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We report experimental evidence that an ErAs quantum-dot array in a GaAs matrix under 1550 nm pulsed excitation produces cooperative spontaneous emission-Dicke superradiance-in the terahertz frequency region at room temperature., Comment: 8 pages, 4 figures

Here we present an original study of the effect of hydration on Terahertz absorption signatures in biomolecular (lactose monohydrate and biotin) and bioparticles( Bacillus thuringiensis and Bacillus cereus spores). We observe "read-shift" in center frequency with increasing hydration in all samples, consistent with Lorentzian-oscillator behavior. But the effect of hydration on linewidth is ambiguous, sometimes increasing the linewdith (consistent with Lorentzian behaviour) and sometimes decreasing the linewidth.

We report here the first RF noise measurements on two designs of n-doped GaN/AlN double-barrier resonant tunneling diodes (RTDs), each having a room-temperature negative differential resistance (NDR) and also strong near-UV light emission. The measurements are made with a standard, un-isolated RF receiver and calibration is made using a substitution-resistor/hot-cold radiometric technique which works in the positive differential resistance (PDR) region but not the NDR region. A high-quality InGaAs/AlAs double-barrier RTD is used as a control sample and displays shot noise suppression down to $\Gamma\approx$0.5 in the PDR region, as expected. The GaN/AlN RTDs display both shot-noise enhancement and suppression in the PDR regions, but no obvious sign of sudden shot-noise enhancement in the threshold bias region of light emission. This supports the hypothesis that the holes required for light emission are created by electronic (Zener) interband tunneling, not impact ionization. Further the minimum shot-noise factor of $\Gamma\sim$ 0.34 suggests that the GaN/AlN RTDs are acting like triple-barrier devices., Comment: 10 pages, 5 figures

We report strong light emission from a room-temperature n-type unipolar-doped In0.53Ga0.47As/AlAs double-barrier resonant-tunneling diode (DBRTD) precisely at the In0.53Ga0.47As band-edge near 1650 nm. The emission characteristics are very similar to what was observed recently in GaN/AlN DBRTDs, both of which suggest that the mechanism for emission is cross-gap electron-hole recombination via resonant- and Zener co-tunneling of electrons, the latter mechanism generating the required holes. Analysis shows that because of the relatively small bandgap, the Zener tunneling probability can be large in this In0.53Ga0.47As/AlAs DBRTD, and is a mechanism that may have been overlooked in the longstanding literature. The universal nature of the co-tunneling is best supported by the factor (EG)2/F in the Kane tunneling probability, which is nearly the same at the peak voltage of the In0.53Ga0.47As and GaN DBRTDs.

We report anomalous critical transport behavior in a GaAs structure containing a dense array of ErAs quantum dots. The structure displays a voltage (electric field)-controlled insulator-to-metal transition and strong hysteresis in the Kondo-like current-vs-temperature characteristic, with critical temperatures as high as 50 K. We attribute this behavior to a strong distributed Kondo resonance between the quantum dots after the Coulomb blockade of the array is lifted. This is consistent with a high sensitivity of the phase transition to a small external magnetic field that we have observed in the Voigt configuration, and a phenomenological model based on the RKKY interaction within a quantum dot and the cooperative Kondo-resonance amongst quantum dots., 15 pages, 6 figures

In several species of invertebrates there is good evidence for the presence of L-glutamate in the central and peripheral nervous system and evidence for both classes of ionotropic receptor

The photoconductions of ultrafast InGaAs:ErAs nanocomposites at low temperatures were investigated. The parabolic Tauc edge as well as the exponential Urbach tail are identified in the absorption spectrum. The Tauc edge supports that the density of states at the bottom of conduction band is proportional to the square root of energy. The Urbach edge is attributed to interband transition caused by smooth microscopic internal fields. The square root of mean-squared internal fields, whose distribution is Gaussian, is found in the order of $10^{5}$V/cm, agreeing very well with the theoretical predictions by Esser (B. ~ Esser, Phys. stat. sol. (b), vol. 51, 735 (1972)).

This article presents studies on low-field electrical conduction in the range 4-to-300 K for a ultrafast material: InGaAs:ErAs grown by molecular beam epitaxy. The unique properties include nano-scale ErAs crystallines in host semiconductor, a deep Fermi level, and picosecond ultrafast photocarrier recombination. As the temperature drops, the conduction mechanisms are in the sequence of thermal activation, nearest-neighbor hopping, variable-range hopping, and Anderson localization. In the low-temperature limit, finite-conductivity metallic behavior, not insulating, was observed. This unusual conduction behavior is explained with the Abrahams scaling theory.

The low-frequency power spectrum has been measured for ErAs:InAlGaAs diodes and shows at least a ten-times reduction of 1/f noise compared to traditional Al Schottky diodes on the same semiconductor material. These junctions are grown by molecular beam epitaxy, preventing oxidation and other contamination at the junction. The major noise source for these devices is attributed to the sidewalls and not the junction itself. Low-frequency oscillations have also been observed and associated with a deep trap level estimated to be similar to 200 meV below the conduction band edge by the comparison of diodes with different InAlGaAs compositions and confirmed by deep level transient spectroscopy. This deep level could be associated to erbium incorporation in the depletion region.

An investigation of the optical transmission properties of semimetallic ErAs films grown by molecular beam epitaxy reveals a maximum in transmission around 1.55 mu m. The semitransparent window extends from similar to 1.5 to 2.3 mu m. These films were found to have resistivities less than 7x10(-5) Omega cm and permit similar to 85% transmission for a 150 nm film and similar to 97% transmission for a 15 nm film with respect to a GaAs substrate at 1.55 mu m. These results suggest that ErAs may be a useful material for applications requiring transparent contacts from 1.5 to 2.3 mu m. Polycrystalline films of ErAs were grown on sapphire substrates to investigate optical properties of ErAs in the visible region. (c) 2006 American Institute of Physics.

We demonstrate a molecular beam epitaxy growth technique to create intentionally textured interfaces between semimetallic ErAs and GaAs that result in interface orientations that are different from the substrate. To grow the textured interfaces, ErAs is deposited on (100) GaAs and islands form in an island growth mode. Enough GaAs is then deposited to fill the space between islands with semiconductor. More ErAs is deposited on the ErAs/GaAs surface and the new ErAs islands are thought to nucleate on the exposed top surface of the partially covered islands. The process is repeated to "stack" the islands. By quadratically increasing the amount of ErAs deposited in each repetition, the islands form into cones/pyramids that coalesce into a complete film with an intentionally roughened interface. Compared to a smooth interface between ErAs and GaAs, the Schottky barrier height between textured ErAs and n-GaAs can be reduced from similar to 0.81 to similar to 0.52 eV, and the Schottky barrier height between ErAs and p-GaAs can be increased from similar to 0.38 to similar to 0.63 eV. (c) 2006 American Vacuum Society.

In contrast to traditional metal-semiconductor (i.e., Schottky) junctions, molecular beam epitaxy (MBE)-grown ErAs:InAlGaAs heterojunctions have recently been shown to provide highly "engineerable" electrical rectification characteristics through the tuning of the Schottky barrier height, while maintaining the very low specific capacitance. This letter reports an approximate 10x improvement in the low-frequency noise performance by using MBE-grown ErAs as the Schottky contact instead of evaporated aluminum. The low-frequency noise power spectrum of ErAs devices has been observed to have a 1/f(1.0) frequency dependence. Constant-current bias-dependent measurements have shown a 1.8 power law dependence of the noise spectral density on dc current. (c) 2006 American Institute of Physics.

We demonstrate subpicosecond photocarrier lifetimes at 1.55 mum in GaSb/ErSb nanoparticle superlattices grown by molecular beam epitaxy. Pump-probe measurements were made with a 1.55 mum mode-locked laser in transmission geometry to determine the photocarrier lifetime. The lifetime is found to be dependent on the size of the ErSb particles, amount of ErSb, and the distance between layers of particles. Through manipulation of these three parameters the photocarrier lifetime can be tuned down to less than 300 fs, the temporal limit of our experiment. (C) 2004 American Institute of Physics.

International Symposium on Long Wavelength Infrared Detectors and Arrays: Physics and Applications, Miami Beach, Florida, USA, October 9-14, 1994, Series: Proceedings (Electrochemical Society)

Chromatophore organs are complex and unique structures responsible for the variety of body coloration patterns used by cephalopods to communicate and camouflage. They are formed by a pigment-containing cytoelastic sacculus, surrounded by muscle fibers directly innervated from the brain. Muscle contraction and relaxation are responsible for expansion and retraction of the pigment-containing cell. Their functioning depends on glutamate and Phe-Met-Arg-Phe-NH(2)-related peptides, which induce fast and slow cell expansion, respectively, and 5-hydroxytryptamine, which induces retraction. Apart from these three substances and acetylcholine, which acts presynaptically, no other neuroactive compounds have so far been found to be involved in the neuroregulation of chromatophore physiology, and the detailed signaling mechanisms are still little understood. Herein, we disclose the role of nitric oxide (NO) as mediator in one of the signaling pathways by which glutamate activates body patterning. NO and nitric-oxide synthase have been detected in pigment and muscle fibers of embryo, juvenile, and adult chromatophore organs from Sepia officinalis. NO-mediated Sepia chromatophore expansion operates at slower rate than glutamate and involves cGMP, cyclic ADP-ribose, and ryanodine receptor activation. These results demonstrate for the first time that NO is an important messenger in the long term maintenance of the body coloration patterns in Sepia.