A single equation describes excitonic absorption spectra in allquantum-sized semiconductors

The relative motion of the electron-hole pairs which constitute Wannier-Mott excitons in semiconductor quantum wells, superlattices, and quantum wires can never be considered strictly 1-D, 2-D, or 3-D. We propose an exact generalization of the well-known calculations of Elliott in the 3-dimensional case, and of Shinada and Sugano for 2-dimensional media-we calculate the absorption spectrum by bound and unbound excitonic states, by using a metric space with a noninteger dimension α>1. Whatever the dimensionality, i.e., for any quantum-sized structure, the whole optical density spectrum is obtained from a single compact equation, in excellent agreement with experimental data and with the most accurate available theories. We present examples of calculated spectra for quantum wells under applied perpendicular electric fields, and for quantum wires     

Antibiotic resistance pattern of motile aeromonads from farm raised fresh water fish

Motile aeromonads isolated from the intestines of farm-raised freshwater fish such as Catla catla, Labeo rohita and Ctenopharyngodon idella have been characterized to species level. Morphological and physiological grouping revealed 61% Aeromonas hydrophila, 30% Aeromonas caviae, 7% Aeromonas sobria and 2% which remained unidentified. Hemolytic activity was detected mostly in A. hydrophila, while only half of the A. sobria and A. caviae showed this activity. Antibiotic resistance patterns of the strains revealed that they had acquired a relatively higher resistance to oxytetracycline, amoxycillin, ampicillin, novobiocin and polymixin-B, implicating possible use of these antibiotics in the aquaculture systems.     

Optical gain calculation of mid-infrared InAsN/GaSb quantum-well laser for tunable absorption spectroscopy applications

We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm^− 2, the theoretical laser structure performances reveal a gain value at around 1000 cm^− 1 at 300 K, inducing a modal gain value equal to 50 cm^− 1. Low radiative current densities lower than 100 A/cm² are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density.     

Coulomb interaction of electron gas in MQWs Si/Si1 − xGex/Si

We present a theoretical analysis of the conduction and valence-band diagrams of SiGe/Si Multiple Quantum Wells (MQWs), having a specific “W” geometry, and designed for emission or photodetection around the 1.55 μm wavelength. Peculiar features have been extrapolated by solving self-consistent Schrödinger and Poisson equations, taking into account the electrostatic attraction induced by carrier injection. As a result, Coulomb interaction strongly modifies the band profiles and increases the electron probability density at the quantum well interfaces; the injected carrier concentration enhances electron–hole wave functions overlap and the in-plane oscillator strength. These MQWs structures, strain-compensated on relaxed Si_0.75Ge_0.25 pseudo-substrates, are potentially interesting for telecom applications.     

III–V nitrides: wurtzite symmetry and optical absorption

We report here on the study of the theoretical optical properties of Ga based nitrides systems. The dipolar matrix elements and hole effective masses are presented as a function of the reciprocal wavevector for strained bulk GaN. We compute then the A, B and C exciton binding energies for strained GaN/Al_0.2Ga_0.8N quantum structures and present the calculated optical density for a 50 Å wide well.     

Electrochemical reduction of 1,2-vinylene and 1,4-butadienylene bis-phosphonium salts

The electrochemical reduction of 1,2-vinylene and 1,4-butadienylene bis-phosphonium salts has been investigated on a mercury cathode in unbuffured or acidic hydroorganic media. It is controlled by ylid character of the radical obtained after the first electronic transfer. This ylid character induces an heterolytic PC bond breaking with the unsaturated bridge. This result parallels those obtained in the chemical reduction of the same structures and confirms the high fragility of the bridge.     

Ensembles presque periodiques k-reconnaissables

We characterize the automata which recognize almost periodic sets of written in k basis integral numbers.     

Dark Current and Noise Measurements of an InAs/GaSb Superlattice Photodiode Operating in the Midwave Infrared Domain

A midwave infrared pin photodiode based on a type?II InAs/GaSb superlattice (SL) was fabricated, and electrical measurements under dark conditions were performed as a function of temperature. The SL structure exhibits photoluminescence emission at 4.55?μm at 77?K. Deduced from current density–voltage (J–V) measurements, a zero-bias resistance–area product R ₀ A greater than 1?×?10⁶?Ω?cm² at 77?K was measured. Additional noise measurements show no presence of intrinsic 1/f noise above 20?Hz, and the photodiode presents Schottky-limited behavior below ?600?mV. All these results confirm the potential for such SL InAs/GaSb superlattice pin photodiodes operating in the midwave infrared domain.