: from vision to reality

Science.gov (United States)

Kvamme, E. Todd; Stubbs, David M.; Jacoby, Michael S.

2017-08-01

The design process for an opto-mechanical sub-system is discussed from requirements development through test. The process begins with a proper mission understanding and the development of requirements for the system. Preliminary design activities are then discussed with iterative analysis and design work being shared between the design, thermal, and structural engineering personnel. Readiness for preliminary review and the path to a final design review are considered. The value of prototyping and risk mitigation testing is examined with a focus on when it makes sense to execute a prototype test program. System level margin is discussed in general terms, and the practice of trading margin in one area of performance to meet another area is reviewed. Requirements verification and validation is briefly considered. Testing and its relationship to requirements verification concludes the design process.

Structural and electronic properties of isovalent boron atoms in GaAs

Science.gov (United States)

Krammel, C. M.; Nattermann, L.; Sterzer, E.; Volz, K.; Koenraad, P. M.

2018-04-01

Boron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of BxGa1-xAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.

Spin transport anisotropy in (110)GaAs

Energy Technology Data Exchange (ETDEWEB)

Odilon, D.D.C. Jr.; Rudolph, Joerg; Hey, Rudolf; Santos, Paulo V. [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany); Iikawa, Fernando [Universidade Estadual de Campinas, IFGW, Campinas SP (Brazil)

2007-07-01

Mobile piezoelectric potentials are used to coherently transport electron spins in GaAs(110) quantum wells (QW) over distances exceeding 60{mu}m. We demonstrate that the dynamics of mobile spins under external magnetic fields depends on the direction of motion in the QW plane. The weak piezoelectric fields impart a non-vanishing average velocity to the carriers, allowing for the direct observation of the carrier momentum dependence of the spin polarization dynamics. While transport along [001] direction presents high in-plane spin relaxation rates, transport along [ anti 110] shows a much weaker external field dependence due to the non-vanishing internal magnetic field. We show that the anisotropy is an intrinsic property of the underling GaAs matrix, associated with the bulk inversion asymmetry contribution to the LS-coupling.

Effects produced in GaAs by MeV ion bombardment

International Nuclear Information System (INIS)

Wie, C.R.

1985-01-01

The first part of this thesis presents work performed on the ionizing energy beam induced adhesion enhancement of thin (approx.500 A) Au films on GaAs substrates. The ionizing beam, employed in the present thesis, is the MeV ions (i.e., 16 O, 19 F, and 35 Cl), with energies between 1 and 20 MeV. Using the Scratch test for adhesion measurement, and ESCA for chemical analysis of the film substrate interface, the native oxide layer at the interface is shown to play an important role in the adhesion enhancement by the ionizing radiation. A model is discussed that explains the experimental data on the dependence of adhesion enhancement on the energy which was deposited into electronic processes at the interface. The second part of the thesis presents research results on the radiation damage in GaAs crystals produced by MeV ions. Lattice parameter dilatation in the surface layers of the GaAs crystals becomes saturated after a high dose bombardment at room temperature. The strain produced by nuclear collisions is shown to relax partially due to electronic excitation (with a functional dependence on the nuclear and electronic stopping power of bombarding ions. Data on the GaAs and GaP crystals suggest that low temperature recovery stage defects produce major crystal distortion

Extended wavelength InGaAs on GaAs using InAlAs buffer for back-side-illuminated short-wave infrared detectors

International Nuclear Information System (INIS)

Zimmermann, Lars; John, Joachim; Degroote, Stefan; Borghs, Gustaaf; Hoof, Chris van; Nemeth, Stefan

2003-01-01

We conducted an experimental study of back-side-illuminated InGaAs photodiodes grown on GaAs and sensitive in the short-wave infrared up to 2.4 μm. Standard metamorphic InGaAs or IR-transparent InAlAs buffers were grown by molecular-beam epitaxy. We studied dark current and photocurrent as a function of buffer thickness, buffer material, and temperature. A saturation of the dark current with buffer thickness was not observed. The maximum resistance area product was ∼10 Ω cm2 at 295 K. The dark current above 200 K was dominated by generation-recombination current. A pronounced dependence of the photocurrent on the buffer thickness was observed. The peak external quantum efficiency was 46% (at 1.6 μm) without antireflective coating

Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

International Nuclear Information System (INIS)

Nam Hai, Pham; Maruo, Daiki; Tanaka, Masaaki

2014-01-01

We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4 A 2 ( 4 F) → 4 T 1 ( 4 G) and 4 T 1 ( 4 G) → 6 A 1 ( 6 S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs

Radiation damages and electro-conductive characteristics of Neutron-Transmutation-Doped GaAs

Energy Technology Data Exchange (ETDEWEB)

Kuriyama, Kazuo; Sato, Masataka; Sakai, Kiyohiro [Hosei Univ., Koganei, Tokyo (Japan). Coll. of Engineering; Okada, Moritami

1996-04-01

Neutron Transmutation Doping (NTD) method made it possible to do homogeneous doping of impurities and to easily control the doping level. Thus, the method has been put into practice for some materials such as silicon. Here, the annealing behavior of anti-site defects generated in neutron-irradiated GaAs was studied. Electric activations of NTD-impurities were started around 550degC in P1 and P2 radiation fields, which were coincident with the beginning of extinction of electron trapping which was caused by anti-site defects due to fast neutron radiation. The electric resistivities of GaAs in neutron radiation fields; P1, P2 and P3 changed depending with the annealing temperature. The electric resistivities of GaAs in P1 and P2 fields indicate the presence of hopping conduction through radiation damages. The resistance of GaAs irradiated in P1 was smaller by nearly 2 orders than that of the untreated control. Further, the electric activation process for NTD-impurities was investigated using ESR and Raman spectroscopy. (M.N.)

Microfabrication of large-area circular high-stress silicon nitride membranes for optomechanical applications

Directory of Open Access Journals (Sweden)

E. Serra

2016-06-01

Full Text Available In view of the integration of membrane resonators with more complex MEMS structures, we developed a general fabrication procedure for circular shape SiNx membranes using Deep Reactive Ion Etching (DRIE. Large area and high-stress SiNx membranes were fabricated and used as optomechanical resonators in a Michelson interferometer, where Q values up to 1.3 × 106 were measured at cryogenic temperatures, and in a Fabry-Pérot cavity, where an optical finesse up to 50000 has been observed.

Electric characterization of GaAs deposited on porous silicon by electrodeposition technique

International Nuclear Information System (INIS)

Lajnef, M.; Chtourou, R.; Ezzaouia, H.

2010-01-01

GaAs thin films were synthesized on porous Si substrate by the electrodeposition technique. The X-ray diffraction studies showed that the as-grown films were crystallised in mixed phase nature orthorhombic and cubic of GaAs. The GaAs film was then electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) techniques by the way of Al/GaAs Schottky junctions. The electric analysis allowed us to determine the n factor and the barrier height φ b0 parameters of Al/GaAs Schottky junctions. The (C-V) characteristics were recorded at frequency signal 1 MHz in order to identify the effect of the surface states on the behaviour of the capacitance of the device.

Structural and morphological characterizations of ZnO films grown on GaAs substrates by MOCVD

Energy Technology Data Exchange (ETDEWEB)

Agouram, S.; Zuniga Perez, J.; Munoz-Sanjose, V. [Universitat de Valencia, Departamento de Fisica Aplicada y Electromagnetismo, Burjassot (Spain)

2007-07-15

ZnO films were grown on GaAs(100), GaAs(111)A and GaAs(111)B substrates by metal organic chemical vapour deposition (MOCVD). Diethylzinc (DEZn) and tertiarybutanol (t-butanol) were used as Zn and O precursors, respectively. The influence of the growth temperature and GaAs substrate orientation on the crystalline orientation and morphology of the ZnO grown films has been analysed. Crystallinity of grown films was studied by X-ray diffraction (XRD); thickness and morphology of ZnO films were investigated by scanning electron microscopy (SEM). SEM results reveal significant differences between morphologies depending on growth temperature but not significant differences were detected on the texture of grown films. (orig.)

Opto-Mechanical systems design for polarimeter-interferometer on EAST

Energy Technology Data Exchange (ETDEWEB)

Zou, Z.Y. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); University of Science and Technology of China, Hefei, Anhui 230026 (China); Liu, H.Q., E-mail: hqliu@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Ding, W.X.; Brower, D.L. [Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA 90095 (United States); Li, W.M. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Lan, T. [University of Science and Technology of China, Hefei, Anhui 230026 (China); Zeng, L.; Yao, Y.; Yang, Y.; Jie, Y.X. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China)

2016-11-15

Highlights: • The POINT system has been designed double-pass horizontal 11-channel, and the probe beams are reflected by corner cube retro reflectors in the vacuum vessel for the first time. • ZEMAX calculations used to optimize the optical layout design are combined with the mechanical design from CATIA, providing a 3D visualization of the entire POINT system. • The massy, vibration isolation performance of optical table and optical tower are designed and vibration tested. - Abstract: An 11-channel Far-InfaRed (FIR) three-wave POlarimeter-INTerferometer (POINT) system has been successfully operated in 2015 EAST experimental campaign. For high accuracy measurement of POINT system, optimized optical system to reduce the stray light and crosstalk is very important. Optical design is done and improved by using ZEMAX software, in which spot size and energy distribution can be calculated in any position. The crosstalk and stray light can be reduced by optimized design of optical components and putting high extinction ratio materials in some key positions. Vibration isolation coefficient of optical platform is set to 90%. The optical platform and vibration isolation system are about 5 and 20 tons in weight respectively. To reduce vibration caused by the EAST hall, a more than 30 tons in weight stainless steel tower, filled with sand and mounted independent of the EAST machine, is constructed to ensure the stability of optics. Based on the optimized opto-mechanical design, the POINT system resolutions for Faraday rotation and line integral electron density measurements are 0.1° and 1 × 10{sup 16} m{sup −2}, respectively.

Nuclear spin warm up in bulk n -GaAs

Science.gov (United States)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

2016-08-01

We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

Amateurism in an Age of Professionalism: An Empirical Examination of an Irish Sporting Culture: The GAA

Directory of Open Access Journals (Sweden)

Ian Keeler

2013-07-01

This research study recommends that the GAA adopt an innovative approach, through strategic decision-making, to allow the GAA to maintain its amateur ethos, and, yet, successfully compete in the professional sporting market. The strong links with the community must be both nurtured and enhanced. The GAA and Gaelic games must embrace the challenges that the branding success of foreign sports has brought. Player welfare issues for the elite players must be addressed while continuing to protect the club and its amateur structures. The study looks at the key metrics that are required to evolve the GAA. This entails not only focusing on the perceived importance of the amateur ethos to the GAA, but also developing the marketing, branding and profiling of Gaelic games to enhance the performance of an amateur sporting organization in an era of increased professionalism in sport.

Spin-dependent electron many-body effects in GaAs

Science.gov (United States)

Nemec, P.; Kerachian, Y.; van Driel, H. M.; Smirl, Arthur L.

2005-12-01

Time- and polarization-resolved differential transmission measurements employing same and oppositely circularly polarized 150fs optical pulses are used to investigate spin characteristics of conduction band electrons in bulk GaAs at 295K . Electrons and holes with densities in the 2×1016cm-3-1018cm-3 range are generated and probed with pulses whose center wavelength is between 865 and 775nm . The transmissivity results can be explained in terms of the spin sensitivity of both phase-space filling and many-body effects (band-gap renormalization and screening of the Coulomb enhancement factor). For excitation and probing at 865nm , just above the band-gap edge, the transmissivity changes mainly reflect spin-dependent phase-space filling which is dominated by the electron Fermi factors. However, for 775nm probing, the influence of many-body effects on the induced transmission change are comparable with those from reduced phase space filling, exposing the spin dependence of the many-body effects. If one does not take account of these spin-dependent effects one can misinterpret both the magnitude and time evolution of the electron spin polarization. For suitable measurements we find that the electron spin relaxation time is 130ps .

Dynamical properties of tertiarybutylarsine on GaAs(0 0 1) surface

CERN Document Server

Ozeki, M; Tanaka, Y

2002-01-01

The dynamical properties of tertiarybutylarsine (TBA) was studied on GaAs(0 0 1) surface using a supersonic molecular beam. The temperature and incident energy dependence of the reflected beam revealed a reaction channel of TBA on GaAs surface with a large decrease in the activation energy from 2.7 to 1.8 eV as the incident energy increases from 0.04 to 2.5 eV.

Microhardness of epitaxial layers of GaAs doped with rare earths

International Nuclear Information System (INIS)

Kulish, U.M.; Gamidov, Z.S.; Kuznetsova, I.Yu.; Petkeeva, L.N.; Borlikova, G.V.

1989-01-01

Results of the study of microhardness of GaAS layer doped by certain rare earths - Gd, Tb, Dy - are presented. The assumption is made that the higher is the value of the first potential of rare earth impurity ionization (i.e. the higher is the filling of 4f-shell), the lower is the effect of the element on electric and mechanical properties of GaAs epitaxial layers

Doping assessment in GaAs nanowires

DEFF Research Database (Denmark)

Goktas, N. Isik; Fiordaliso, Elisabetta Maria; LaPierre, R. R.

2018-01-01

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p-n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs...

The influence of annealing on manganese implanted GaAs films

International Nuclear Information System (INIS)

Buerger, Danilo; Zhou, Shengqiang; Grenzer, Joerg; Reuther, Helfried; Anwand, Wolfgang; Gottschalch, Volker; Helm, Manfred; Schmidt, Heidemarie

2009-01-01

Besides low-temperature molecular beam epitaxy, ion implantation provides an alternative route to incorporate Mn into GaAs above the equilibrium solubility limit. Recently, Mn implanted GaAs diluted magnetic semiconductor was obtained by pulsed laser annealing. However, post-implantation annealing can lead to the formation of secondary phases. In order to compare the post-annealing effect, we investigate GaMnAs by implanting up to 6 at% Mn followed by rapid thermal and flashlamp annealing. The structural properties were probed by high resolution X-ray diffraction. The magnetic properties were determined by SQUID measurements. Auger electron spectroscopy has been used to profile the depth distribution of Mn in GaAs after implantation and annealing. We elucidate after implantation a loss of As and that during rapid thermal annealing most of the Mn diffuses towards the surface. Flash lamp annealing prevents out-diffusion, but the recrystallisation efficiency is low. Only the flash lamp annealed samples reveal weak ferromagnetism.

An Optomechanical Elevator: Transport of a Bloch Oscillating Bose–Einstein Condensate up and down an Optical Lattice by Cavity Sideband Amplification and Cooling

Directory of Open Access Journals (Sweden)

B. Prasanna Venkatesh

2015-12-01

Full Text Available In this paper we give a new description, in terms of optomechanics, of previous work on the problem of an atomic Bose–Einstein condensate interacting with the optical lattice inside a laser-pumped optical cavity and subject to a bias force, such as gravity. An atomic wave packet in a tilted lattice undergoes Bloch oscillations; in a high-finesse optical cavity the backaction of the atoms on the light leads to a time-dependent modulation of the intracavity lattice depth at the Bloch frequency which can in turn transport the atoms up or down the lattice. In the optomechanical picture, the transport dynamics can be interpreted as a manifestation of dynamical backaction-induced sideband damping/amplification of the Bloch oscillator. Depending on the sign of the pump-cavity detuning, atoms are transported either with or against the bias force accompanied by an up- or down-conversion of the frequency of the pump laser light. We also evaluate the prospects for using the optomechanical Bloch oscillator to make continuous measurements of forces by reading out the Bloch frequency. In this context, we establish the significant result that the optical spring effect is absent and the Bloch frequency is not modified by the backaction.

Investigation on influence parameters in measurements of the optomechanical hole plate using an optical coordinate measuring machine

DEFF Research Database (Denmark)

Morace, Renate Erica; Hansen, Hans Nørgaard; De Chiffre, Leonardo

2003-01-01

This paper describes the results of an experimental investigation on influence parameters in optical coordinate measurements of the optomechanical hole plate. Special attention was paid to the background of the object, which strongly influences the measurement result. Furthermore, it is seen that...... influences, the measurements were all performed with no movements of the axes of the CMM....

Singularities of current-voltage characteristics of GaAs films fabricated by pulsed ions ablation

International Nuclear Information System (INIS)

Kabyshev, A.V.; Konusov, F.V.; Lozhnikov, S.N.; Remnev, G.E.; Saltymakov, M.S.

2009-01-01

A singularities and advantages of the optical, photoelectric and electrical properties of GaAs in comparison with other available materials for electronics, for example, silicon allow to manufacture on it base the devices having an advanced characteristics. The GaAs for electronics, obtained from the dense ablation plasma, possess some preferences as compared to material manufactured by traditional methods of vacuum deposition. The electrical characteristics of GaAs produced by chemical deposition were extensively studied. Purpose of this work is investigation the current-voltage characteristics of thin films of GaAs, deposited on polycrystalline corundum (polycor) from plasma forming the power ions bunch and determination of the thermal vacuum annealing effect on photoelectric and electrical properties of films. Peculiarities of optical, photoelectric and current-voltage characteristics of films obtained by ions ablation are determined by deposition conditions and resistance of initial target GaAs. The transitions between the states with low- and high conduction were revealed directly after deposition in films having the optical properties similar to amorphous materials and/or after annealing in films with properties similar to initial target GaAs. Behavior of current-voltage characteristics at vacuum annealing correlates with Schottky barrier height and photosensitivity and is accompanies of the transport mechanism change. The stable properties of films are formed at its dark conduction 10 -10 -10 -8 s and after annealing at T an =600-700 K. (authors)

Beating quantum limits in an optomechanical sensor by cavity detuning

International Nuclear Information System (INIS)

Arcizet, O.; Briant, T.; Heidmann, A.; Pinard, M.

2006-01-01

We study the quantum limits in an optomechanical sensor based on a detuned high-finesse cavity with a movable mirror. We show that the radiation pressure exerted on the mirror by the light in the detuned cavity induces a modification of the mirror dynamics and makes the mirror motion sensitive to the signal. This leads to an amplification of the signal by the mirror dynamics, and to an improvement of the sensor sensitivity beyond the standard quantum limit, up to an ultimate quantum limit only related to the mechanical dissipation of the mirror. This improvement is somewhat similar to the one predicted in detuned signal-recycled gravitational-wave interferometers, and makes a high-finesse cavity a model system to test these quantum effects

Lateral n-p-n bipolar transistors by ion implantation into semi-insulating GaAs

International Nuclear Information System (INIS)

Canfield, P.; Forbes, L.

1988-01-01

GaAs bipolar transistors have not seen the major development effort that GaAs MESFETs have due primarily to the short minority carrier lifetimes in GaAs. The short minority carrier lifetimes require that the base region be very thin which, if done by implantation, requires that the doping be high to obtain a well defined base profile. These requirements are very difficult to achieve in GaAs and typically, if high current gain and high speed are desired for a bipolar technology, then heterostructure bipolars are the appropriate technology, although the cost of heterostructure devices will be prohibitive for some time to come. For applications requiring low current gain, more modest fabrication rules can be followed. Lateral bipolars are particularly attractive since they would be easier to fabricate than a planar bipolar or a heterojunction bipolar. Lateral bipolars do not require steps or deep contacts to make contact with the subcollector or highly doped very thin epilayers for the base region and they can draw upon the semi-insulating properties of the GaAs substrates for device isolation. Bipolar transistors are described and shown to work successfully. (author)

Neutron-damaged GaAs detectors for use in a Compton spectrometer

International Nuclear Information System (INIS)

Kammeraad, J.E.; Sale, K.E.; Wang, C.L.; Baltrusaitis, R.M.

1992-01-01

Detectors made of GaAs are being studies for use on the focal plane of a Compton spectrometer which measures 1-MeV to 25-MeV gamma rays with high energy resolution (1% or 100 keV, whichever is greater) and 200-ps time resolution. The detectors are GaAs chips that have been neutron-damaged to improve the time response. The detectors will be used to measure fast transient signals in the current mode. The properties of various GaAs detector configurations are being studied by bombarding sample detectors with short pulses of 4-MeV to 16-MeV electrons at the Linac Facility at EG ampersand G Energy Measurements, Inc., Santa Barbara Operations. Measurements of detector sensitivity and impulse response versus detector bias, thickness, and electron beam energy and intensity have been performed and are presented. 5 refs

Sub-wavelength metamaterial cylinders with multiple dipole resonances

DEFF Research Database (Denmark)

Arslanagic, Samel; Breinbjerg, Olav

2009-01-01

It has been shown that the sub-wavelength resonances of the individual MTM cylinders also occur for electrically small configurations combining 2 or 4 cylinders. For the 2-and 4-cylinder configurations the overall size is 1/20 and 1/12.5 of the smallest wavelength, respectively. These MTM...... configuration thus offer the possibility for multi-resonant electrically small configurations....

ITER TASK T252 (1995):Gamma radiation testing of a GaAs operational amplifier for instrument applications

International Nuclear Information System (INIS)

Hiemstra, D.

1996-03-01

The purpose of this 1995 ITER task was : to build an improved operational amplifier using GaAs MESFET technology, to build a reference voltage subcircuit using GaAs MESFET technology and to investigate the potential of GaAs HBT's to improve the noise performance of the GaAs MESFET operational amplifier. This work addresses the need for instrumentation-grade components to read sensors in an experimental fusion reactor, where the anticipated total dose for a useful service life is 3Grad(GaAs). It is an extension of our 1994 work. 3 tabs., 6 figs

Quantum entanglement and teleportation in pulsed cavity optomechanics

Energy Technology Data Exchange (ETDEWEB)

Hofer, Sebastian G. [Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Institute for Theoretical Physics, Institute for Gravitational Physics, Leibniz University Hannover, Callinstrasse 38, 30167 Hannover (Germany); Wieczorek, Witlef; Aspelmeyer, Markus [Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Hammerer, Klemens [Institute for Theoretical Physics, Institute for Gravitational Physics, Leibniz University Hannover, Callinstrasse 38, 30167 Hannover (Germany)

2011-11-15

Entangling a mechanical oscillator with an optical mode is an enticing and yet a very challenging goal in cavity optomechanics. Here we consider a pulsed scheme to create Einstein-Podolsky-Rosen-type entanglement between a traveling-wave light pulse and a mechanical oscillator. The entanglement can be verified unambiguously by a pump-probe sequence of pulses. In contrast to schemes that work in a steady-state regime under a continuous-wave drive, this protocol is not subject to stability requirements that normally limit the strength of achievable entanglement. We investigate the protocol's performance under realistic conditions, including mechanical decoherence, in full detail. We discuss the relevance of a high mechanical Qf product for entanglement creation and provide a quantitative statement on which magnitude of the Qf product is necessary for a successful realization of the scheme. We determine the optimal parameter regime for its operation and show it to work in current state-of-the-art systems.

Analysis of the modified optical properties and band structure of GaAs1-xSbx-capped InAs/GaAs quantum dots

NARCIS (Netherlands)

Ulloa, J.M.; Llorens, J.M.; Moral, del M.; Bozkurt, M.; Koenraad, P.M.; Hierro, A.

2012-01-01

The origin of the modified optical properties of InAs/GaAs quantum dots (QD) capped with a thin GaAs1-xSbx layer is analyzed in terms of the band structure. To do so, the size, shape, and composition of the QDs and capping layer are determined through cross-sectional scanning tunnelling microscopy

Basic mechanisms study for MIS solar cell structures on GaAs

Science.gov (United States)

Fonash, S. J.

1978-01-01

The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

Photoelectrochemical Water Oxidation by GaAs Nanowire Arrays Protected with Atomic Layer Deposited NiO x Electrocatalysts

Science.gov (United States)

Zeng, Joy; Xu, Xiaoqing; Parameshwaran, Vijay; Baker, Jon; Bent, Stacey; Wong, H.-S. Philip; Clemens, Bruce

2018-02-01

Photoelectrochemical (PEC) hydrogen production makes possible the direct conversion of solar energy into chemical fuel. In this work, PEC photoanodes consisting of GaAs nanowire (NW) arrays were fabricated, characterized, and then demonstrated for the oxygen evolution reaction (OER). Uniform and periodic GaAs nanowire arrays were grown on a heavily n-doped GaAs substrates by metal-organic chemical vapor deposition selective area growth. The nanowire arrays were characterized using cyclic voltammetry and impedance spectroscopy in a non-aqueous electrochemical system using ferrocene/ferrocenium (Fc/Fc+) as a redox couple, and a maximum oxidation photocurrent of 11.1 mA/cm2 was measured. GaAs NW arrays with a 36 nm layer of nickel oxide (NiO x ) synthesized by atomic layer deposition were then used as photoanodes to drive the OER. In addition to acting as an electrocatalyst, the NiO x layer served to protect the GaAs NWs from oxidative corrosion. Using this strategy, GaAs NW photoanodes were successfully used for the oxygen evolution reaction. This is the first demonstration of GaAs NW arrays for effective OER, and the fabrication and protection strategy developed in this work can be extended to study any other nanostructured semiconductor materials systems for electrochemical solar energy conversion.

Electric characterization of GaAs deposited on porous silicon by electrodeposition technique

Energy Technology Data Exchange (ETDEWEB)

Lajnef, M., E-mail: Mohamed.lajnef@yahoo.fr [Laboratoire de Photovoltaique et de Semi-conducteurs, Centre de Recherche et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia); Chtourou, R.; Ezzaouia, H. [Laboratoire de Photovoltaique et de Semi-conducteurs, Centre de Recherche et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

2010-03-01

GaAs thin films were synthesized on porous Si substrate by the electrodeposition technique. The X-ray diffraction studies showed that the as-grown films were crystallised in mixed phase nature orthorhombic and cubic of GaAs. The GaAs film was then electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) techniques by the way of Al/GaAs Schottky junctions. The electric analysis allowed us to determine the n factor and the barrier height {phi}{sub b0} parameters of Al/GaAs Schottky junctions. The (C-V) characteristics were recorded at frequency signal 1 MHz in order to identify the effect of the surface states on the behaviour of the capacitance of the device.

Nitride surface passivation of GaAs nanowires: impact on surface state density.

Science.gov (United States)

Alekseev, Prokhor A; Dunaevskiy, Mikhail S; Ulin, Vladimir P; Lvova, Tatiana V; Filatov, Dmitriy O; Nezhdanov, Alexey V; Mashin, Aleksander I; Berkovits, Vladimir L

2015-01-14

Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (μ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the μ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

MOCVD growth of CdTe and HgTe on GaAs in a vertical, high-speed, rotating-disc reactor

International Nuclear Information System (INIS)

Tompa, G.S.; Nelson, C.R.; Reinert, P.D.; Saracino, M.A.; Terrill, L.A.; Colter, P.C.

1989-01-01

The metalorganic chemical vapor deposition (MOCVD) growth of CdTe and HgTe on GaAs (111) and (100) substrates in a vertical, high-speed, rotating-disc reactor was investigated. A range of total reactor pressure, carrier gas flow rate, chemical concentrations, deposition temperature, and rotation rate have been investigated in an attempt to optimize growth conditions. Diisopropyltelluride (DIPTe) and Dimethylcadmium (DMCd) were used as growth precursors. Thickness uniformity varies less than +/- 1.5% over 50 mm diameter wafers. Films having FWHM X-ray rocking curves less than 90 arcsec were obtained on GaAs (111) substrates. The films have excellent surface morphology, exhibiting less than 5 x 10 4 cm - 2 orange peel dents which are much-lt 1 μm in size. An elemental mercury source was added to the growth system. Initial results for the growth of HgTe and HgCdTe are discussed

X-ray electron density distribution of GaAs

International Nuclear Information System (INIS)

Pietsch, U.

1986-01-01

Using ten X-ray structure amplitudes of strong reflections and nine weak reflections both, the valence electron and the difference electron density distribution of GaAs, are calculated. The experimental data are corrected for anomalous dispersion using a bond charge model. The calculated plots are compared with up to now published band structure-based and semiempirically calculated density plots. Taking into account the experimental data of germanium, measured on the same absolute scale, the difference density between GaAs and Ge is calculated. This exhibits the charge transfer between both the f.c.c.-sublattices as well as both, the shift and the decrease of the bond charge, quite closely connected to the theoretical results published by Baur et al. (author)

Electrical properties of Ga ion beam implanted GaAs epilayer

International Nuclear Information System (INIS)

Hirayama, Yoshiro; Okamoto, Hiroshi

1985-01-01

Resistivity enhancement by 5 orders or more was realized by Ga focused ion beam implantation into n + and p + GaAs epilayers. For originally n + epilayers, this resistivity enhancement is maintained after annealing as high as 800 deg C. However this enhancement disappears after annealing at above 650 deg C for p + epilayer. This property makes GaAs high resistive only in a limited area whose minimum dimension is 0.1 μm or less, and is attractive for a device fabrication process to electrically isolate integrated elements. (author)

Polarization measurement by use of discrete space-variant sub wavelength dielectric gratings

International Nuclear Information System (INIS)

Biener, G.; Niv, A.; Gorodetski, Yu.; Kleiner, V.; Hasman, E.

2004-01-01

Full Text:Polarization measurement has been widely used for a large range of applications such as ellipsometry bio-imaging, imaging polarimetry and optical communications. A commonly used method is measuring of the time-dependent signal once the beam is transmitted through a photoelastic modulator or a rotating quarter-wave plate followed by an analyzer. The polarization state of the beam can be derived by Fourier analysis of the detected signal. This method, however, requires a sequence of consecutive measurements, thus making it impractical for real-time polarization measurement in an application such as adaptive polarization-mode dispersion compensation in optical communications. Recently, we developed a novel method for real-time polarization measurement by use of a discrete space-variant sub wavelength dielectric grating (DSG). The formation of the grating is done by discrete orientation of the local sub wavelength grooves. The complete polarization analysis of the incident beam is determined by spatial Fourier transform of the near-field intensity distribution transmitted through the DSG followed by a sub wavelength metal polarizer. We realized the gratings for CO 2 laser radiation at a wavelength of 10.6 micron on GaAs substrate utilizing advanced photo lithographic and etching techniques. We experimentally demonstrated the ability of our method to measure the polarization state for fully and partially polarized light. Unlike other methods based on Fourier analysis, no active elements are required. It is possible to integrate our polarimeter on a two-dimensional detector array for lab-on chip applications to achieve a high-throughput and low-cost commercial polarimeter for bio sensing. Currently we are investigating the possibility of using far-field measurement of the beam emerging from a DSG for polarization measurement

Scanning microwave microscopy applied to semiconducting GaAs structures

Science.gov (United States)

Buchter, Arne; Hoffmann, Johannes; Delvallée, Alexandra; Brinciotti, Enrico; Hapiuk, Dimitri; Licitra, Christophe; Louarn, Kevin; Arnoult, Alexandre; Almuneau, Guilhem; Piquemal, François; Zeier, Markus; Kienberger, Ferry

2018-02-01

A calibration algorithm based on one-port vector network analyzer (VNA) calibration for scanning microwave microscopes (SMMs) is presented and used to extract quantitative carrier densities from a semiconducting n-doped GaAs multilayer sample. This robust and versatile algorithm is instrument and frequency independent, as we demonstrate by analyzing experimental data from two different, cantilever- and tuning fork-based, microscope setups operating in a wide frequency range up to 27.5 GHz. To benchmark the SMM results, comparison with secondary ion mass spectrometry is undertaken. Furthermore, we show SMM data on a GaAs p-n junction distinguishing p- and n-doped layers.

Formation, atomic structure, and electronic properties of GaSb quantum dots in GaAs

Energy Technology Data Exchange (ETDEWEB)

Timm, R.

2007-12-14

In this work, cross-sectional scanning tunneling microscopy and spectroscopy are used for the first time to study the shape, size, strain, chemical composition, and electronic properties of capped GaSb/GaAs QDs at the atomic scale. By evaluating such structural results on a variety of nanostructures built using different epitaxy methods and growth conditions, details on the underlying QD formation processes can be revealed. A cross-over from flat quantum wells (QWs) to optically active QDs can be observed in samples grown by metalorganic chemical vapor deposition (MOCVD) with increasing amount of GaSb, including self-assembled Sb accumulations within a still two-dimensional layer and tiny three-dimensional GaSb islands probably acting as precursor structures. The QWs consist of significantly intermixed material with stoichiometries of maximally 50% GaSb, additionally exhibiting small gaps filled with GaAs. A higher GaSb content up to nearly pure material is found in the QDs, being characterized by small sizes of up to 8 nm baselength and about 2 nm height. In spite of the intermixing, all nanostructures have rather abrupt interfaces, and no significant Sb segregation in growth direction is observed. This changes completely when molecular beam epitaxy (MBE) is used as growth method, in which case individual Sb atoms are found to be distributed over several nm above the nanostructures. Massive group-V atomic exchange processes are causing this strong inter-mixing and Sb segregation during GaAs overgrowth. In combination with the large strain inherent to GaSb/GaAs QDs, this segregation upon overgrowth is assumed to be the reason for a unique structural phenomenon: All MBE-grown QDs, independent of the amount of deposited GaSb, exhibit a ring structure, consisting of a ring body of high GaSb content and a more or less extended central gap filled with GaAs. These rings have formed in a self-assembled way even when the initial GaSb layer was overgrown considerably fast

Simulated and experimental spectroscopic performance of GaAs X-ray pixel detectors

International Nuclear Information System (INIS)

Bisogni, M.G.; Cola, A.; Fantacci, M.E.

2001-01-01

In pixel detectors, the electrode geometry affects the signal shape and therefore the spectroscopic performance of the device. This effect is enhanced in semiconductors where carrier trapping is relevant. In particular, semi insulating (SI) GaAs crystals present an incomplete charge collection due to a high concentration of deep traps in the bulk. In the last few years, SI GaAs pixel detectors have been developed as soft X-ray detectors for medical imaging applications. In this paper, we present a numerical method to evaluate the local charge collection properties of pixel detectors. A bi-dimensional description has been used to represent the detector geometry. According to recent models, the active region of a reverse biased SI GaAs detector is almost neutral. Therefore, the electrostatic potential inside a full active detector has been evaluated using the Laplace equation. A finite difference method with a fixed step orthogonal mesh has been adopted. The photon interaction point has been generated with a Monte Carlo method according to the attenuation length of a monochromatic X-ray beam in GaAs. The number of photogenerated carriers for each interaction has been extracted using a gaussian distribution. The induced signal on the collecting electrode has been calculated according to the Ramo's theorem and the trapping effect has been modeled introducing electron and hole lifetimes. The noise of the charge preamplifier have been also taken into account. A comparison between simulated and experimental X-ray spectra from a 241 Am source acquired with different GaAs pixel detectors has been carried out

Towards low-dimensional hole systems in Be-doped GaAs nanowires

DEFF Research Database (Denmark)

Ullah, A. R.; Gluschke, J. G.; Jeppesen, Peter Krogstrup

2017-01-01

-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good......GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly confined 0D and 1D hole systems with strong spin–orbit effects, motivating...... our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top...

Resistance Fluctuations in GaAs Nanowire Grids

Directory of Open Access Journals (Sweden)

Ivan Marasović

2014-01-01

Full Text Available We present a numerical study on resistance fluctuations in a series of nanowire-based grids. Each grid is made of GaAs nanowires arranged in parallel with metallic contacts crossing all nanowires perpendicularly. Electrical properties of GaAs nanowires known from previous experimental research are used as input parameters in the simulation procedure. Due to the nonhomogeneous doping, the resistivity changes along nanowire. Allowing two possible nanowire orientations (“upwards” or “downwards”, the resulting grid is partially disordered in vertical direction which causes resistance fluctuations. The system is modeled using a two-dimensional random resistor network. Transfer-matrix computation algorithm is used to calculate the total network resistance. It is found that probability density function (PDF of resistance fluctuations for a series of nanowire grids changes from Gaussian behavior towards the Bramwell-Holdsworth-Pinton distribution when both nanowire orientations are equally represented in the grid.

A new structure for comparing surface passivation materials of GaAs solar cells

Science.gov (United States)

Desalvo, Gregory C.; Barnett, Allen M.

1989-01-01

The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

Effect of InGaAs interlayer on the properties of GaAs grown on Si (111) substrate by molecular beam epitaxy

International Nuclear Information System (INIS)

Wen, Lei; Gao, Fangliang; Li, Jingling; Guan, Yunfang; Wang, Wenliang; Zhou, Shizhong; Lin, Zhiting; Zhang, Xiaona; Zhang, Shuguang; Li, Guoqiang

2014-01-01

High-quality GaAs films have been epitaxially grown on Si (111) substrates by inserting an In x Ga 1−x As interlayer with proper In composition by molecular beam epitaxy (MBE). The effect of In x Ga 1−x As (0 < x < 0.2) interlayers on the properties of GaAs films grown on Si (111) substrates by MBE has been studied in detailed. Due to the high compressive strain between InGaAs and Si, InGaAs undergoes partial strain relaxation. Unstrained InGaAs has a larger lattice constant than GaAs. Therefore, a thin InGaAs layer with proper In composition may adopt a close lattice constant with that of GaAs, which is beneficial to the growth of high-quality GaAs epilayer on top. It is found that the proper In composition in In x Ga 1−x As interlayer of 10% is beneficial to obtaining high-quality GaAs films, which, on the one hand, greatly compensates the misfit stress between GaAs film and Si substrate, and on the other hand, suppresses the formation of multiple twin during the heteroepitaxial growth of GaAs film. However, when the In composition does not reach the proper value (∼10%), the In x Ga 1−x As adopts a lower strain relaxation and undergoes a lattice constant smaller than unstrained GaAs, and therefore introduces compressive stress to GaAs grown on top. When In composition exceeds the proper value, the In x Ga 1−x As will adopt a higher strain relaxation and undergoes a lattice constant larger than unstrained GaAs, and therefore introduces tensile stress to GaAs grown on top. As a result, In x Ga 1−x As interlayers with improper In composition introduces enlarged misfit stress to GaAs epilayers grown on top, and deteriorates the quality of GaAs epilayers. This work demonstrates a simple but effective method to grow high-quality GaAs epilayers and brings up a broad prospect for the application of GaAs-based optoelectronic devices on Si substrates

Dual-wavelength phase-shifting digital holography selectively extracting wavelength information from wavelength-multiplexed holograms.

Science.gov (United States)

Tahara, Tatsuki; Mori, Ryota; Kikunaga, Shuhei; Arai, Yasuhiko; Takaki, Yasuhiro

2015-06-15

Dual-wavelength phase-shifting digital holography that selectively extracts wavelength information from five wavelength-multiplexed holograms is presented. Specific phase shifts for respective wavelengths are introduced to remove the crosstalk components and extract only the object wave at the desired wavelength from the holograms. Object waves in multiple wavelengths are selectively extracted by utilizing 2π ambiguity and the subtraction procedures based on phase-shifting interferometry. Numerical results show the validity of the proposed technique. The proposed technique is also experimentally demonstrated.

Accelerated GaAs growth through MOVPE for low-cost PV applications

Science.gov (United States)

Ubukata, Akinori; Sodabanlu, Hassanet; Watanabe, Kentaroh; Koseki, Shuichi; Yano, Yoshiki; Tabuchi, Toshiya; Sugaya, Takeyoshi; Matsumoto, Koh; Nakano, Yoshiaki; Sugiyama, Masakazu

2018-05-01

The high growth rate of epitaxial GaAs was investigated using a novel horizontal metalorganic vapor phase epitaxy (MOVPE) reactor, from the point of view of realizing low-cost photovoltaic (PV) solar cells. The GaAs growth rate exhibited an approximately linear relationship with the amount of trimethylgalium (TMGa) supplied, up to a rate of 90 μm/h. The distribution of growth rate was observed for a two-inch wafer, along the flow direction, and the normalized profile of the distribution was found to be independent of the precursor input, from 20 to 70 μm/h. These tendencies indicated that significant parasitic prereaction did not occur in the gaseous phase, for this range of growth rate. GaAs p-n single-junction solar cells were successfully fabricated at growth rates of 20, 60, and 80 μm/h. The conversion efficiency of the cell grown at 80 μm/h was comparable to that of the 20 μm/h cell, indicating the good quality and properties of GaAs. The epitaxial growth exhibited good uniformity, as evidenced by the uniformity of the cell performance across the wafer, from the center to the edge. The result indicated the potential of high-throughput MOVPE for low-cost production, not only for PV devices but also for other semiconductor applications.

Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

Directory of Open Access Journals (Sweden)

Fedorov A

2010-01-01

Full Text Available Abstract We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background.

Inducer-independent production of pectinases in Aspergillus niger by overexpression of the D-galacturonic acid-responsive transcription factor gaaR.

Science.gov (United States)

Alazi, Ebru; Knetsch, Tim; Di Falco, Marcos; Reid, Ian D; Arentshorst, Mark; Visser, Jaap; Tsang, Adrian; Ram, Arthur F J

2018-03-01

The transcription factor GaaR is needed for the expression of genes required for pectin degradation and transport and catabolism of the main degradation product, D-galacturonic acid (GA) in Aspergillus niger. In this study, we used the strong constitutive gpdA promoter of Aspergillus nidulans to overexpress gaaR in A. niger. Overexpression of gaaR resulted in an increased transcription of the genes encoding pectinases, (putative) GA transporters, and catabolic pathway enzymes even under non-inducing conditions, i.e., in the absence of GA. Exoproteome analysis of a strain overexpressing gaaR showed that this strain secretes highly elevated levels of pectinases when grown in fructose. The genes encoding exo-polygalacturonases were found to be subjected to CreA-mediated carbon catabolite repression, even in the presence of fructose. Deletion of creA in the strain overexpressing gaaR resulted in a further increase in pectinase production in fructose. We showed that GaaR localizes mainly in the nucleus regardless of the presence of an inducer, and that overexpression of gaaR leads to an increased concentration of GaaR in the nucleus.

Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

Science.gov (United States)

Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

2012-07-01

Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

Nanoscale footprints of self-running gallium droplets on GaAs surface.

Directory of Open Access Journals (Sweden)

Jiang Wu

Full Text Available In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001 surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems.

Polaron binding energy and effective mass in the GaAs film

International Nuclear Information System (INIS)

Wu Zhenhua; Yan Liangxing; Tian Qiang; Li Hua; Liu Bingcan

2012-01-01

The binding energy and effective mass of a polaron in a GaAs film deposited on the Al 0.3 Ga 0.7 As substrate are studied theoretically by using the fractional-dimensional space approach. Our calculations show that the polaron binding energy and mass shift decrease monotonously with increasing the film thickness. For the film thicknesses with L w ≤ 70Å and the substrate thicknesses with L b ≤ 200Å, the different values of the substrate thickness influence the polaron binding energy and mass shift in the GaAs film. The polaron binding energy and mass shift increase monotonously with increasing the substrate thickness. For the film thickness with L w ≥ 70Å or the substrate thicknesses with L b ≤ 200Å, the different values of the substrate thickness have no significant influence on the polaron binding energy and mass shift in the GaAs film deposited on the Al 0.3 Ga 0.7 As substrate.

Sulfidic photochemical passivation of GaAs surfaces in alcoholic solutions

International Nuclear Information System (INIS)

Simonsmeier, T.; Ivankov, A.; Bauhofer, W.

2005-01-01

We report on a remarkable enhancement of the passivation effect of sulfidic solutions through illumination with above band gap light. Luminescence measurements on GaAs surfaces which have been illuminated during chemical passivation reveal in comparison to nonilluminated samples a further reduction of their surface density of states as well as a significantly increased stability of the passivation. Investigations with photoelectron spectroscopy show that illumination leads to a nearly complete removal of oxides on the surface. Measurements on Schottky diodes which have been manufactured with photochemically passivated GaAs indicate a noticeable decrease in band bending and a depinning of the Fermi level

Pulse GaAs field transistor amplifier with subnanosecond time transient

International Nuclear Information System (INIS)

Sidnev, A.N.

1987-01-01

Pulse amplifier on fast field effect GaAs transistors with Schottky barrier is described. The amplifier contains four cascades, the first three of which are made on combined transistors on the common-drain circuit. The last cascade is made on high-power field effect GaAs transistor for coordination with 50 ohm load. The amplifier operates within the range of input signals from 0.5 up to 100 mV with repetition frequency up to 16 Hz, The gain of the amplifier is ≅ 20 dB. The setting time at output pulses amplitude up to 1 V constitutes ∼ 0.2 ns

Modeling and Design of Graphene GaAs Junction Solar Cell

Directory of Open Access Journals (Sweden)

Yawei Kuang

2015-01-01

Full Text Available Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work.

Surface science analysis of GaAs photocathodes following sustained electron beam delivery

Directory of Open Access Journals (Sweden)

V. Shutthanandan

2012-06-01

Full Text Available Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL. Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS, atomic force microscopy, and secondary ion mass spectrometry (SIMS. In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

Solvent-mediated self-assembly of hexadecanethiol on GaAs (0 0 1)

International Nuclear Information System (INIS)

Huang, Xiaohuan; Dubowski, Jan J.

2014-01-01

Graphical abstract: - Highlights: • Outstanding quality hexadecanethiol self-assembled monolayers (HDT SAM) produced on GaAs (0 0 1) due to the mediated role of water in an alcoholic environment. • HDT SAM formed in chloroform exhibit excellent electronic passivation properties in contrast to their structural characteristics. • Low dielectric constant solvents do not necessary provide conditions advantageous for the formation of high quality alkanethiol SAM. • Photoluminescence emitting materials allow to investigate the mechanisms of both electronic and chemical passivation and, thus, they are an excellent platform for studying the mechanisms of SAM formation on solid substrates. - Abstract: We have investigated the influence of solvents on the quality of hexadecanethiol (HDT) self-assembled monolayers (SAM) formed on GaAs (0 0 1) in chloroform, ethanol and ethanol/water 1:1 characterized by their increasing dielectric constants from 4.8 (chloroform) to 24.5 (ethanol) and water (80.1). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data show that the incubation in ethanol/water 1:1 solution creates conditions favouring inter-molecular interaction leading to the formation of an outstanding quality HDT SAM on GaAs (0 0 1). Incubation in low-dielectric constant solvents is not offering advantageous conditions for growing HDT SAM on GaAs. The chloroform environment, while weakening the thiol–thiol interaction, induces the oxidation of the GaAs surface and, in particular, formation of Ga 2 O 3 . This reduces the concentration of surface defects responsible for non-radiative recombination and leads to an enhanced photoluminescence emission, despite the fact that HDT SAM formed in chloroform are highly disordered, exhibiting the worst chemical passivation among the investigated samples

Single-Crystal Y2O3 Epitaxially on GaAs(001 and (111 Using Atomic Layer Deposition

Directory of Open Access Journals (Sweden)

Y. H. Lin

2015-10-01

Full Text Available Single-crystal atomic-layer-deposited (ALD Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films 2 nm thick were epitaxially grown on molecular beam epitaxy (MBE GaAs(001-4 \\(\\times\\ 6 and GaAs(111A-2 \\(\\times\\ 2 reconstructed surfaces. The in-plane epitaxy between the ALD-oxide films and GaAs was observed using \\textit{in-situ} reflection high-energy electron diffraction in our uniquely designed MBE/ALD multi-chamber system. More detailed studies on the crystallography of the hetero-structures were carried out using high-resolution synchrotron radiation X-ray diffraction. When deposited on GaAs(001, the Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films are of a cubic phase and have (110 as the film normal, with the orientation relationship being determined: Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\(\\(110\\[\\(001\\][\\(\\overline{1}10\\]//GaAs(\\(001\\[\\(110\\][\\(1\\overline{1}0\\]. On GaAs(\\(111\\A, the Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films are also of a cubic phase with (\\(111\\ as the film normal, having the orientation relationship of Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\(\\(111\\[\\(2\\overline{1}\\overline{1}\\] [\\(01\\overline{1}\\]//GaAs (\\(111\\ [\\(\\overline{2}11\\][\\(0\\overline{1}1\\]. The relevant orientation for the present/future integrated circuit platform is (\\(001\\. The ALD-Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\/GaAs(\\(001\\-4 \\(\\times\\ 6 has shown excellent electrical properties. These include small frequency dispersion in the capacitance-voltage CV curves at accumulation of ~7% and ~14% for the respective p- and n-type samples with the measured frequencies of 1 MHz to 100 Hz. The interfacial trap density (Dit is low of ~10\\(^{12}\\ cm\\(^{−2}\\eV\\(^{−1}\\ as extracted from measured quasi-static CVs. The frequency dispersion at accumulation and the D\\(_{it}\\ are the lowest ever achieved among all the ALD-oxides on GaAs(\\(001\\.

High-Performance GaAs Nanowire Solar Cells for Flexible and Transparent Photovoltaics.

Science.gov (United States)

Han, Ning; Yang, Zai-xing; Wang, Fengyun; Dong, Guofa; Yip, SenPo; Liang, Xiaoguang; Hung, Tak Fu; Chen, Yunfa; Ho, Johnny C

2015-09-16

Among many available photovoltaic technologies at present, gallium arsenide (GaAs) is one of the recognized leaders for performance and reliability; however, it is still a great challenge to achieve cost-effective GaAs solar cells for smart systems such as transparent and flexible photovoltaics. In this study, highly crystalline long GaAs nanowires (NWs) with minimal crystal defects are synthesized economically by chemical vapor deposition and configured into novel Schottky photovoltaic structures by simply using asymmetric Au-Al contacts. Without any doping profiles such as p-n junction and complicated coaxial junction structures, the single NW Schottky device shows a record high apparent energy conversion efficiency of 16% under air mass 1.5 global illumination by normalizing to the projection area of the NW. The corresponding photovoltaic output can be further enhanced by connecting individual cells in series and in parallel as well as by fabricating NW array solar cells via contact printing showing an overall efficiency of 1.6%. Importantly, these Schottky cells can be easily integrated on the glass and plastic substrates for transparent and flexible photovoltaics, which explicitly demonstrate the outstanding versatility and promising perspective of these GaAs NW Schottky photovoltaics for next-generation smart solar energy harvesting devices.

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

Science.gov (United States)

Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

2014-12-01

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Influence of magnetic and ultrasonic fields on coefficient of reflectivity of GaAs, GaSb and InAs crystals

International Nuclear Information System (INIS)

Zaveryukhin, B.N.; Zaveryukhina, N.N.; Zaveryukhina, E.V.; Volodarskiy, V.V.

2007-01-01

Full text: Previously we demonstrated for the first time in the world that ultrasonic waves of the megahertz range can change the transport properties and a structure of semiconductors. In this work we have experimentally studied the influence of ultrasonic treatment on the spectral coefficients of reflection R in the magnetic fields of the samples of GaAs-, GaSb- and InAs-crystals. The reflectance spectra in the magnetic field of the samples before and after the ultrasonic treatment (UST) for a certain time were measured in a broad wavelength range including ultraviolet, visible, and infrared spectral regions. The semi-insulating GaAs-crystals had a thickness d=100 μm and a working area S of up to 3sm 2 . The p-GaSb- crystals had an area of S=0.25sm 2 and d =250 μm. The base p-GaSb-layers possessed the concentration N=2·10 17 sm 3 and n-GaSb-layers with a thickness of 0.5 m were created by diffusion doping with phosphorus. Besides, the experiments were performed also for of the n-InAs-crystals. The samples of the InAs-n crystals had a thickness of 100 μm an area S = 0.25 sm 2 . Some remains of sulfuric (S) were discovered in InAs-samples. As could was see from the experiments, all the initial IR spectra measured for the samples with various dopant concentrations NP exhibit maximums (peaks) for 0.2 μm and minimum (holes) for. The reflectance spectra measured after UST for time of t > l hour clearly reveal a shift of the R minima toward longer wavelengths and a general decrease in the reflectance of each sample. The shift of the R is unambiguous evidence of the acoustically stimulated diffusion of impurity (phosphorus) inward of the samples. Discovered peaks and holes slitted and changed their sizes in the magnetic fields. It should be emphasized that behavior of the R spectra of the GaAs-, In As- and GaSb- samples is determined by the same mechanisms. Changes of the R spectra after the UST are explained by acoustically stimulated diffusion of the dopant inward

Coalescence of GaAs on (001) Si nano-trenches based on three-stage epitaxial lateral overgrowth

Energy Technology Data Exchange (ETDEWEB)

He, Yunrui; Wang, Jun, E-mail: wangjun12@bupt.edu.cn; Hu, Haiyang; Wang, Qi; Huang, Yongqing; Ren, Xiaomin [State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

2015-05-18

The coalescence of selective area grown GaAs regions has been performed on patterned 1.8 μm GaAs buffer layer on Si via metal-organic chemical vapor deposition. We propose a promising method of three-stage epitaxial lateral overgrowth (ELO) to achieve uniform coalescence and flat surface. Rough surface caused by the coalescence of different growth fronts is smoothened by this method. Low root-mean-square surface roughness of 6.29 nm has been obtained on a 410-nm-thick coalesced ELO GaAs layer. Cross-sectional transmission electron microscope study shows that the coalescence of different growth fronts will induce some new dislocations. However, the coalescence-induced dislocations tend to mutually annihilate and only a small part of them reach the GaAs surface. High optical quality of the ELO GaAs layer has been confirmed by low temperature (77 K) photoluminescence measurements. This research promises a very large scale integration platform for the monolithic integration of GaAs-based device on Si.

Self-assisted GaAs nanowires with selectable number density on Silicon without oxide layer

International Nuclear Information System (INIS)

Bietti, S; Somaschini, C; Esposito, L; Sanguinetti, S; Frigeri, C; Fedorov, A; Geelhaar, L

2014-01-01

We present the growth of self-assisted GaAs nanowires (NWs) with selectable number density on bare Si(1 1 1), not covered by the silicon oxide. We determine the number density of the NWs by initially self-assembling GaAs islands on whose top a single NW is nucleated. The number density of the initial GaAs base islands can be tuned by droplet epitaxy and the same degree of control is then transferred to the NWs. This procedure is completely performed during a single growth in an ultra-high vacuum environment and requires neither an oxide layer covering the substrate, nor any pre-patterning technique. (paper)

Low energy Ar ion bombardment damage of Si, GaAs, and InP surfaces

International Nuclear Information System (INIS)

Williams, R.S.

1982-01-01

Argon bombardment damage to (100) surfaces of Si, GaAs, and InP for sputter ion-gun potentials of 1, 2, and 3 kilovolts was studied using Rutherford backscattering. Initial damage rates and saturation damage levels were determined. Bombardment damage sensitivity increased for the sequence Si, GaAs, and InP. Saturation damage levels for Si and GaAs correspond reasonably to LSS projected range plus standard deviation estimates; damage to InP exceeded this level significantly. For an ion-gun potential of 3 keV, the initial sputter yield of P from an InP surface exceeded the sputter yield of In by four atoms per incident Ar projectile. (author)

Interband emission energy in a dilute nitride quaternary semiconductor quantum dot for longer wavelength applications

Science.gov (United States)

Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo; Duque, C. A.

2016-07-01

Excitonic properties are studied in a strained Ga1-xInxNyAs1-y/GaAs cylindrical quantum dot. The optimum condition for the desired band alignment for emitting wavelength 1.55 μm is investigated using band anticrossing model and the model solid theory. The band gap and the band discontinuities of a Ga1-xInxNyAs1-y/GaAs quantum dot on GaAs are computed with the geometrical confinement effect. The binding energy of the exciton, the oscillator strength and its radiative life time for the optimum condition are found taking into account the spatial confinement effect. The effects of geometrical confinement and the nitrogen incorporation on the interband emission energy are brought out. The result shows that the desired band alignment for emitting wavelength 1.55 μm is achieved for the inclusion of alloy contents, y=0.0554% and x=0.339% in Ga1-xInxNyAs1-y/GaAs quantum dot. And the incorporation of nitrogen and indium shows the red-shift and the geometrical confinement shows the blue-shift. And it can be applied for fibre optical communication networks.

Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates

Energy Technology Data Exchange (ETDEWEB)

Yablonsky, A. N., E-mail: yablonsk@ipm.sci-nnov.ru; Morozov, S. V.; Gaponova, D. M.; Aleshkin, V. Ya. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Shengurov, V. G.; Zvonkov, B. N.; Vikhrova, O. V.; Baidus’, N. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Krasil’nik, Z. F. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2016-11-15

We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.

Plasma treatment of porous GaAs surface formed by electrochemical etching method: Characterization and properties

International Nuclear Information System (INIS)

Naddaf, M.; Saloum, S.

2008-12-01

Porous GaAs samples were formed by electrochemical anodic etching of Zn doped p-type GaAs (100) wafers at different etching parameters (time, mode of applied voltage or current and electrolyte). The effect of etching parameters and plasma surface treatment on the optical properties of the prepared sample has been investigated by using room temperature photoluminescence (PL), Raman spectroscopy and reflectance spectroscopic measurements in the range (400-800 nm). The surface morphological changes were studied by using atomic force microscope. It has been found that etching parameters can be controlled to produce a considerably low optical reflectivity porous GaAs layer, attractive for use in solar cells. In addition, it has been observed that the deposition of plasma polymerized HMDSO thin film on porous GaAs surface can be utilized to produce a surface with novel optical properties interesting for solar cells and optoelectronic devices. (author)

Imaging with Mass Spectrometry: A SIMS and VUV-Photoionization Study of Ion-Sputtered Atoms and Clusters from GaAs and Au

Energy Technology Data Exchange (ETDEWEB)

Takahashi, Lynelle; Zhou, Jia; Wilson, Kevin R.; Leone, Stephen R.; Ahmed, Musahid

2008-12-05

A new mass spectrometry surface imaging method is presented in which ion-sputtered neutrals are postionized by wavelength-tunable vacuum ultraviolet (VUV) light from a synchrotron source. Mass spectra and signal counts of the photoionized neutrals from GaAs (100) and Au are compared to those of the secondary ions. While clusters larger than dimers are more efficiently detected as secondary ions, certain species, such as As2, Au and Au2, are more efficiently detected through the neutral channel. Continuously tuning the photon wavelength allows photoionization efficiency (PIE) curves to be obtained for sputtered Asm (m=1,2) and Aun (n=1-4). From the observed ionization thresholds, sputtered neutral As and Au show no clear evidence of electronic excitation, while neutral clusters have photoionization onsets shifted to lower energies by ~;;0.3 eV. These shifts are attributed to unresolved vibrational and rotational excitations. High-spatial resolution chemical imaging with synchrotron VUV postionization is demonstrated at two different photon energies using a copper TEM grid embedded in indium. The resulting images are used to illustrate the use of tunable VUV light for verifying mass peak assignments by exploiting the unique wavelength-dependent PIE of each sputtered neutral species. This capability is valuable for identifying compounds when imaging chemically complex systems with mass spectrometry-based techniques.

Analysis of GAA/TTC DNA triplexes using nuclear magnetic resonance and electrospray ionization mass spectrometry.

Science.gov (United States)

Mariappan, S V Santhana; Cheng, Xun; van Breemen, Richard B; Silks, Louis A; Gupta, Goutam

2004-11-15

The formation of a GAA/TTC DNA triplex has been implicated in Friedreich's ataxia. The destabilization of GAA/TTC DNA triplexes either by pH or by binding to appropriate ligands was analyzed by nuclear magnetic resonance (NMR) and positive-ion electrospray mass spectrometry. The triplexes and duplexes were identified by changes in the NMR chemical shifts of H8, H1, H4, 15N7, and 15N4. The lowest pH at which the duplex is detectable depends upon the overall stability and the relative number of Hoogsteen C composite function G to T composite function A basepairs. A melting pH (pHm) of 7.6 was observed for the destabilization of the (GAA)2T4(TTC)2T4(CTT)2 triplex to the corresponding Watson-Crick duplex and the T4(CTT)2 overhang. The mass spectrometric analyses of (TTC)6.(GAA)6 composite function(TTC)6 triplex detected ions due to both triplex and single-stranded oligonucleotides under acidic conditions. The triplex ions disappeared completely at alkaline pH. Duplex and single strands were detectable only at neutral and alkaline pH values. Mass spectrometric analyses also showed that minor groove-binding ligands berenil, netropsin, and distamycin and the intercalating ligand acridine orange destabilize the (TTC)6.(GAA)6 composite function (TTC)6 triplex. These NMR and mass spectrometric methods may function as screening assays for the discovery of agents that destabilize GAA/TTC triplexes and as general methods for the characterization of structure, dynamics, and stability of DNA and DNA-ligand complexes.

Structural and morphological TEM characterization of GaAs based nanowires

Energy Technology Data Exchange (ETDEWEB)

Soda, Marcello

2012-02-03

The question of a structural and morphological characterization of GaAs based nanowires is the research interest of this thesis. For this purpose standard and analytical transmission electron microscopy techniques were employed. New investigation methodologies are introduced in order to obtain a reliable interpretation of the results. The principal motivation on developing a new investigation method is the necessity to relate the results of crystal structure and morphology characterizations to microscopic and NW-specific parameters and not to macroscopic and general growth parameters. This allows a reliable comparison of NW characteristics and enhances the comprehension of their growth mechanism.The analysis of the results on crystal structure investigations, assuming this new perspective, delivers the fundamental finding that the axial growth of Au-assisted GaAs NWs can change in a pseudo Ga-assisted growth due to a non steady-state regime of the Ga accumulation process in the liquid droplet. The attempt to associate the observed crystal structures to one of these two growth modes reveals that zinc blende segments are most probably generated when a pseudo Ga-assisted growth occurs. This experimental evidence is in accordance with investigations developed by Glas et al. and Spirkoska et al. and with the current understanding of the NW growth mechanism and unifies the interpretation of catalytic growth of GaAs NWs. A Mn doped GaAs shell deposited at low temperature on core GaAs NWs is characterized for the first time. The growth is found to be epitaxial and to confer the quality of the core crystal to the shell crystal. As a consequence a high stacking fault density of the core NW limits the temperature of the shell growth due to the formation of clusters. Cross sections of (Ga,Mn)As shells are investigated. Simple kinetic and thermodynamical considerations lead to the conclusion of morphological instability of the low temperature radial growth. Analytical

Scattering by nonspherical particles of size comparable to wavelength - A new semi-empirical theory and its application to tropospheric aerosols

Science.gov (United States)

Pollack, J. B.; Cuzzi, J. N.

1980-01-01

A semiempirical theory is developed which is based on simple physical principles and comparisons with laboratory measurements. The ultimate utility of this approach rests on its ability to successfully reproduce the observed single-scattering phase function for a wide variety of particle shapes, sizes and refractive indices. This approximate theory is developed for evaluating the interaction of randomly oriented, nonspherical particles with the total intensity component of electromagnetic radiation. Mie theory is used when the particle size parameter x (ratio of particle circumference to wavelength) is less than some upper bound x sub zero (about 5). For x greater than x sub zero, the interaction is divided into three components: diffraction, external reflection and transmission. The application of the theory is illustrated by considering the influence of the shape of tropospheric aerosols on their contribution to the earth's global albedo.

Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

Science.gov (United States)

Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

1987-01-01

Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

Sulfur passivation of semi-insulating GaAs: Transition from Coulomb blockade to weak localization regime

Energy Technology Data Exchange (ETDEWEB)

Bagraev, N. T., E-mail: Bagraev@mail.ioffe.ru [Ioffe Institute (Russian Federation); Chaikina, E. I. [Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Division de Fisica Aplicada (Mexico); Danilovskii, E. Yu.; Gets, D. S.; Klyachkin, L. E.; L’vova, T. V.; Malyarenko, A. M. [Ioffe Institute (Russian Federation)

2016-04-15

The sulfur passivation of the semi-insulating GaAs bulk (SI GaAs) grown in an excess phase of arsenic is used to observe the transition from the Coulomb blockade to the weak localization regime at room temperature. The I–V characteristics of the SI GaAs device reveal nonlinear behavior that appears to be evidence of the Coulomb blockade process as well as the Coulomb oscillations. The sulfur passivation of the SI GaAs device surface results in enormous transformation of the I–V characteristics that demonstrate the strong increase of the resistance and Coulomb blockade regime is replaced by the electron tunneling processes. The results obtained are analyzed within frameworks of disordering SI GaAs surface that is caused by inhomogeneous distribution of the donor and acceptor anti-site defects which affects the conditions of quantum- mechanical tunneling. Weak localization processes caused by the preservation of the Fermi level pinning are demonstrated by measuring the negative magnetoresistance in weak magnetic fields at room temperature. Finally, the studies of the magnetoresistance at higher magnetic fields reveal the h/2e Aharonov–Altshuler–Spivak oscillations with the complicated behavior due to possible statistical mismatch of the interference paths in the presence of different microdefects.

Characterization of a Ga-assisted GaAs nanowire array solar cell on si substrate

DEFF Research Database (Denmark)

Boulanger, J. P.; Chia, A. C. E.; Wood, B.

2016-01-01

A single-junction core-shell GaAs nanowire (NW) solar cell on Si (1 1 1) substrates is presented. A Ga-assisted vapor–liquid–solid growth mechanism was used for the formation of a patterned array of radial p-i-n GaAs NWs encapsulated in AlInP passivation. Novel device fabrication utilizing facet-...

Nano-dot and nano-pit fabrication on a GaAs substrate by a pulse applied AFM

International Nuclear Information System (INIS)

Kim, H C; Yu, J S; Ryu, S H

2012-01-01

The nano-patterning characteristics of GaAs is investigated using a pulse applied atomic force microscope (AFM). Very short range voltage pulses of micro to nano-seconds’ duration are applied to a conductive diamond-coated silicon (Si) tip in contact mode, to regulate the created feature size. The effects of pulse conditions such as pulse voltage, duration, frequency, offset voltage, anodization time, and applied tip pressure on nano-dot generation are characterized, based on the experiments. An interesting phenomenon, nano-pit creation instead of nano-dot creation, is observed when the applied pulse duration is less than 100 μs. Pulse frequency and offset voltage are also involved in nano-pit generation. The electrical spark discharge between the tip and the GaAs's surface is the most probable cause of the nano-pit creation and its generation mechanism is explained by considering the relevant pulse parameters. Nano-pits over 15 nm in depth are acquired on the GaAs substrate by adjusting the pulse conditions. This research facilitates the fabrication of more complex nano-structures on semiconductor materials since nano-dots and nano-pits could be easily made without any additional post-processes. (paper)

Radiation-induced effects in GaAs thin-film optical (10.6 μm) waveguides

International Nuclear Information System (INIS)

Share, S.; Epstein, A.S.; Monse, T.; Chang, W.S.C.; Chang, M.S.

1976-01-01

Two types of GaAs thin-film optical waveguide structures operating at 10.6 μm were examined before and after exposure to neutron and γ irradiation. The attenuation rate of the GaAs/n + -GaAs structure was particularly sensitive to neutron irradiation of 10 13 cm -2 and exhibited postirradiation annealing at 150 0 C. This is in contrast to the relative neutron irradiation insensitivity of a GaAs/GaAs 1 /sub -//subx/P/subx//n + -GaAs structure. The effect of γ radiation is less pronounced for both structures. The radiation-induced changes are discussed in terms of free-carrier absorption, index of refraction, scattering centers, and absorption by complexes

On-chip microparticle detection and sizing using a dual-wavelength waveguide laser

NARCIS (Netherlands)

Bernhardi, Edward; van der Werf, Kees; Hollink, Anton; Worhoff, Kerstin; de Ridder, R.M.; Subramaniam, Vinod; Pollnau, Markus

An integrated intra-laser-cavity microparticle sensor based on a dual-phase-shift, dual-wavelength distributed-feedback channel waveguide laser in ytterbium-doped aluminium oxide is presented. Single micro-particles with diameters ranging between 1 μm and 20 μm are detected.

Heat load of a GaAs photocathode in an SRF electron gun

International Nuclear Information System (INIS)

Wang Erdong; Zhao Kui; Jorg Kewisch; Ilan Ben-Zvi; Andrew Burrill; Trivini Rao; Wu Qiong; Animesh Jain; Ramesh Gupta; Doug Holmes

2011-01-01

A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved by using a superconducting radio frequency (SRF) electron gun, which delivers beams of a higher brightness than that from DC guns because the field gradient at the cathode is higher. SRF guns with metal and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since a bulk gallium arsenide (GaAs) photocathode is normal conducting, a problem arises from the heat load stemming from the cathode. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and verification by measuring the quality factor of the gun with and without the cathode at 2 K. We simulate heat generation and flow from the GaAs cathode using the ANSYS program. By following the findings with the heat load model, we designed and fabricated a new cathode holder (plug) to decrease the heat load from GaAs. (authors)

Growth-interruption-induced low-density InAs quantum dots on GaAs

International Nuclear Information System (INIS)

Li, L. H.; Alloing, B.; Chauvin, N.; Fiore, A.; Patriarche, G.

2008-01-01

We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/μm 2 ) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 μm emission at 4 K

Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease

Directory of Open Access Journals (Sweden)

Erik van der Wal

2017-06-01

Full Text Available The most common variant causing Pompe disease is c.-32-13T>G (IVS1 in the acid α-glucosidase (GAA gene, which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype. We hypothesized that cis-acting splicing motifs may exist that could be blocked using antisense oligonucleotides (AONs to promote exon inclusion. To test this, a screen was performed in patient-derived primary fibroblasts using a tiling array of U7 small nuclear RNA (snRNA-based AONs. This resulted in the identification of a splicing regulatory element in GAA intron 1. We designed phosphorodiamidate morpholino oligomer-based AONs to this element, and these promoted exon 2 inclusion and enhanced GAA enzyme activity to levels above the disease threshold. These results indicate that the common IVS1 GAA splicing variant in Pompe disease is subject to negative regulation, and inhibition of a splicing regulatory element using AONs is able to restore canonical GAA splicing and endogenous GAA enzyme activity.

Charge collection efficiency in SI GaAs grown from melts with variable composition as a material for solar neutrino detection

CERN Document Server

Verbitskaya, E; Ivanov, A; Strokan, N; Vasilev, V; Markov, A; Polyakov, A; Gavrin, V; Kozlova, Y; Veretenkin, E; Bowles, T J

2000-01-01

The results on electrical characteristics and charge collection efficiency in the detectors from bulk SI GaAs developed as a material for solar neutrino spectroscopy are presented. SI GaAs crystals were grown by the Czochralski method. The changes in the stoichiometric components are permanently controlled. It is shown that the performance of GaAs p sup + -i-n sup + structures provided the range of operational reverse voltage up to 1 kV. Measurement of deep level spectra and their analysis reveal the dominant deep levels - hole traps E sub v +0.51 and +0.075 eV in GaAs grown from stoichiometric and nonstoichiometric melts, respectively. Investigation of carrier transport properties and bulk homogeneity evinced in charge collection efficiency has shown advantageous results for SI GaAs grown from stoichiometric melt. The reduction of carrier transport parameters and charge collection efficiency in GaAs grown from nonstoichiometric melt is analyzed taking into consideration formation of the hole trap E sub v +0....

Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

International Nuclear Information System (INIS)

Li Yanbo; Zhang Yang; Zhang Yuwei; Wang Baoqiang; Zhu Zhanping; Zeng Yiping

2012-01-01

We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (Ga Sb ) defect.

X-ray characterisation of single GaAs nanorods grown on Si

Energy Technology Data Exchange (ETDEWEB)

Biermanns, Andreas; Davydok, A.; Pietsch, Ullrich [Universitaet Siegen (Germany). Festkoerperphysik; Breuer, Steffen; Geelhaar, Lutz [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

2010-07-01

Semiconductor nanorods are of particular interest for new semiconductor devices. The nanorod approach can be used to form radial or axial heterostructures of materials with a large lattice mismatch. For the inspection of average structural parameters of the nanorods, typically X-ray or electron diffraction techniques are used. Alternatively, transmission electron microscopy can be used to inspect few individual nanorods after respective sample preparation. Complementary, recent developments in X-ray optics allow to focus a synchrotron beam down to the nanometer scale and to perform nondestructive diffraction studies at several individual nano-objects grown the same substrate. In this contribution we report on X-ray diffraction studies at individual GaAs nanorods grown Au seed-free on a Si[111] substrate. Due to the nanometer-sized x-ray beam, size and lattice parameters of individual nanorods could be measured and compared to the value obtained from the whole ensemble. Using the coherence properties of the focused beam we could observe speckle-like interference fringes in the surrounding of particular sensitive Bragg reflections which are a measure for the appearance of stacking faults within the nanorods. The separation of the speckles could be used to estimate the number of stacking faults and the size of the coherently scattering nanorod-segments.

GaAs nanowire array solar cells with axial p-i-n junctions.

Science.gov (United States)

Yao, Maoqing; Huang, Ningfeng; Cong, Sen; Chi, Chun-Yung; Seyedi, M Ashkan; Lin, Yen-Ting; Cao, Yu; Povinelli, Michelle L; Dapkus, P Daniel; Zhou, Chongwu

2014-06-11

Because of unique structural, optical, and electrical properties, solar cells based on semiconductor nanowires are a rapidly evolving scientific enterprise. Various approaches employing III-V nanowires have emerged, among which GaAs, especially, is under intense research and development. Most reported GaAs nanowire solar cells form p-n junctions in the radial direction; however, nanowires using axial junction may enable the attainment of high open circuit voltage (Voc) and integration into multijunction solar cells. Here, we report GaAs nanowire solar cells with axial p-i-n junctions that achieve 7.58% efficiency. Simulations show that axial junctions are more tolerant to doping variation than radial junctions and lead to higher Voc under certain conditions. We further study the effect of wire diameter and junction depth using electrical characterization and cathodoluminescence. The results show that large diameter and shallow junctions are essential for a high extraction efficiency. Our approach opens up great opportunity for future low-cost, high-efficiency photovoltaics.

Direct Growth of High-Quality InP Layers on GaAs Substrates by MOCVD

Directory of Open Access Journals (Sweden)

K. F. Yarn

2003-01-01

group V partial pressure, growth rate and V/III ratios. A mirror-like, uniform surface and high crystal quality of the metamorphic buffer layer directly grown on a GaAs substrate can be achieved. Finally, to investigate the performance of the metamorphic microwave devices, we also fabricate the InAlAs/InGaAs metamorphic HEMT on GaAs substrates.

An ultra-high-speed direct digital frequency synthesizer implemented in GaAs HBT technology

International Nuclear Information System (INIS)

Chen Gaopeng; Wu Danyu; Jin Zhi; Liu Xinyu

2010-01-01

This paper presents a 10-GHz 8-bit direct digital synthesizer (DDS) microwave monolithic integrated circuit implemented in 1 μm GaAs HBT technology. The DDS takes a double-edge-trigger (DET) 8-stage pipeline accumulator with sine-weighted DAC-based ROM-less architecture, which can maximize the utilization ratio of the GaAs HBT's high-speed potential. With an output frequency up to 5 GHz, the DDS gives an average spurious free dynamic range of 23.24 dBc through the first Nyquist band, and consumes 2.4 W of DC power from a single -4.6 V DC supply. Using 1651 GaAs HBT transistors, the total area of the DDS chip is 2.4 x 2.0 mm 2 . (semiconductor integrated circuits)

Invariant-based inverse engineering for fluctuation transfer between membranes in an optomechanical cavity system

Science.gov (United States)

Chen, Ye-Hong; Shi, Zhi-Cheng; Song, Jie; Xia, Yan

2018-02-01

In this paper, by invariant-based inverse engineering, we design classical driving fields to transfer quantum fluctuations between two suspended membranes in an optomechanical cavity system. The transfer can be quickly attained through a nonadiabatic evolution path determined by a so-called dynamical invariant. Such an evolution path allows one to optimize the occupancies of the unstable "intermediate" states; thus, the influence of cavity decays can be suppressed. Numerical simulation demonstrates that a perfect fluctuation transfer between two membranes can be rapidly achieved in one step, and the transfer is robust to both the amplitude noises and cavity decays.

X-ray in-situ study of copper electrodeposition on UHV prepared GaAs(001) surfaces

Energy Technology Data Exchange (ETDEWEB)

Gruender, Yvonne

2008-06-02

For this work a unique setup for in-situ electrochemical studies was employed and improved. This setup permits UHV preparation of the GaAs(001) surface with a defined surface termination (arsenic-rich or gallium-rich) and its characterization by SXRD in UHV, under ambient pressure in inert gas and in electrolyte under potential control without passing through air. The GaAs(001) surfaces were capped by amorphous arsenic. This permitted to ship them through ambient air. Afterwards smooth well defined GaAs(001) surfaces could be recovered by thermal annealing in UHV. A first investigation of the arsenic capped sample was done by atomic force microscopy (AFM) and Surface X-Ray Diffraction (SXRD). The non bulk like termination of the arsenic buried GaAs(001) surface was revealed. For the electrochemical metal deposition, arsenic terminated (2 x 4) reconstructed and gallium terminated (4 x 2) reconstructed GaAs(001) surfaces were employed. These surfaces were characterized by STM, LEED and a first time by SXRD. The surfaces are smooth, however, a higher degree of disorder than for MBE prepared reconstructed GaAs(001) is found. After exposure of the sample to nitrogen, the surfaces were then again studied by SXRD. These two steps characterizing the bare GaAs(001) surfaces permitted us to get a better knowledge of the starting surface and its influence on the later electrodeposited copper. At ambient pressure both reconstructions are lifted, but the surface is not bulk-like terminated as can be deduced from the crystal truncation rods. Epitaxial copper clusters grow upon electrodeposition on the UHV prepared GaAs(001) surface. The copper lattice is rotated and inclined with respect to the GaAs substrate lattice, leading to eight symmetry equivalent domains. The influence of the surface termination as well as the nucleation potential on the structure of the electrodeposited copper were investigated. The tilt and rotation angles do not depend on the deposition potential but

Cavity optomechanics in a levitated helium drop

Science.gov (United States)

Childress, L.; Schmidt, M. P.; Kashkanova, A. D.; Brown, C. D.; Harris, G. I.; Aiello, A.; Marquardt, F.; Harris, J. G. E.

2017-12-01

We describe a proposal for a type of optomechanical system based on a drop of liquid helium that is magnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whispering-gallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mm-scale and cm-scale drops of liquid He , evaporative cooling of He droplets in vacuum, and coupling to high-quality optical whispering-gallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the single-photon strong-coupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of 4He). Alternatively, for a normal fluid drop of 3He, we propose to exploit the coupling between the drop's rotations and vibrations to perform quantum nondemolition measurements of angular momentum.

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

Science.gov (United States)

Louarn, K.; Claveau, Y.; Marigo-Lombart, L.; Fontaine, C.; Arnoult, A.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

2018-04-01

In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm‑2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

Quantum synchronization in an optomechanical system based on Lyapunov control.

Science.gov (United States)

Li, Wenlin; Li, Chong; Song, Heshan

2016-06-01

We extend the concepts of quantum complete synchronization and phase synchronization, which were proposed in A. Mari et al., Phys. Rev. Lett. 111, 103605 (2013)PRLTAO0031-900710.1103/PhysRevLett.111.103605, to more widespread quantum generalized synchronization. Generalized synchronization can be considered a necessary condition or a more flexible derivative of complete synchronization, and its criterion and synchronization measure are proposed and analyzed in this paper. As examples, we consider two typical generalized synchronizations in a designed optomechanical system. Unlike the effort to construct a special coupling synchronization system, we purposefully design extra control fields based on Lyapunov control theory. We find that the Lyapunov function can adapt to more flexible control objectives, which is more suitable for generalized synchronization control, and the control fields can be achieved simply with a time-variant voltage. Finally, the existence of quantum entanglement in different generalized synchronizations is also discussed.

GaAs photovoltaics and optoelectronics using releasable multilayer epitaxial assemblies.

Science.gov (United States)

Yoon, Jongseung; Jo, Sungjin; Chun, Ik Su; Jung, Inhwa; Kim, Hoon-Sik; Meitl, Matthew; Menard, Etienne; Li, Xiuling; Coleman, James J; Paik, Ungyu; Rogers, John A

2010-05-20

Compound semiconductors like gallium arsenide (GaAs) provide advantages over silicon for many applications, owing to their direct bandgaps and high electron mobilities. Examples range from efficient photovoltaic devices to radio-frequency electronics and most forms of optoelectronics. However, growing large, high quality wafers of these materials, and intimately integrating them on silicon or amorphous substrates (such as glass or plastic) is expensive, which restricts their use. Here we describe materials and fabrication concepts that address many of these challenges, through the use of films of GaAs or AlGaAs grown in thick, multilayer epitaxial assemblies, then separated from each other and distributed on foreign substrates by printing. This method yields large quantities of high quality semiconductor material capable of device integration in large area formats, in a manner that also allows the wafer to be reused for additional growths. We demonstrate some capabilities of this approach with three different applications: GaAs-based metal semiconductor field effect transistors and logic gates on plates of glass, near-infrared imaging devices on wafers of silicon, and photovoltaic modules on sheets of plastic. These results illustrate the implementation of compound semiconductors such as GaAs in applications whose cost structures, formats, area coverages or modes of use are incompatible with conventional growth or integration strategies.

Surface chemistry and growth mechanisms studies of homo epitaxial (1 0 0) GaAs by laser molecular beam epitaxy

International Nuclear Information System (INIS)

Yan Dawei; Wu Weidong; Zhang Hong; Wang Xuemin; Zhang Hongliang; Zhang Weibin; Xiong Zhengwei; Wang Yuying; Shen Changle; Peng Liping; Han Shangjun; Zhou Minjie

2011-01-01

In this paper, GaAs thin film has been deposited on thermally desorbed (1 0 0) GaAs substrate using laser molecular beam epitaxy. Scanning electron microscopy, in situ reflection high energy electron diffraction and in situ X-ray photoelectron spectroscopy are applied for evaluation of the surface morphology and chemistry during growth process. The results show that a high density of pits is formed on the surface of GaAs substrate after thermal treatment and the epitaxial thin film heals itself by a step flow growth, resulting in a smoother surface morphology. Moreover, it is found that the incorporation of As species into GaAs epilayer is more efficient in laser molecular beam epitaxy than conventional molecular beam epitaxy. We suggest the growth process is impacted by surface chemistry and morphology of GaAs substrate after thermal treatment and the growth mechanisms are discussed in details.

A two-wavelength imaging pyrometer for measuring particle temperature, velocity and size in thermal spray processes

International Nuclear Information System (INIS)

Craig, J.E.; Parker, R.A.; Lee, D.Y.; Biancaniello, F.; Ridder, S.

1999-01-01

An imaging pyrometer has been developed to measure the surface temperature of hot metal objects and to measure particle temperature, velocity and size in thermal spray, spray-fonning and atomization processes. The two-wavelength surface imaging pyrometer provides true temperature measurement with high resolution, even when the surface has emissivity variation caused by roughness or oxidation. The surface imaging pyrometer has been calibrated for use in a material processing lab calibration over the range of 1000 to 3000 deg K, and these results are described. The particle imaging pyrometer has a field of view that spans the entire particle stream in typical thermal spray devices, and provides continuous measurement of the entire particle stream. Particle temperature and velocity are critical parameters for producing high quality spray coatings efficiently and reliably. The software locates the particle streaks in the image, and determines the intensity ratio for each particle streak pair to obtain the temperature. The dimensions of the particle streak image are measured to determine the velocity and size. Because the vision-based sensor samples the entire particle stream in every video frame, the particle temperature, velocity and size data are updated at 30 Hz at all points in the particle stream. Particle measurements in a plasma spray at NIST are described. In this paper, we will describe our experiments with ceramic powders, in which measurements have been made at several positions along the particle stream. The particle data are represented as profiles across the particle stream, histograms of the full particle stream or time histories of the full-stream average. The results are compared and calibrated with other temperature and diagnostic measurement systems. (author)

Picosecond relaxation of X-ray excited GaAs

Czech Academy of Sciences Publication Activity Database

Tkachenko, V.; Medvedev, Nikita; Lipp, V.; Ziaja, B.

2017-01-01

Roč. 24, Sep (2017), s. 15-21 ISSN 1574-1818 Institutional support: RVO:68378271 Keywords : GaAS * X-ray excitation * picosecond relaxation Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 0.908, year: 2016

Base excision repair of chemotherapeutically-induced alkylated DNA damage predominantly causes contractions of expanded GAA repeats associated with Friedreich's ataxia.

Directory of Open Access Journals (Sweden)

Yanhao Lai

Full Text Available Expansion of GAA·TTC repeats within the first intron of the frataxin gene is the cause of Friedreich's ataxia (FRDA, an autosomal recessive neurodegenerative disorder. However, no effective treatment for the disease has been developed as yet. In this study, we explored a possibility of shortening expanded GAA repeats associated with FRDA through chemotherapeutically-induced DNA base lesions and subsequent base excision repair (BER. We provide the first evidence that alkylated DNA damage induced by temozolomide, a chemotherapeutic DNA damaging agent can induce massive GAA repeat contractions/deletions, but only limited expansions in FRDA patient lymphoblasts. We showed that temozolomide-induced GAA repeat instability was mediated by BER. Further characterization of BER of an abasic site in the context of (GAA20 repeats indicates that the lesion mainly resulted in a large deletion of 8 repeats along with small expansions. This was because temozolomide-induced single-stranded breaks initially led to DNA slippage and the formation of a small GAA repeat loop in the upstream region of the damaged strand and a small TTC loop on the template strand. This allowed limited pol β DNA synthesis and the formation of a short 5'-GAA repeat flap that was cleaved by FEN1, thereby leading to small repeat expansions. At a later stage of BER, the small template loop expanded into a large template loop that resulted in the formation of a long 5'-GAA repeat flap. Pol β then performed limited DNA synthesis to bypass the loop, and FEN1 removed the long repeat flap ultimately causing a large repeat deletion. Our study indicates that chemotherapeutically-induced alkylated DNA damage can induce large contractions/deletions of expanded GAA repeats through BER in FRDA patient cells. This further suggests the potential of developing chemotherapeutic alkylating agents to shorten expanded GAA repeats for treatment of FRDA.

Charge collection efficiency in SI GaAs grown from melts with variable composition as a material for solar neutrino detection

International Nuclear Information System (INIS)

Verbitskaya, E.; Eremin, V.; Ivanov, A.; Strokan, N.; Vasilev, V.; Markov, A.; Polyakov, A.; Gavrin, V.; Kozlova, Yu.; Veretenkin, E.; Bowles, T.J.

2000-01-01

The results on electrical characteristics and charge collection efficiency in the detectors from bulk SI GaAs developed as a material for solar neutrino spectroscopy are presented. SI GaAs crystals were grown by the Czochralski method. The changes in the stoichiometric components are permanently controlled. It is shown that the performance of GaAs p + -i-n + structures provided the range of operational reverse voltage up to 1 kV. Measurement of deep level spectra and their analysis reveal the dominant deep levels - hole traps E v +0.51 and +0.075 eV in GaAs grown from stoichiometric and nonstoichiometric melts, respectively. Investigation of carrier transport properties and bulk homogeneity evinced in charge collection efficiency has shown advantageous results for SI GaAs grown from stoichiometric melt. The reduction of carrier transport parameters and charge collection efficiency in GaAs grown from nonstoichiometric melt is analyzed taking into consideration formation of the hole trap E v +0.075 eV, presumably assigned to Ga antisite and its influence on the concentration of the ionized deep donor level EL2 +

Subnanosecond, high-voltage photoconductive switching in GaAs

Science.gov (United States)

Druce, Robert L.; Pocha, Michael D.; Griffin, Kenneth L.; O'Bannon, Jim

1991-03-01

We are conducting research on the switching properties of photoconductive materials to explore their potential for generating highpower microwaves (HPM) and for high reprate switching. We have investigated the performance of Gallium Arsenide (GaAs) in linear mode (the conductivity of the device follows the optical pulse) as well as an avalanchelike mode (the optical pulse only controls switch closing) . Operating in the unear mode we have observed switch closing times of less than 200 Ps with a 100 ps duration laser pulse and opening times of less than 400 ps at several kV/cm fields using neutron irradiated GaAs. In avalanche and lockon modes high fields are switched with lower laser pulse energies resulting in higher efficiencies but with measurable switching delay and jitter. We are currently investigating both large area (1 cm2) and small area 1 mm2) switches illuminated by AlGaAs laser diodes at 900 nm and Nd:YAG lasers at 1. 06 tim.

Sn nanothreads in GaAs: experiment and simulation

Science.gov (United States)

Semenikhin, I.; Vyurkov, V.; Bugaev, A.; Khabibullin, R.; Ponomarev, D.; Yachmenev, A.; Maltsev, P.; Ryzhii, M.; Otsuji, T.; Ryzhii, V.

2016-12-01

The gated GaAs structures like the field-effect transistor with the array of the Sn nanothreads was fabricated via delta-doping of vicinal GaAs surface by Sn atoms with a subsequent regrowth. That results in the formation of the chains of Sn atoms at the terrace edges. Two device models were developed. The quantum model accounts for the quantization of the electron energy spectrum in the self-consistent two-dimensional electric potential, herewith the electron density distribution in nanothread arrays for different gate voltages is calculated. The classical model ignores the quantization and electrons are distributed in space according to 3D density of states and Fermi-Dirac statistics. It turned out that qualitatively both models demonstrate similar behavior, nevertheless, the classical one is in better quantitative agreement with experimental data. Plausibly, the quantization could be ignored because Sn atoms are randomly placed along the thread axis. The terahertz hot-electron bolometers (HEBs) could be based on the structure under consideration.

Scattering by non-spherical particles of size comparable to a wavelength - A new semi-empirical theory. [atmospheric radiative transfer

Science.gov (United States)

Pollack, J. B.; Cuzzi, J. N.

1978-01-01

Mie theory, which is generally used to describe the scattering behavior of particles at a certain wavelength, is only rigorously correct for spherical particles. Particles found as atmospheric constituents, with the exception of cloud droplets, are, however, decidedly nonspherical. An investigation is, therefore, conducted regarding the significant ways in which the scattering behavior of irregularly shaped particles differs from that of spheres. A systematic method is formulated for treating the real scalar scattering behavior. A description is presented of a new semiempirical theory based on simple physical principles and data obtained in laboratory measurements, which successfully reproduces the single scattering phase function for a wide range of particle shapes, sizes, and refractive indices.

Modeling the effect of deep impurity ionization on GaAs photoconductive switches

Energy Technology Data Exchange (ETDEWEB)

Yee, J.H.; Khanaka, G.H.; Druce, R.L.; Pocha, M.D.

1992-01-01

The ionization coefficient of deep traps in GaAs is determined from a gas breakdown model together with the recent experimental data obtained at LLNL (Lawrence Livermore National Laboratory) and Boeing. Using this coefficient in our nonlinear device transport code, we have investigated theoretically the nonlinear switching phenomena in GaAs devices. The results obtained from our investigations show that if we take into consideration the effect of the field ionization of the deep traps, we can show how the Lock-On'' phenomena could occur in the device.

Modeling the effect of deep impurity ionization on GaAs photoconductive switches

Energy Technology Data Exchange (ETDEWEB)

Yee, J.H.; Khanaka, G.H.; Druce, R.L.; Pocha, M.D.

1992-01-01

The ionization coefficient of deep traps in GaAs is determined from a gas breakdown model together with the recent experimental data obtained at LLNL (Lawrence Livermore National Laboratory) and Boeing. Using this coefficient in our nonlinear device transport code, we have investigated theoretically the nonlinear switching phenomena in GaAs devices. The results obtained from our investigations show that if we take into consideration the effect of the field ionization of the deep traps, we can show how the ``Lock-On`` phenomena could occur in the device.

GaAs thin film solar cells. Final report; Duennschicht-Solarzellen aus Galliumarsenid; Abschlussbericht

Energy Technology Data Exchange (ETDEWEB)

Bett, A.; Bronner, W.; Cardona, S.; Ehrhardt, A.; Habermann, G.; Habich, A.; Lanyi, P.; Lutz, F.; Nguyen, T.; Schetter, C.; Sulima, O.; Welter, H.; Yavas, O.

1992-11-01

This R and D project focused on the development of materials and technologies for the production of GaAs solar cells on GaAs and other substrates. Three subjects were gone into on particular: Material preparation (epitaxy), solar cell technology, characterisation of materials and processes. (orig.) [Deutsch] Das vorliegende Forschungsvorhaben hatte die Material- und Technologieentwickung fuer die Herstellung von GaAs-Solarzellen auf Eigen- und Fremdsubstrat zum Gegenstand. Drei Hauptaufgabenbereiche waren: Materialpraeparation (Epitaxie), Solarzellentechnologie, sowie Material- und Prozesscharakterisierung. (orig.)

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

Science.gov (United States)

Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

2018-05-01

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

Electro-Optomechanical Transduction & Quantum Hard-Sphere Model for Dissipative Rydberg-EIT Media

DEFF Research Database (Denmark)

Zeuthen, Emil

by two key parameters, the signal transfer efficiency and added noise temperature. In terms of these, we may evaluate its performance in various tasks ranging from classical signal detection to quantum state conversion between, e.g., superconducting circuitry and traveling optical signals. Having...... transduction functionality into the well-established framework of electrical engineering, thereby facilitating its implementation in potential applications such as nuclear magnetic resonance imaging and radio astronomy. We consider such optomechanical sensing of weak electrical signals and discuss how...... in a cold, optically dense cloud with light fields propagating under the condition of electromagnetically induced transparency (EIT). This can lead to strong and non-linear dissipative dynamics at the quantum level that prevent slow-light polaritons from coexisting within a blockade radius of one another...

Large tuning of birefringence in two strip silicon waveguides via optomechanical motion.

Science.gov (United States)

Ma, Jing; Povinelli, Michelle L

2009-09-28

We present an optomechanical method to tune phase and group birefringence in parallel silicon strip waveguides. We first calculate the deformation of suspended, parallel strip waveguides due to optical forces. We optimize the frequency and polarization of the pump light to obtain a 9 nm deformation for an optical power of 20 mW. Widely tunable phase and group birefringence can be achieved by varying the pump power, with maximum values of 0.026 and 0.13, respectively. The giant phase birefringence allows linear to circular polarization conversion within 30 microm for a pump power of 67 mW. The group birefringence gives a tunable differential group delay of 6fs between orthogonal polarizations. We also evaluate the tuning performance of waveguides with different cross sections.

Complex laterally ordered InGaAs and InAs quantum dots by guided self-organized anisotropic strain engineering on artificially patterned GaAs (3 1 1)B substrates

NARCIS (Netherlands)

Selçuk, E.; Hamhuis, G.J.; Nötzel, R.

2009-01-01

Self-organized anisotropic strain engineering is combined with growth on artificially patterned GaAs (3 1 1)B substrates to realize complex lateral ordering of InGaAs and InAs quantum dots (QDs) guided by steps and facets generated along the pattern sidewalls. Depending on the pattern design, size,

Removal of NO {sub x} by microwave reactor with ammonium bicarbonate and Ga-A zeolites at low temperature

Energy Technology Data Exchange (ETDEWEB)

Wei, Z.S. [School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275 (China)]. E-mail: weizaishan98@163.com; Du, Z.Y. [School of Light Industry and Chemical Engineering, Guangdong University of Technology, Guangzhou 510006 (China); Lin, Z.H. [School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); He, H.M. [School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Qiu, R.L. [School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275 (China)

2007-08-15

Microwave reactor with the mixture of ammonium bicarbonate (NH{sub 4}HCO{sub 3}) and Ga-A zeolites was set up to study the removal of nitrogen oxides (NO {sub x} ) from waste gas with excess oxygen concentration (14-19%) at low temperature (80-120 deg. C). The results showed that the microwave reactor filled with NH{sub 4}HCO{sub 3} and Ga-A zeolites could reduce NO {sub x} to nitrogen with the best purifying efficiency of 95.45% and the best denitrification amount of 89.28 mg h{sup -1}. The optimal microwave power and residence time (RT) on denitrification was 259-280 W and 0.259 s, respectively. Microwave denitrification effect of the experiment using ammonium bicarbonate and Ga-A zeolites was much higher than that using ammonium bicarbonate or Ga-A zeolites only. The mechanism for microwave-induced NO {sub x} reduction can be explained as the microwave-induced catalytic reaction between NO {sub x} and ammonium bicarbonate with Ga-A zeolites being the catalyst and microwave absorbent.

Shallow Levels Characterization in Epitaxial GaAs by Acousto-Optic Reflectance Shallow Levels Characterization in Epitaxial GaAs by Acousto-Optic Reflectance

Directory of Open Access Journals (Sweden)

O. G. Ibarra-Manzano

2012-02-01

Full Text Available Optical spectra of light reflection are detected under an influence of ultrasonic wave (UWon a GaAs wafer. The differential spectrum is calculated as a difference between those taken under UW and without that influence on a sample. This acousto-optic differential reflectance(AODR spectrum contains some bands that represent the energetic levels of the shallow centers in a sample. A physical basis of this technique is related to a perturbation of local states by UW. Here, a method is developed for characterization of local states at the surfaces and interfaces in crystals and low-dimensional epitaxial structures based on microelectronics materials. A theoretical model is presented to explain AODR spectra. Also, experiments using epitaxial GaAs structures doped by Te were made. Finally, theoretical and experimental results show that acousto-optic reflectance is an effective tool for characterization of shallow trapping centers in epitaxial semiconductor structures.En este trabajo, utilizamos el espectro de la luz reflejada en una muestra de Arsenuro de Galio (GaAs bajo la influencia de una onda ultrasónica. El diferencial espectral es calculado como una diferencia entre el espectro del material obtenido bajo la influencia del ultrasonido y aquél obtenido sin dicha influencia. Este diferencial de reflectancia espectral acusto-óptico (AODR contiene algunas bandas que representan los niveles energéticos de los centros en la superficie de la muestra. Esta técnica está basada en la perturbación de los estados locales generada por el ultrasonido. Particularmente, este trabajo presenta un método para caracterizar los estados locales en la superficie y las interfaces en los cristales, así como estructuras epiteliales de baja dimensión basadas en materiales semiconductores. Para ello, se presenta un modelo teórico para explicar dicho espectro de reflectancia diferencial (AODR. También se realizaron experimentos con estructuras de GaAs epitelial

Phase control of entanglement and quantum steering in a three-mode optomechanical system

Science.gov (United States)

Sun, F. X.; Mao, D.; Dai, Y. T.; Ficek, Z.; He, Q. Y.; Gong, Q. H.

2017-12-01

The theory of phase control of coherence, entanglement and quantum steering is developed for an optomechanical system composed of a single mode cavity containing a partially transmitting dielectric membrane and driven by short laser pulses. The membrane divides the cavity into two mutually coupled optomechanical cavities resulting in an effective three-mode closed loop system, two field modes of the two cavities and a mechanical mode representing the oscillating membrane. The closed loop in the coupling creates interfering channels which depend on the relative phase of the coupling strengths of the field modes to the mechanical mode. Populations and correlations of the output modes are calculated analytically and show several interesting phase dependent effects such as reversible population transfer from one field mode to the other, creation of collective modes, and induced coherence without induced emission. We find that these effects result from perfect mutual coherence between the field modes which is preserved even if one of the modes is not populated. The inseparability criterion for the output modes is also investigated and we find that entanglement may occur only between the field modes and the mechanical mode. We show that depending on the phase, the field modes can act on the mechanical mode collectively or individually resulting, respectively, in tripartite or bipartite entanglement. In addition, we examine the phase sensitivity of quantum steering of the mechanical mode by the field modes. Deterministic phase transfer of the steering from bipartite to collective is predicted and optimum steering corresponding to perfect EPR state can be achieved. These different types of quantum steering can be distinguished experimentally by measuring the coincidence rate between two detectors adjusted to collect photons of the output cavity modes. In particular, we find that the minima of the interference pattern of the coincidence rate signal the bipartite steering

Twins and strain relaxation in zinc-blende GaAs nanowires grown on silicon

Energy Technology Data Exchange (ETDEWEB)

Piñero, J.C., E-mail: josecarlos.pinero@uca.es [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Araújo, D.; Pastore, C.E.; Gutierrez, M. [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Frigeri, C. [Istituto CNR-IMEM Parco Area delle Scienze 37/A, Fontanini, 43010, Parma (Italy); Benali, A.; Lelièvre, J.F.; Gendry, M. [INL-Institut des Nanotechnologies de Lyon, UMR 5270 Ecole Centrale de Lyon 36, Avenue Guy de Collongue, 69134, Ecully Cedex (France)

2017-02-15

Highlights: • A TEM-HREM study of GaAs nanowires, growth over Si, is presented. • Misfit dislocations are detected in the Si/GaAs magma interface. • The study demonstrates strain relaxation through twin formation in some nanowires. - Abstract: To integrate materials with large lattice mismatch as GaAs on silicon (Si) substrate, one possible approach, to improve the GaAs crystalline quality, is to use nanowires (NWs) technology. In the present contribution, NWs are grown on <111> oriented Si substrates by molecular beam epitaxy (MBE) using vapor-liquid-solid (VLS) method. Transmission electron microscopy (TEM) analyses show that NWs are mainly grown alternating wurtzite and zinc blend (ZB) phases, and only few are purely ZB. On the latter, High Resolution Electron Microscopy (HREM) evidences the presence of twins near the surface of the NW showing limited concordance with the calculations of Yuan (2013) [1], where {111} twin planes in a <111>-oriented GaAs NW attain attractive interactions mediated by surface strain. In addition, such twins allow slight strain relaxation and are probably induced by the local huge elastic strain observed by HREM in the lattice between the twin and the surface. The latter is attributed to some slight bending of the NW as shown by the inversion of the strain from one side to the other side of the NW.

Epitaxial growth on porous GaAs substrates

Czech Academy of Sciences Publication Activity Database

Grym, Jan; Nohavica, Dušan; Gladkov, Petar; Hulicius, Eduard; Pangrác, Jiří; Piksová, K.

2013-01-01

Roč. 16, č. 1 (2013), s. 59-64 ISSN 1631-0748 R&D Projects: GA ČR GAP102/10/1201; GA ČR GAP108/10/0253 Institutional support: RVO:67985882 ; RVO:68378271 Keywords : Electrochemical etching * Porous semiconductors * Epitaxial growth * GaAs Subject RIV: BH - Optics, Masers, Lasers; JA - Electronics ; Optoelectronics, Electrical Engineering (FZU-D) Impact factor: 1.483, year: 2013

The lower yield point of InP and GaAs

International Nuclear Information System (INIS)

Siethoff, H.

1987-01-01

A study of the strain-rate and temperature dependence of the lower yield stress (τ ly ) in undoped InP and of the strain-rate dependence of τ ly in undoped and Zn-doped GaAs is reported. The deformation along (123) orientation was carried out in compression at constant strain rates ranging from 10 -5 to 10 -2 s -1 . The temperature range extended from 540 to 780 0 C. The activation energy and stress exponent of the dislocation velocity were calculated. Experiments have shown that τ ly of InP depends on temperature and strain rate in a manner similar to other semiconductors like Si and InSb, whereas τ ly of GaAs shows an unusual strain-rate dependence

Investigations of the physical properties of photoemission polarized electron sources for accelerator applications

International Nuclear Information System (INIS)

Dunham, B.M.

1993-01-01

This experiment measured the polarization and quantum efficiency as a function of wavelength for the chalcopyrite semiconductor Zn (Ge 0.7 Si 0.3 )As 2 . Also, the onset of space charge growth of a 100 keV electron beam passing through the Illinois/CEBAF polarized electron injection system was studied by measuring the beam emittance as a function of current. Finally the thermal properties of GaAs were investigated by measuring the beam emittance as functions of the excitation laser wavelength and the laser spot size. The experiments were performed of Zn(Ge 0.7 Si 0.3 )As 2 was measured to be ∼19%, much lower than the expected 100%. Also, the expected emittance as a function of current was measured and the onset of space charge effects was found to be ∼0.5 mA, much lower than predicted by the electron gun design program EGUN. Finally, the effective transverse thermal energy of the electrons emitted from GaAs at 100 keV as a function of excitation wavelength was measured by a new method for low beam currents. The electron thermal energy for wavelengths between 840 and 633 nm was found to be ∼33 meV, a factor of 3 lower than for a thermionic electron gun. It was found to increase sharply for photon wavelengths less than 633 nm

Improved predictive modeling of white LEDs with accurate luminescence simulation and practical inputs with TracePro opto-mechanical design software

Science.gov (United States)

Tsao, Chao-hsi; Freniere, Edward R.; Smith, Linda

2009-02-01

The use of white LEDs for solid-state lighting to address applications in the automotive, architectural and general illumination markets is just emerging. LEDs promise greater energy efficiency and lower maintenance costs. However, there is a significant amount of design and cost optimization to be done while companies continue to improve semiconductor manufacturing processes and begin to apply more efficient and better color rendering luminescent materials such as phosphor and quantum dot nanomaterials. In the last decade, accurate and predictive opto-mechanical software modeling has enabled adherence to performance, consistency, cost, and aesthetic criteria without the cost and time associated with iterative hardware prototyping. More sophisticated models that include simulation of optical phenomenon, such as luminescence, promise to yield designs that are more predictive - giving design engineers and materials scientists more control over the design process to quickly reach optimum performance, manufacturability, and cost criteria. A design case study is presented where first, a phosphor formulation and excitation source are optimized for a white light. The phosphor formulation, the excitation source and other LED components are optically and mechanically modeled and ray traced. Finally, its performance is analyzed. A blue LED source is characterized by its relative spectral power distribution and angular intensity distribution. YAG:Ce phosphor is characterized by relative absorption, excitation and emission spectra, quantum efficiency and bulk absorption coefficient. Bulk scatter properties are characterized by wavelength dependent scatter coefficients, anisotropy and bulk absorption coefficient.

The role of proximity caps during the annealing of UV-ozone oxidized GaAs

International Nuclear Information System (INIS)

Ghosh, S. C.; Biesinger, M. C.; LaPierre, R. R.; Kruse, P.

2007-01-01

This study provides a deeper insight into the chemistry and physics of the common engineering practice of using a proximity cap, while annealing compound semiconductors such as GaAs. We have studied the cases of a GaAs proximity cap, a Si proximity cap, and no proximity cap. Using x-ray photoelectron spectroscopy, it has been found that annealing increases the gallium to arsenic ratio in the oxide layer in all cases. During the annealing of UV-ozone oxidized GaAs, it has been observed that GaAs proximity caps also serve as a sacrificial layer to accelerate the desorption of oxide species. In all cases surface deterioration due to pit formation has been observed, and the depth of pits is found to depend on the effective role played by the capping material. Energy dispersive x-ray analysis provides additional evidence that pits mainly consist of elemental As and gallium oxide, with most of the elemental As situated at the pit-substrate interface. Deposition of a thin layer of gold and subsequent annealing to 500 deg. C for 300 s under different capping conditions shows the use of a proximate cap to be practically insignificant in annealing Au deposited films

Anisotropic Pauli Spin Blockade of Holes in a GaAs Double Quantum Dot

Science.gov (United States)

Wang, Qingwen; Klochan, Oleh; Hung, Jo-Tzu; Culcer, Dimitrie; Farrer, Ian; Ritchie, David; Hamilton, Alex

Electrically defined semiconductor quantum dots are appealing systems for spin manipulation and quantum information processing. Thanks to the weak hyperfine interaction and the strong spin-orbit interaction, heavy-holes in GaAs are promising candidates for all-electrical spin manipulation. However, making stable quantum dots in GaAs has only become possible recently, mainly because of difficulties in device fabrication and device stability. Here we present electrical transport measurements of heavy-holes in a lateral double quantum dot based on a GaAs /AlxGa1 - x As heterostructure. We observe clear Pauli spin blockade and show that the lifting of the spin blockade by an external magnetic field is extremely anisotropic. Numerical calculations of heavy-hole transport through a double quantum dot in the presence of strong spin-orbit interaction demonstrate quantitative agreement with experimental results, which indicates that the observed anisotropy can be explained by the anisotropic hole g-factor and the surface Dresselhaus spin-orbit coupling.

Performance of Series Connected GaAs Photovoltaic Converters under Multimode Optical Fiber Illumination

Directory of Open Access Journals (Sweden)

Tiqiang Shan

2014-01-01

Full Text Available In many military and industrial applications, GaAs photovoltaic (PV converters are connected in series in order to generate the required voltage compatible with most common electronics. Multimode optical fibers are usually used to carry high-intensity laser and illuminate the series connected GaAs PV converters in real time. However, multimode optical fiber illumination has a speckled intensity pattern. The series connected PV array is extremely sensitive to nonuniform illumination; its performance is limited severely by the converter that is illuminated the least. This paper quantifies the effects of multimode optical fiber illumination on the performance of series connected GaAs PV converters, analyzes the loss mechanisms due to speckles, and discusses the maximum illumination efficiency. In order to describe the illumination dependent behavior detailedly, modeling of the series connected PV array is accomplished based on the equivalent circuit for PV cells. Finally, a series of experiments are carried out to demonstrate the theory analysis.

MIT wavelength tables. Volume 2. Wavelengths by element

International Nuclear Information System (INIS)

Phelps, F.M. III.

1982-01-01

This volume is the first stage of a project to expand and update the MIT wavelength tables first compiled in the 1930's. For 109,325 atomic emission lines, arranged by element, it presents wavelength in air, wavelength in vacuum, wave number and intensity. All data are stored on computer-readable magnetic tape

Optimization of the GaAs et GaAs/Si annealing using halogen lamp flashes

International Nuclear Information System (INIS)

Blanck, H.

1989-01-01

The aim of the work is to check whether the flash annealing of GaAs and GaAs/Si, using halogen lamps, allows an improvement in the results obtained by usual methods. The electrical activation, defects behavior and results uniformity are studied. The results on the activation and diffusion of implanted impurities are shown to be equivalent to those obtained with classical annealing methods. However, residual impurities (or defects) diffusion phenomena are restrained by the flash annealing technique. The Hall effect cartographic measurements showed an improvement of the uniformity of the implanted coating surface resistance. Flash annealing is a suitable method for the Si activation in GaAs. It allows an improvement of the GaAs results obtained with standard techniques, as well as the formation, by means of ion implantation, of active zones in the GaAs/Si layers [fr

P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

Energy Technology Data Exchange (ETDEWEB)

Jin, Y.J.; Chia, C.K.; Liu, H.F.; Wong, L.M.; Chai, J.W.; Chi, D.Z.; Wang, S.J., E-mail: sj-wang@imre.a-star.edu.sg

2016-07-15

Highlights: • The heterogeneous integration of p-Ge/GaAs by MOCVD indicates significance for the application in optoelectronic devices such as p-MOSFET, dual band photodetector, etc. • Many undesired pillar-structures were observed on the p-Ge epilayers and we found that the cause of the pillar-like structures was related to the Ge-Ga dimers formed during the growth. • We found that a GaAs substrate with fewer Ga or Ge danglings was helpful in suppressing the formation of the unwanted pillar-like structures and thus obtaining high quality p-Ge epilayers. - Abstract: In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures.

Modelling of OPNMR phenomena using photon energy-dependent 〈Sz〉 in GaAs and InP

Science.gov (United States)

Wheeler, Dustin D.; Willmering, Matthew M.; Sesti, Erika L.; Pan, Xingyuan; Saha, Dipta; Stanton, Christopher J.; Hayes, Sophia E.

2016-12-01

We have modified the model for optically-pumped NMR (OPNMR) to incorporate a revised expression for the expectation value of the z-projection of the electron spin, 〈Sz 〉 and apply this model to both bulk GaAs and a new material, InP. This expression includes the photon energy dependence of the electron polarization when optically pumping direct-gap semiconductors in excess of the bandgap energy, Eg . Rather than using a fixed value arising from coefficients (the matrix elements) for the optical transitions at the k = 0 bandedge, we define a new parameter, Sopt (Eph) . Incorporating this revised element into the expression for 〈Sz 〉 , we have simulated the photon energy dependence of the OPNMR signals from bulk semi-insulating GaAs and semi-insulating InP. In earlier work, we matched calculations of electron spin polarization (alone) to features in a plot of OPNMR signal intensity versus photon energy for optical pumping (Ramaswamy et al., 2010). By incorporating an electron spin polarization which varies with pump wavelength into the penetration depth model of OPNMR signal, we are able to model features in both III-V semiconductors. The agreement between the OPNMR data and the corresponding model demonstrates that fluctuations in the OPNMR intensity have particular sensitivity to light hole-to-conduction band transitions in bulk systems. We provide detailed plots of the theoretical predictions for optical pumping transition probabilities with circularly-polarized light for both helicities of light, broken down into illustrative plots of optical magnetoabsorption and spin polarization, shown separately for heavy-hole and light-hole transitions. These plots serve as an effective roadmap of transitions, which are helpful to other researchers investigating optical pumping effects.

Modelling of OPNMR phenomena using photon energy-dependent 〈Sz〉 in GaAs and InP.

Science.gov (United States)

Wheeler, Dustin D; Willmering, Matthew M; Sesti, Erika L; Pan, Xingyuan; Saha, Dipta; Stanton, Christopher J; Hayes, Sophia E

2016-12-01

We have modified the model for optically-pumped NMR (OPNMR) to incorporate a revised expression for the expectation value of the z-projection of the electron spin, 〈S z 〉 and apply this model to both bulk GaAs and a new material, InP. This expression includes the photon energy dependence of the electron polarization when optically pumping direct-gap semiconductors in excess of the bandgap energy, E g . Rather than using a fixed value arising from coefficients (the matrix elements) for the optical transitions at the k=0 bandedge, we define a new parameter, S opt (E ph ). Incorporating this revised element into the expression for 〈S z 〉, we have simulated the photon energy dependence of the OPNMR signals from bulk semi-insulating GaAs and semi-insulating InP. In earlier work, we matched calculations of electron spin polarization (alone) to features in a plot of OPNMR signal intensity versus photon energy for optical pumping (Ramaswamy et al., 2010). By incorporating an electron spin polarization which varies with pump wavelength into the penetration depth model of OPNMR signal, we are able to model features in both III-V semiconductors. The agreement between the OPNMR data and the corresponding model demonstrates that fluctuations in the OPNMR intensity have particular sensitivity to light hole-to-conduction band transitions in bulk systems. We provide detailed plots of the theoretical predictions for optical pumping transition probabilities with circularly-polarized light for both helicities of light, broken down into illustrative plots of optical magnetoabsorption and spin polarization, shown separately for heavy-hole and light-hole transitions. These plots serve as an effective roadmap of transitions, which are helpful to other researchers investigating optical pumping effects. Copyright © 2016 Elsevier Inc. All rights reserved.

High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

International Nuclear Information System (INIS)

Dutta, P.; Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V.; Zheng, N.; Ahrenkiel, P.; Martinez, J.

2014-01-01

We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10 7  cm −2 . Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm 2 /V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Dutta, P., E-mail: pdutta2@central.uh.edu; Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V. [Department of Mechanical Engineering, University of Houston, Houston, Texas 77204 (United States); Zheng, N.; Ahrenkiel, P. [Department of Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701 (United States); Martinez, J. [Materials Evaluation Laboratory, NASA Johnson Space Center, Houston, Texas 77085 (United States)

2014-09-01

We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10{sup 7 }cm{sup −2}. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm{sup 2}/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

Quantum-size-controlled photoelectrochemical etching of semiconductor nanostructures

Science.gov (United States)

Fischer, Arthur J.; Tsao, Jeffrey Y.; Wierer, Jr., Jonathan J.; Xiao, Xiaoyin; Wang, George T.

2016-03-01

Quantum-size-controlled photoelectrochemical (QSC-PEC) etching provides a new route to the precision fabrication of epitaxial semiconductor nanostructures in the sub-10-nm size regime. For example, quantum dots (QDs) can be QSC-PEC-etched from epitaxial InGaN thin films using narrowband laser photoexcitation, and the QD sizes (and hence bandgaps and photoluminescence wavelengths) are determined by the photoexcitation wavelength.

Wavelength converter technology

DEFF Research Database (Denmark)

Kloch, Allan; Hansen, Peter Bukhave; Poulsen, Henrik Nørskov

1999-01-01

Wavelength conversion is important since it ensures full flexibility of the WDM network layer. Progress in optical wavelength converter technology is reviewed with emphasis on all-optical wavelength converter types based on semiconductor optical amplifiers.......Wavelength conversion is important since it ensures full flexibility of the WDM network layer. Progress in optical wavelength converter technology is reviewed with emphasis on all-optical wavelength converter types based on semiconductor optical amplifiers....

Meter-wavelength VLBI. III. Pulsars

International Nuclear Information System (INIS)

Vandenberg, N.R.; Clark, T.A.; Clark, W.C.; Erickson, W.C.; Resch, G.M.; Broderick, J.J.

1976-01-01

The results and analysis of observations of pulsars, especially the Crab Nebula pulsar, taken during a series of meter-wavelength very long baseline interferometry (VLBI) experiments are discussed. Based on a crude 144 MHz visibility curve which is consistent with a Gaussian brightness distribution, the measured visibilities at 196, 111, and 74 MHz were interpreted to yield apparent angular diameters (at half-power) of 0 .03 +- 0 .01, 0 .07 +- 0 .01, and 0 .18 +- 0 .01, respectively. These sizes scale approximately as wavelength-squared, and the 74 MHz size agrees with recent observations using interplanetary scintillation techniques.The VLBI-measured total flux densities lie on the extrapolation from higher frequencies of the pulsing flux densities. Variations in the total flux density up to 25 percent were observed. A lack of fine structure other than the pulsar in the nebula is indicated by our simple visibility curves. The pulse shapes observed with the interferometer are similar to single-dish measurements at 196 MHz but reveal a steady, nonpulsing component at 111 MHz. The ratio of pulsing to total power was approximately equal to one-half but varied with time. No pulsing power was detected at 74 MHz. It was found that four strong, low-dispersion pulsars were only slightly resolved

RF-MMW Dipole Antenna Arrays From Laser Illuminated GaAs

National Research Council Canada - National Science Library

Umphenour, D

1998-01-01

High resistivity photoconductive Gallium Arsenide (GaAs) can be used as elemental Hertzian dipole antenna arrays in which the time varying dipole current is produced by temporally modulating a laser (0.63um...

Manipulation of morphology and structure of the top of GaAs nanowires grown by molecular-beam epitaxy

Science.gov (United States)

Li, Lixia; Pan, Dong; Yu, Xuezhe; So, Hyok; Zhao, Jianhua

2017-10-01

Self-catalyzed GaAs nanowires (NWs) are grown on Si (111) substrates by molecular-beam epitaxy. The effect of different closing sequences of the Ga and As cell shutters on the morphology and structural phase of GaAs NWs is investigated. For the sequences of closing the Ga and As cell shutters simultaneously or closing the As cell shutter 1 min after closing the Ga cell shutter, the NWs grow vertically to the substrate surface. In contrast, when the As cell shutter is closed first, maintaining the Ga flux is found to be critical for the following growth of GaAs NWs, which can change the growth direction from [111] to . The evolution of the morphology and structural phase transition at the tips of these GaAs NWs confirm that the triple-phase-line shift mode is at work even for the growth with different cell shutter closing sequences. Our work will provide new insights for better understanding of the growth mechanism and realizing of the morphology and structure control of the GaAs NWs. Project supported partly by the MOST of China (No. 2015CB921503), the National Natural Science Foundation of China (Nos. 61504133, 61334006, 61404127), and Youth Innovation Promotion Association, CAS (No. 2017156).

Some Aspects of the RHEED Behavior of Low-Temperature GaAs Growth

International Nuclear Information System (INIS)

Nemcsics, A.

2005-01-01

The reflection high-energy electron diffraction (RHEED) behavior manifested during MBE growth on a GaAs(001) surface under low-temperature (LT) growth conditions is examined in this study. RHEED and its intensity oscillations during LT GaAs growth exhibit some particular behavior. The intensity, phase, and decay of the oscillations depend on the beam equivalent pressure (BEP) ratio and substrate temperature, etc. Here, the intensity dependence of RHEED behavior on the BEP ratio, substrate temperature, and excess of As content in the layer are examined. The change in the decay constant of the RHEED oscillations is also discussed

Density-dependent electron scattering in photoexcited GaAs

DEFF Research Database (Denmark)

Mics, Zoltán; D'’Angio, Andrea; Jensen, Søren A.

2013-01-01

—In a series of systematic optical pump - terahertz probe experiments we study the density-dependent electron scattering rate in photoexcited GaAs in a large range of carrier densities. The electron scattering time decreases by as much as a factor of 4, from 320 to 60 fs, as the electron density...

SXPS study of model GaAs(100)/electrolyte interface

Energy Technology Data Exchange (ETDEWEB)

Lebedev, Mikhail V. [A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg (Russian Federation); Mankel, Eric; Mayer, Thomas; Jaegermann, Wolfram [Institute of Material Sciences, Darmstadt University of Technology, Darmstadt (Germany)

2010-02-15

Model GaAs(100)/electrolyte interfaces are prepared in vacuum by co-adsorption of Cl{sub 2} and 2-propanol molecules at LN{sub 2} temperature. On adsorption of Cl{sub 2} molecules gallium chlorides, elemental arsenic and arsenic chlorides are formed. Co-adsorption of 2-propanol causes formation of additional GaCl{sub 3} and AsCl, as well as soluble/volatile As-based complexes, which are released from the surface depleting the sur- face by arsenic. Comparison of the As 3d and Ga 3d spectra obtained after heating the model interface to room temperature with the corresponding spectra obtained after emersion of the GaAs(100) surface from HCl/2-propanol solution allows to conclude that in HCl solution Cl{sup -} ions attack gallium sites and H{sup +} ions mostly attack arsenic sites. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Vacancies and negative ions in GaAs

International Nuclear Information System (INIS)

Corbel, C.

1991-01-01

We use positron lifetime studies performed in GaAs materials to show the defect properties which can be investigated by implanting positive positrons in semiconductors. The studies concern native and electron irradiation induced defects. These studies show that vacancy charge state and vacancy ionization levels can be determined from positron annihilation. They show also that positrons are trapped by negative ions and give information on their concentration

Investigation of the fabrication mechanism of self-assembled GaAs quantum rings grown by droplet epitaxy.

Science.gov (United States)

Tong, C Z; Yoon, S F

2008-09-10

We have directly imaged the formation of a GaAs quantum ring (QR) using droplet epitaxy followed by annealing in arsenic ambient. Based on the atomic force micrograph measurement and the analysis of surface energy, we determine that the formation of self-assembled GaAs QRs is due to the gallium atom's diffusion and crystallization driven by the gradient of surface energy. The phenomenon that GaAs is etched by the gallium droplets is reported and analyzed. It has been demonstrated that the epitaxy layers, such as AlAs and InGaP, can be used as the etching stop layer and hence can be used to control the shape and height of the QRs.

Burst annealing of high temperature GaAs solar cells

Science.gov (United States)

Brothers, P. R.; Horne, W. E.

1991-01-01

One of the major limitations of solar cells in space power systems is their vulnerability to radiation damage. One solution to this problem is to periodically heat the cells to anneal the radiation damage. Annealing was demonstrated with silicon cells. The obstacle to annealing of GaAs cells was their susceptibility to thermal damage at the temperatures required to completely anneal the radiation damage. GaAs cells with high temperature contacts and encapsulation were developed. The cells tested are designed for concentrator use at 30 suns AMO. The circular active area is 2.5 mm in diameter for an area of 0.05 sq cm. Typical one sun AMO efficiency of these cells is over 18 percent. The cells were demonstrated to be resistant to damage after thermal excursions in excess of 600 C. This high temperature tolerance should allow these cells to survive the annealing of radiation damage. A limited set of experiments were devised to investigate the feasibility of annealing these high temperature cells. The effect of repeated cycles of electron and proton irradiation was tested. The damage mechanisms were analyzed. Limitations in annealing recovery suggested improvements in cell design for more complete recovery. These preliminary experiments also indicate the need for further study to isolate damage mechanisms. The primary objective of the experiments was to demonstrate and quantify the annealing behavior of high temperature GaAs cells. Secondary objectives were to measure the radiation degradation and to determine the effect of repeated irradiation and anneal cycles.

Burst annealing of high temperature GaAs solar cells

International Nuclear Information System (INIS)

Brothers, P.R.; Horne, W.E.

1991-01-01

One of the major limitations of solar cells in space power systems is their vulnerability to radiation damage. One solution to this problem is to periodically heat the cells to anneal the radiation damage. Annealing was demonstrated with silicon cells. The obstacle to annealing of GaAs cells was their susceptibility to thermal damage at the temperatures required to completely anneal the radiation damage. GaAs cells with high temperature contacts and encapsulation were developed. The cells tested are designed for concentrator use at 30 suns AMO. The circular active area is 2.5 mm in diameter for an area of 0.05 sq cm. Typical one sun AMO efficiency of these cells is over 18 percent. The cells were demonstrated to be resistant to damage after thermal excursions in excess of 600 degree C. This high temperature tolerance should allow these cells to survive the annealing of radiation damage. A limited set of experiments were devised to investigate the feasibility of annealing these high temperature cells. The effect of repeated cycles of electron and proton irradiation was tested. The damage mechanisms were analyzed. Limitations in annealing recovery suggested improvements in cell design for more complete recovery. These preliminary experiments also indicate the need for further study to isolate damage mechanisms. The primary objective of the experiments was to demonstrate and quantify the annealing behavior of high temperature GaAs cells. Secondary objectives were to measure the radiation degradation and to determine the effect of repeated irradiation and anneal cycles

Optical properties of GaAs

International Nuclear Information System (INIS)

Akinlami, J. O.; Ashamu, A. O.

2013-01-01

We have investigated the optical properties of gallium arsenide (GaAs) in the photon energy range 0.6–6.0 eV. We obtained a refractive index which has a maximum value of 5.0 at a photon energy of 3.1 eV; an extinction coefficient which has a maximum value of 4.2 at a photon energy of 5.0 eV; the dielectric constant, the real part of the complex dielectric constant has a maximum value of 24 at a photon energy of 2.8 eV and the imaginary part of the complex dielectric constant has a maximum value of 26.0 at a photon energy of 4.8 eV; the transmittance which has a maximum value of 0.22 at a photon energy of 4.0 eV; the absorption coefficient which has a maximum value of 0.22 × 10 8 m −1 at a photon energy of 4.8 eV, the reflectance which has a maximum value of 0.68 at 5.2eV; the reflection coefficient which has a maximum value of 0.82 at a photon energy of 5.2 eV; the real part of optical conductivity has a maximum value of 14.2 × 10 15 at 4.8 eV and the imaginary part of the optical conductivity has a maximum value of 6.8 × 10 15 at 5.0 eV. The values obtained for the optical properties of GaAs are in good agreement with other results. (semiconductor physics)

Isoplanatic patch of the human eye for arbitrary wavelengths

Science.gov (United States)

Han, Guoqing; Cao, Zhaoliang; Mu, Quanquan; Wang, Yukun; Li, Dayu; Wang, Shaoxin; Xu, Zihao; Wu, Daosheng; Hu, Lifa; Xuan, Li

2018-03-01

The isoplanatic patch of the human eye is a key parameter for the adaptive optics system (AOS) designed for retinal imaging. The field of view (FOV) usually sets to the same size as the isoplanatic patch to obtain high resolution images. However, it has only been measured at a specific wavelength. Here we investigate the wavelength dependence of this important parameter. An optical setup is initially designed and established in a laboratory to measure the isoplanatic patch at various wavelengths (655 nm, 730 nm and 808 nm). We established the Navarro wide-angle eye model in Zemax software to further validate our results, which suggested high consistency between the two. The isoplanatic patch as a function of wavelength was obtained within the range of visible to near-infrared, which can be expressed as: θ=0.0028 λ - 0 . 74. This work is beneficial for the AOS design for retinal imaging.

Femtosecond coherent emission from GaAs bulk microcavities

Science.gov (United States)

Gurioli, Massimo; Bogani, Franco; Ceccherini, Simone; Colocci, Marcello; Beltram, Fabio; Sorba, Lucia

1999-02-01

The emission from a λ/2 GaAs bulk microcavity resonantly excited by femtosecond pulses has been characterized by using an interferometric correlation technique. It is found that the emission is dominated by the coherent signal due to light elastically scattered by disorder, and that scattering is predominantly originated from the lower polariton branch.

Tunneling effect on double potential barriers GaAs and PbS

Science.gov (United States)

Prastowo, S. H. B.; Supriadi, B.; Ridlo, Z. R.; Prihandono, T.

2018-04-01

A simple model of transport phenomenon tunnelling effect through double barrier structure was developed. In this research we concentrate on the variation of electron energy which entering double potential barriers to transmission coefficient. The barriers using semiconductor materials GaAs (Galium Arsenide) with band-gap energy 1.424 eV, distance of lattice 0.565 nm, and PbS (Lead Sulphide) with band gap energy 0.41 eV distance of lattice is 18 nm. The Analysisof tunnelling effect on double potentials GaAs and PbS using Schrodinger’s equation, continuity, and matrix propagation to get transmission coefficient. The maximum energy of electron that we use is 1.0 eV, and observable from 0.0025 eV- 1.0 eV. The shows the highest transmission coefficient is0.9982 from electron energy 0.5123eV means electron can pass the barriers with probability 99.82%. Semiconductor from materials GaAs and PbS is one of selected material to design semiconductor device because of transmission coefficient directly proportional to bias the voltage of semiconductor device. Application of the theoretical analysis of resonant tunnelling effect on double barriers was used to design and develop new structure and combination of materials for semiconductor device (diode, transistor, and integrated circuit).

Subnanosecond, high voltage photoconductive switching in GaAs

Energy Technology Data Exchange (ETDEWEB)

Druce, R.L.; Pocha, M.D.; Griffin, K.L. (Lawrence Livermore National Lab., CA (USA)); O' Bannon, B.J. (Rockwell International Corp., Anaheim, CA (USA))

1990-01-01

We are conducting research on the switching properties of photoconductive materials to explore their potential for generating high-power microwaves (HPM) and for high rep-rate switching. We have investigated the performance of Gallium Arsenide (GaAs) in linear mode (the conductivity of the device follows the optical pulse) as well as an avalanche-like mode (the optical pulse only controls switch closing). Operating in the linear mode, we have observed switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps at several kV/cm fields using neutron irradiated GaAs. In avalanche and lock-on modes, high fields are switched with lower laser pulse energies, resulting in higher efficiencies; but with measurable switching delay and jitter. We are currently investigating both large area (1 cm{sup 2}) and small area (<1 mm{sup 2}) switches illuminated by AlGaAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 {mu}m.

X-ray imaging bilinear staggered GaAs detectors

Energy Technology Data Exchange (ETDEWEB)

Achmadullin, R.A.; Dvoryankin, V.F. E-mail: vfd217@ire216.msk.su; Dvoryankina, G.G.; Dikaev, Y.M.Yu.M.; Krikunov, A.I.; Kudryashov, A.A.; Panova, T.M.; Petrov, A.G.; Telegin, A.A

2004-09-21

The multichannel bilinear X-ray detector based on epitaxial GaAs structures is developed to obtain a digital X-ray image. Each detector operates in photovoltaic mode without reverse bias that enables almost complete elimination of detector noise arising due to leakage currents. The sensitivity range of the epitaxial GaAs photovoltaic X-ray detector covers the effective energies from 8 to 120 keV. A maximum response of the detector operating in the short-circuit mode was observed at an energy of 35 keV and amounted to 30 {mu}A min/(Gy cm{sup 2}). The multichannel detector was made of 1024 pixels with pitch of 0.8 mm. The spatial resolution of double staggered sensor row is twice as high as the resolution of that of single sensor row with the same pitch. Measured spatial resolution is 1.2 line-pairs/mm, contrast sensitivity not worse 1% and dynamic range defined as the ratio of maximum detectable X-ray signal to electronic noise level more than 2000 are received.

X-ray imaging bilinear staggered GaAs detectors

International Nuclear Information System (INIS)

Achmadullin, R.A.; Dvoryankin, V.F.; Dvoryankina, G.G.; Dikaev, Y.M.Yu.M.; Krikunov, A.I.; Kudryashov, A.A.; Panova, T.M.; Petrov, A.G.; Telegin, A.A.

2004-01-01

The multichannel bilinear X-ray detector based on epitaxial GaAs structures is developed to obtain a digital X-ray image. Each detector operates in photovoltaic mode without reverse bias that enables almost complete elimination of detector noise arising due to leakage currents. The sensitivity range of the epitaxial GaAs photovoltaic X-ray detector covers the effective energies from 8 to 120 keV. A maximum response of the detector operating in the short-circuit mode was observed at an energy of 35 keV and amounted to 30 μA min/(Gy cm 2 ). The multichannel detector was made of 1024 pixels with pitch of 0.8 mm. The spatial resolution of double staggered sensor row is twice as high as the resolution of that of single sensor row with the same pitch. Measured spatial resolution is 1.2 line-pairs/mm, contrast sensitivity not worse 1% and dynamic range defined as the ratio of maximum detectable X-ray signal to electronic noise level more than 2000 are received

Disruption of Higher Order DNA Structures in Friedreich's Ataxia (GAA)(n) Repeats by PNA or LNA Targeting

DEFF Research Database (Denmark)

Bergquist, Helen; Rocha, Cristina S. J.; Alvarez-Asencio, Ruben

2016-01-01

Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigen...

Origin of the suppression in low frequency terahertz conductivity in dilute GaAs nitride and bismide alloys

DEFF Research Database (Denmark)

Cocker, Tylor; Lu, Xianfeng; Cooke, David

We have performed time-resolved terahertz spectroscopy on GaAs1-xBix (x=7%) and observed a low-frequency suppression of the real conductivity previously seen only in dilute GaAs nitrides. We have developed a modified Drude model with a frequency-dependent scattering time that provides excellent...

Influence of substrate orientation on the structural properties of GaAs nanowires in MOCVD

Energy Technology Data Exchange (ETDEWEB)

Muhammad, R., E-mail: rosnita@utm.my; Othaman, Z., E-mail: zulothaman@gmail.com; Ibrahim, Z., E-mail: zuhairi@utm.my; Sakrani, S., E-mail: samsudi3@yahoo.com [Faculty of Science, UniversitiTeknologi Malaysia, 81310 UTM, Johor (Malaysia); Wahab, Y., E-mail: wyussof@gmail.com [Razak School, UniversitiTeknologi Malaysia, 54100 Kuala Lumpur (Malaysia)

2016-04-19

In this study, the effect of substrate orientation on the structural properties of GaAs nanowires grown by a metal organic chemical vapor deposition has been investigated. Gold colloids were used as catalyst to initiate the growth of nanowiresby the vapour-liquid-solid (VLS) mechanism. From the field-emission scanning electron microscopy (FE-SEM), the growth of the nanowires were at an elevation angle of 90°, 60°, 65° and 35° with respect to the GaAs substrate for (111)B, (311)B, (110) and (100) orientations respectively. The preferential NW growth direction is always <111>B. High-resolution transmission electron microscope (HRTEM) micrograph showed the NWs that grew on the GaAs(111)B has more structural defects when compared to others. Energy dispersive X-ray analysis (EDX) indicated the presence of Au, Ga and As. The bigger diameter NWs dominates the (111)B substrate surface.

GaAs detectors with an ultra-thin Schottky contact for spectrometry of charged particles

Energy Technology Data Exchange (ETDEWEB)

Chernykh, S.V., E-mail: chsv_84@mail.ru [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Chernykh, A.V. [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Didenko, S.I.; Baryshnikov, F.M. [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Burtebayev, N. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Institute of Nuclear Physics, Almaty (Kazakhstan); Britvich, G.I. [Institute of High Energy Physics, Protvino, Moscow region (Russian Federation); Chubenko, A.P. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow (Russian Federation); Guly, V.G.; Glybin, Yu.N. [LLC “SNIIP Plus”, Moscow (Russian Federation); Zholdybayev, T.K.; Burtebayeva, J.T.; Nassurlla, M. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Institute of Nuclear Physics, Almaty (Kazakhstan)

2017-02-11

For the first time, samples of particle detectors based on high-purity GaAs epilayers with an active area of 25 and 80 mm{sup 2} and an ultra-thin Pt Schottky barrier were fabricated for use in the spectrometry of charged particles and their operating characteristics were studied. The obtained FWHM of 14.2 (for 25 mm{sup 2} detector) and 15.5 keV (for 80 mm{sup 2} detector) on the 5.499 MeV line of {sup 238}Pu is at the level of silicon spectrometric detectors. It was found that the main component that determines the energy resolution of the detector is a fluctuation in the number of collected electron–hole pairs. This allows us to state that the obtained energy resolution is close to the limit for VPE GaAs. - Highlights: • VPE GaAs particle detectors with an active area of 25 and 80 mm{sup 2} were fabricated. • 120 Å ultra-thin Pt Schottky barrier was used as a rectifying contact. • The obtained FWHM of 14.2 keV ({sup 238}Pu) is at the level of Si spectrometric detectors. • Various components of the total energy resolution were analyzed. • It was shown that obtained energy resolution is close to its limit for VPE GaAs.

Photoacoustic study of the effect of doping concentration on the transport properties of GaAs epitaxial layers

NARCIS (Netherlands)

George, S.D.; Dilna, S.; Prasanth, R.; Radhakrishnan, P.; Vallabhan, C.P.G.; Nampoori, V.P.N.

2003-01-01

We report a photoacoustic (PA) study of the thermal and transport properties of a GaAs epitaxial layer doped with Si at varying doping concentration, grown on GaAs substrate by molecular beam epitaxy. The data are analyzed on the basis of Rosencwaig and Gersho's theory of the PA effect. The

Do shorter wavelengths improve contrast in optical mammography?

International Nuclear Information System (INIS)

Taroni, P; Pifferi, A; Torricelli, A; Spinelli, L; Danesini, G M; Cubeddu, R

2004-01-01

The detection of tumours with time-resolved transmittance imaging relies essentially on blood absorption. Previous theoretical and phantom studies have shown that both contrast and spatial resolution of optical images are affected by the optical properties of the background medium, and high absorption and scattering are generally beneficial. Based on these observations, wavelengths shorter than presently used (680-780 nm) could be profitable for optical mammography. A study was thus performed analysing time-resolved transmittance images at 637, 656, 683 and 785 nm obtained from 26 patients bearing 16 tumours and 15 cysts. The optical contrast proved to increase upon decreasing wavelengths for the detection of cancers in late-gated intensity images, with higher gain in contrast for lesions of smaller size (<1.5 cm diameter). For cysts either a progressive increase or decrease in contrast with wavelength was observed in scattering images

Influence of implantation conditions of He+ ions on the structure of a damaged layer in GaAs(001)

International Nuclear Information System (INIS)

Shcherbachev, Kirill; Bailey, Melanie J.

2011-01-01

An investigation into the influence of implantation conditions (dose, energy, and target temperature) of He + ions on the damage structure of GaAs (100) substrates was performed by HRXRD, scanning electron microscopy, and Nomarski microscopy. Blistering is shown to become apparent as characteristic features of isolines in RSMs. We propose that the formation of the defects yielding a characteristic XRDS is defined by the behavior of implanted atoms in the GaAs matrix, depending on two competing processes: (1) formation of the gas-filled bubbles; (2) diffusion of the He atoms from the bubbles toward the surface and deep into the GaAs substrate. We conclude that the gas-filled bubbles change the structure of the irradiated layer, resulting in the formation of strained crystalline areas of the GaAs matrix. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Controlling the opto-mechanics of a cantilever in an interferometer via cavity loss

Energy Technology Data Exchange (ETDEWEB)

Schmidsfeld, A. von, E-mail: avonschm@uos.de; Reichling, M., E-mail: reichling@uos.de [Fachbereich Physik, Universität Osnabrück, Barbarastraße 7, 49076 Osnabrück (Germany)

2015-09-21

In a non-contact atomic force microscope, based on interferometric cantilever displacement detection, the optical return loss of the system is tunable via the distance between the fiber end and the cantilever. We utilize this for tuning the interferometer from a predominant Michelson to a predominant Fabry-Pérot characteristics and introduce the Fabry-Pérot enhancement factor as a quantitative measure for multibeam interference in the cavity. This experimentally easily accessible and adjustable parameter provides a control of the opto-mechanical interaction between the cavity light field and the cantilever. The quantitative assessment of the light pressure acting on the cantilever oscillating in the cavity via the frequency shift allows an in-situ measurement of the cantilever stiffness with remarkable precision.

GaAs low-energy X-ray radioluminescence nuclear battery

Science.gov (United States)

Zhang, Zheng-Rong; Liu, Yun-Peng; Tang, Xiao-Bin; Xu, Zhi-Heng; Yuan, Zi-Cheng; Liu, Kai; Chen, Wang

2018-01-01

The output properties of X-ray radioluminescence (RL) nuclear batteries with different phosphor layers were investigated by using low-energy X-ray. Results indicated that the values of electrical parameters increased as the X-ray energy increased, and the output power of nuclear battery with ZnS:Cu phosphor layer was greater than those of batteries with ZnS:Ag, (Zn,Cd)S:Cu or Y2O3:Eu phosphor layers under the same excitation conditions. To analyze the RL effects of the phosphor layers under X-ray excitation, we measured the RL spectra of the different phosphor layers. Their fluorescence emissions were absorbed by the GaAs device. In addition, considering luminescence utilization in batteries, we introduced an aluminum (Al) film between the X-ray emitter and phosphor layer. Al film is a high performance reflective material and can increase the fluorescence reaching the GaAs photovoltaic device. This approach significantly improved the output power of the battery.

2.5 Gb/s laser-driver GaAS IC

DEFF Research Database (Denmark)

Riishøj, Jesper

1993-01-01

A laser-diode driver GaAs IC incorporating an optional NRZ/RZ (non-return-to-zero/return-to-zero) conversion facility, having ECL (emitter-coupled logic) and SCFL (source-coupled FET logic)-compatible inputs and providing a 0-60-mA adjustable output current into a 50-Ω/5-V termination at bit rates...... obtained. To verify laser driving performance a back-to-back optical-fiber transmission experiment was performed, giving good optical eye diagrams at 2.5 Gb/s. The electrooptical interplay between laser-diode driver and laser-diode has been demonstrated using SPICE simulations...... up to 2 Gb/s NRZ and maintaining a clear eye opening of 50 mA at 2.5 Gb/s NRZ bit rate has been designed, using a commercial 1-μm gate-length (Fτ=12 GHz) GaAs MESFET foundry service. The high maximum output current is obtained by implementing the output driver as a cascode differential amplifier...

Pseudo-Rhombus-Shaped Subwavelength Crossed Gratings of GaAs for Broadband Antireflection

International Nuclear Information System (INIS)

Chen Xi; Zhang Jing; Song Guo-Feng; Chen Liang-Hui; Fan Zhong-Chao

2010-01-01

Holographic lithography coupled with the nonlinear response of photoresist to the exposure is adopted to fabricate porous photoresist (PR) mask. Conventional dot PR mask is also generated, and both patterns are transferred into a underlying GaAs substrate by the optimal dry etching process to obtain tapered subwavelength crossed gratings (SWCGs) to mimic the moth-eye structure. In comparison of the experiment and simulation, the closely-packed pseudo-rhombus-shaped GaAs SWCGs resulting from the porous mask outperforms the conical counterpart which comes from the dot mask, and achieves a reported lowest mean spectral reflectance of 1.1%. (fundamental areas of phenomenology(including applications))

Magnetic Properties of Fe(001) Thin Films on GaAs(001) Deposited by RF Magnetron Sputtering

International Nuclear Information System (INIS)

Ikeya, Hirokazu; Takahashi, Yutaka; Inaba, Nobuyuki; Kirino, Fumiyoshi; Ohtake, Mitsuru; Futamoto, Masaaki

2011-01-01

Fe thin films, down to 6 nm thick, were prepared on GaAs(001) substrates by RF magnetron sputtering. The x-ray diffraction (XRD) analyses show that the epitaxial thin films of Fe(001) were grown with cube-on-cube orientation on GaAs(001). Magnetic properties were investigated by vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) spectroscopy. The magnetization curves obtained by applying in-plane magnetic fields indicate that easy (hard) direction is along [100] ([110]) and the saturation magnetization is close to the bulk values. The in-plane magnetic anisotropy measured by FMR shows four-fold symmetry, as expected for bcc Fe. We did not observe the in-plane uniaxial magnetic anisotropy reported on the MBE-grown Fe films on GaAs substrates.

Interface magnetism of iron grown on sulfur and hydrogen passivated GaAs(001)

International Nuclear Information System (INIS)

Kardasz, B.; Watkins, S. P.; Montoya, E. A.; Burrowes, C.; Girt, E.; Heinrich, B.

2012-01-01

Sulfur (S) and hydrogen (H) atom passivated GaAs(001) templates were used for deposition of ultrathin crystalline Fe films using molecular beam epitaxy, where the Fe thickness ranged from 10 to 45 atomic layers. Reflection high-energy electron diffraction patterns showed that the S- and H-passivated surfaces had no and very weak (1 x 2) superlattice reconstructions, respectively. This indicates that these GaAs(001) templates have a square-like symmetry. Magnetic anisotropies were investigated using the in-plane angular dependence of ferromagnetic resonance at 36 GHz. The in-plane cubic and uniaxial anisotropies and perpendicular uniaxial field were described by bulk and interface contributions, indicating that the Fe films have a high lattice coherence. The magnetic properties of the Fe films were compared to those grown on more commonly used GaAs(001) templates having a (4 x 6) reconstruction with an As-rich in-plane uniaxial symmetry. The Fe films grown on S-passivated templates exhibited unique magnetic properties caused by a decreased lattice spacing compared to the bulk Fe.

Interface magnetism of iron grown on sulfur and hydrogen passivated GaAs(001)

Energy Technology Data Exchange (ETDEWEB)

Kardasz, B.; Watkins, S. P.; Montoya, E. A.; Burrowes, C.; Girt, E.; Heinrich, B.

2012-04-01

Sulfur (S) and hydrogen (H) atom passivated GaAs(001) templates were used for deposition of ultrathin crystalline Fe films using molecular beam epitaxy, where the Fe thickness ranged from 10 to 45 atomic layers. Reflection high-energy electron diffraction patterns showed that the S- and H-passivated surfaces had no and very weak (1 x 2) superlattice reconstructions, respectively. This indicates that these GaAs(001) templates have a square-like symmetry. Magnetic anisotropies were investigated using the in-plane angular dependence of ferromagnetic resonance at 36 GHz. The in-plane cubic and uniaxial anisotropies and perpendicular uniaxial field were described by bulk and interface contributions, indicating that the Fe films have a high lattice coherence. The magnetic properties of the Fe films were compared to those grown on more commonly used GaAs(001) templates having a (4 x 6) reconstruction with an As-rich in-plane uniaxial symmetry. The Fe films grown on S-passivated templates exhibited unique magnetic properties caused by a decreased lattice spacing compared to the bulk Fe.

Promotion effect of monovalent metals (K and Cs) on the GaAs (110) surface oxidation

International Nuclear Information System (INIS)

Valeri, S.; Sberveglieri, P.; Angeli, E.

1987-01-01

The effect of thin (∼ 1 monolayer) overlayers of low electronegativity metals (Cs and K) on the RT oxidation behaviour of GaAs(110) cleavage surface is studied. This study was with Auger and Photoemission spectroscopies. Attention has been focused on the core-valence-valence and Auger lineshapes on the Ga and As 3d peaks. Presence of the alkali metal enhances the GaAs (110) oxidation rate several orders of magnitude above the clean surface value has been found. The range 0-100 Langmuir is investigated in detail. The oxidation process of the GaAs(110) surface in the presence of both K and Cs overlayer follows a multi-step kinetic and reaches a saturation at exposure lower than 100 Langmuir. Both Ga and As atoms are involved in the oxygen bonding. The metal enhanced semiconductor oxidation is generally reported to be a process involving predominantly the semiconductor surface atoms. However in the Cs - and K - GaAs case, an involvement of the alkali metal atoms too, reflected in the shape modification of their Auger line has been found. The promotion effect of K and Cs is discussed in terms of their low electronegativity and in comparison with the results recently reported in the literature for the other low electronegativity metals

Sulfur passivation and contact methods for GaAs nanowire solar cells

International Nuclear Information System (INIS)

Tajik, N; Peng, Z; Kuyanov, P; LaPierre, R R

2011-01-01

The effect of sulfur passivation on core-shell p-n junction GaAs nanowire (NW) solar cells has been investigated. Devices of two types were investigated, consisting of indium tin oxide contact dots or opaque Au finger electrodes. Lateral carrier transport from the NWs to the contact fingers was achieved via a p-doped GaAs surface conduction layer. NWs between the opaque contact fingers had sidewall surfaces exposed for passivation by sulfur. The relative cell efficiency increased by 19% upon passivation. The contribution of the thin film grown between the NWs to the total cell efficiency was estimated by removing the NWs using a sonication procedure. Mechanisms of carrier transport and photovoltaic effects are discussed on the basis of spatially resolved laser scanning measurements.

Diffusion of $^{56}$Co in GaAs and SiGe alloys

CERN Multimedia

Koskelo, O K

2007-01-01

Following our previous diffusion studies performed with the modified radiotracer technique, we propose to determine the diffusion of cobalt in GaAs and SiGe alloys under intrinsic conditions. In the literature only three previous studies for Co diffusion in GaAs may be found and the results differ by over four orders of magnitude from each other. For Co diffusion in SiGe alloys no previous data is available in the literature. For Co diffusion in Ge one study may be found but the results have been obtained with material having increased dislocation density. For dislocation-free material no previous measurements are available. For such experiments we ask for two runs of 3 shifts (total of 6 shifts) with $^{56}$Co$^{+}$ ion beam.

Bismuth alloying properties in GaAs nanowires

Energy Technology Data Exchange (ETDEWEB)

Ding, Lu [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, PO Box 72, Beijing 100876 (China); Lu, Pengfei, E-mail: photon.bupt@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, PO Box 72, Beijing 100876 (China); Cao, Huawei; Cai, Ningning; Yu, Zhongyuan [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, PO Box 72, Beijing 100876 (China); Gao, Tao [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Wang, Shumin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg (Sweden)

2013-09-15

First-principles calculations have been performed to investigate the structural, electronic and optical properties of bismuth alloying in GaAs nanowires. A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration and the band edge shifts when spin–orbit coupling (SOC) is considered. The insertion of Bi atom leads to hybridization of Ga/As/Bi p states which contributes a lot around Fermi level. Scissor effect is involved. The optical properties are presented, including dielectric function, optical absorption spectra and reflectivity, which are also varied with the increasing of Bi concentrations. - Graphical abstract: Top view of Bi-doped GaAs nanowires. Ga, As, and Bi atoms are denoted with grey, purple and red balls, respectively. Display Omitted - Highlights: • A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. • The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration. • The band edge shifts when spin–orbit coupling (SOC) is considered. • The insertion of Bi atom leads to hybridization of Ga/As/Bi p states.

High Quality GaAs Epilayers Grown on Si Substrate Using 100 nm Ge Buffer Layer

Directory of Open Access Journals (Sweden)

Wei-Cheng Kuo

2016-01-01

Full Text Available We present high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers. The thin Ge buffer layers were modulated by hydrogen flow rate from 60 to 90 sccm to improve crystal quality by electron cyclotron resonance chemical vapor deposition (ECR-CVD at low growth temperature (180°C. The GaAs and Ge epilayers quality was verified by X-ray diffraction (XRD and spectroscopy ellipsometry (SE. The full width at half maximum (FWHM of the Ge and GaAs epilayers in XRD is 406 arcsec and 220 arcsec, respectively. In addition, the GaAs/Ge/Si interface is observed by transmission electron microscopy (TEM to demonstrate the epitaxial growth. The defects at GaAs/Ge interface are localized within a few nanometers. It is clearly showed that the dislocation is well suppressed. The quality of the Ge buffer layer is the key of III–V/Si tandem cell. Therefore, the high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers is suitable to develop the low cost and high efficiency III–V/Si tandem solar cells.

In-plane wavelength division de-multiplexing using photonic crystals

DEFF Research Database (Denmark)

Frandsen, Lars Hagedorn; Harpøth, Anders; Hede, K. K.

We demonstrate a novel concept for in-plane coarse wavelength division de-multiplexing in integrated photonic circuits utilizing planar photonic crystal waveguides (PhCWs) fabricated in a silicon-on-insulator material. The filtering of wavelength channels is realized by shifting the cut......-off frequency of the fundamental photonic bandgap mode. The shift is obtained by modifying the size of the border holes in consecutive sections of the PhCW1. Simulations and experimental proof-of-principle of the four-channel de-multiplexer will be presented. 1A. Adibi et al., Electron. Lett. 36, 1376...

Strong coupling between bi-dimensional electron gas and nitrogen localized states in heavily doped GaAs1-xN x structures

International Nuclear Information System (INIS)

Hamdouni, A.; Bousbih, F.; Ben Bouzid, S.; Oueslati, M.; Chtourou, R.; Harmand, J.C.

2005-01-01

We report a low-temperature photoluminescence spectra (LTPL) of GaAs 1-x N x layers and two-dimension electron gas (2DEG) GaAs 1-x N x /AlGaAs modulation doped heterostructure grown on GaAs substrates by molecular beam epitaxy (MBE) with low nitrogen content [N] = 2 x 10 18 cm -3 . At low temperature, PL spectra of GaAs 1-x N x layers are governed by several features associate to the excitons bound to nitrogen complexes, these features disappear in (2DEG) GaAs 1-x N x /AlGaAs modulation doped heterostructure and the PL peak energy decrease with the laser power excitation. This effect is explained by the strongly coupling of the (2DEG) fundamental state with the nitrogen localized states. An activated energy of about 55 meV is deduced by photoluminescence measurements in the 10-300 K range for a laser power excitation P = 6 W/cm 2

Homozygotic intronic GAA mutation in three siblings with late-onset Pompe's disease Mutação homozigótica intrônica no gene GAA em três irmãos com doença de Pompe de início tardio

Directory of Open Access Journals (Sweden)

Anderson Kuntz Grzesiuk

2010-04-01

Full Text Available Pompe's disease (PD is a metabolic myopathy caused by the accumulation of lysosomal glycogen, secondary to acid α-glucosidase (GAA enzyme deficiency. Childhood and late-onset forms are described, differing by the age of onset and symptoms. In this study were analyzed affected siblings with Pompe's disease (PD and their distinct clinical and pathological presentations. METHOD: Diagnosis was performed by the clinical presentation of limb-girdle dystrophies and respiratory compromise. Confirmatory diagnoses were conducted by muscle biopsy, GAA activity measurement and by GAA gene genotyping. RESULTS: The findings suggested muscular involvement due to GAA deficiency. GAA genotyping showed they are homozygous for the c.-32-3C>A mutation. CONCLUSION: Herein we reported a family where three out of five siblings were diagnosed with late-onset PD, although it is a rare metabolic disease inherited in an autossomal recessive manner. We emphasize the importance of including this presentation within the differential diagnoses of the limb-girdle dystrophies once enzyme replacement therapy is available.A doença de Pompe (DP é uma miopatia originada do acúmulo lisossomal de glicogênio, devido à deficiência da enzima α-glicosidase ácida (GAA, sendo descritas formas de inicio precoce e tardio. Neste estudo analisamos retrospectivamente o perfil clinico e patológico de 3 irmãos portadores de doença de Pompe de inicio tardio. MÉTODO: O diagnóstico foi realizado mediante apresentação clinica de distrofia de cinturas associado a comprometimento respiratório, sendo confirmado por biópsia muscular e análise da atividade e genotipagem da GAA. RESULTADOS: Os exames clínicos e laboratoriais demonstram envolvimento muscular devido à deficiência da GAA, com uma mutação c.-32-3C>A em homozigose. CONCLUSÃO: Relatamos os aspectos clínicos e laboratoriais de 3 irmãos afetados por doença de Pompe de início tardio. Enfatizamos a importância de

Isolating GaSb Membranes Grown Metamorphically on GaAs Substrates Using Highly Selective Substrate Removal Etch Processes

Science.gov (United States)

Renteria, E. J.; Muniz, A. J.; Addamane, S. J.; Shima, D. M.; Hains, C. P.; Balakrishnan, G.

2015-05-01

The etch rates of NH4OH:H2O2 and C6H8O7:H2O2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH4OH:H2O2 solution has a greater etch rate differential for the GaSb/GaAs material system than C6H8O7:H2O2 solution. The selectivity of NH4OH:H2O2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11,000 ± 2000, whereas that of C6H8O7:H2O2 has been measured up to 143 ± 2. The etch contrast has been verified by isolating 2- μm-thick GaSb epilayers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high- resolution x-ray diffraction and atomic force microscopy.

Antisites and anisotropic diffusion in GaAs and GaSb

KAUST Repository

Tahini, H. A.; Bracht, H.; Chroneos, Alexander; Grimes, R. W.; Murphy, S. T.; Schwingenschlö gl, Udo

2013-01-01

The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport

Optical Properties of InGaAs/ GaAs Multi Quantum Wells Structure Grown By Molecular Beam Epitaxy

International Nuclear Information System (INIS)

Mohd Sharizal Alias; Mohd Fauzi Maulud; Mohd Razman Yahya; Abdul Fatah Awang Mat; Suomalainen, Soile

2008-01-01

Inclusive analysis on the optical characteristics of InGaAs/ GaAs QW structure for 980 nm semiconductor laser operation is presented from experimental and theoretical point of view. The InGaAs/ GaAs quantum well structure is grown by molecular beam epitaxy at different indium composition and quantum well thickness for optical characteristic comparison. Photoluminescence spectra from the measurement show that the spectrum is in good agreement with the simulation results. Detail simulation on the material gain for the InGaAs/ GaAs quantum well as a function of carrier densities and operating temperature is also performed in order to optimize the semiconductor laser design for device fabrication. (author)

X-ray diffraction study on pressure-induced phase transformation in nanocrystalline GaAs

DEFF Research Database (Denmark)

Jiang, Jianzhong; Olsen, J. S.; Gerward, Leif

2002-01-01

We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two-component ......We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two...

Stable Amplification and High Current Drop Bistable Switching in Supercritical GaAs Tills

DEFF Research Database (Denmark)

Izadpanah, S.H; Jeppsson, B; Jeppesen, Palle

1974-01-01

Bistable switching with current drops of 40% and switching times of 100 ps are obtained in pulsed operation of 10¿m supercritically doped n+ nn+ GaAs Transferred Electron Devices (TEDs). When CW-operated the same devices exhibit a 5-17 GHz bandwidth for the stable negative resistance.......Bistable switching with current drops of 40% and switching times of 100 ps are obtained in pulsed operation of 10¿m supercritically doped n+ nn+ GaAs Transferred Electron Devices (TEDs). When CW-operated the same devices exhibit a 5-17 GHz bandwidth for the stable negative resistance....