Search

Bistable devices are fundamental to digital electronics as building blocks of switches, logic gates, and memory in computer systems. We demonstrate here transistor lasers exhibiting both electrical and optical hystereses with sharp square-corner current switching and different voltage thresholds in the collector IC-VCE and optical L-VCE family of characteristics. The electro-optical hysteresis is explained by the different switching paths of electron-hole (e-h) and photon interactions involving cavity coherent and incoherent energy states employing intracavity photon-assisted tunneling at the collector junction and spontaneous/stimulated e-h recombination at the base quantum-well. The electro-optical bistability of the transistor laser possesses a unique property of voltage (field) modulation and the basis for high speed optical logic processors. [ABSTRACT FROM AUTHOR]

The electric transport properties of superconducting c-axis FeSe0.46Te0.54/Au (S/N) junctions, fabricated using pulsed laser deposition, have been investigated in the temperature range of 2 K to the superconducting transition temperature Tc (∼ 13.5 K) and in the presence of applied magnetic fields from 0 to 9 T. A large zero bias conductance peak has always been observed in every conductance spectrum of several batches of junctions. In addition, we have found several gap-like features. Using the extended BTK theory with the currently favored nodeless S±-wave symmetry, our conductance spectrum can be reproduced quite well in the low bias range with Δ1 = 4 meV and Δ2 = 6 meV at 2 K. However, the experimental conductance spectrum is substantially below the one calculated in the high bias range. Furthermore, there is a conductance minimum at approximately 20 meV, which may be the reason for the discrepancy. [ABSTRACT FROM AUTHOR]

An improved technique of convective solution transport using KCl as solvent at 840-790 °C (where mass transport takes place across a vertical temperature gradient) is described for the growth of crystals of the recently discovered superconductor α-FeSex (x = 1-0.8). The crystals were annealed in situ at 400-350 °C for 20-30 h to improve the superconducting properties. Hexagonal plate like crystals measuring 5-6 mm across and 0.25-0.5 mm thick were obtained. High resolution transmission electron microscopy (HRTEM) measurements show good crystallinity and the energy dispersive x-ray analysis (EDX) gives a composition very close to the starting powders. The zero resistance temperature of the crystals was found to increase from 6.5 to 9 K as the composition is decreased from x = 0.95 to 0.9 and decrease thereafter. Similar behavior was also observed in the powder x-ray diffraction (XRD) patterns and Raman spectra with the main peak shifting to higher value until 0.9 and decrease thereafter. In addition the XRD patterns show reducing hexagonal phase reflections as x decreases to 0.9. Anisotropic magnetic behavior was observed when the magnetic field is applied parallel and perpendicular to the (101) face. [ABSTRACT FROM AUTHOR]

Vertical microcavity surface-emitting lasers employing quantum wells and small aperture buried-oxide current and field confinement are demonstrated with wider mode spacing and faster spontaneous carrier recombination (enhanced Purcell factor), lower threshold current, larger side mode suppression ratio (SMSR), and higher photon density and temperature insensitivity. The result is a microcavity laser that achieves higher microwave modulation bandwidth (f-3dB = 15.8 GHz) at ultra-low power consumption (1.5 mW) with a slope for the modulation current efficiency factor (MCEF) = 17.47 GHz/mA-1/2, as well as a better quality eye diagram in high-speed data transmission. The microwave behavior model for the microcavity laser is used to estimate the enhanced recombination and reduced lifetime. [ABSTRACT FROM AUTHOR]

Thin Al2O3 surface-passivating layers grown by atomic layer deposition at 100 °C were demonstrated to be instrumental in producing efficient light emission from silicon. External quantum efficiency up to 1.3×10-4 was observed from silicon metal-insulator-semiconductor light-emitting diodes with a 5 nm Al2O3 surface-passivating layer as the insulator, which is more than tenfold that from similar devices with a 5 nm SiO2 insulator layer thermally oxidized at 1000 °C. Anomalous temperature dependences of the photoluminescence intensities and spectra at low temperatures indicate the presence of bound excitonic traps at the Al2O3/Si interface. The enhanced light emission may be attributed to the temporary capture of excitons by the interfacial bound excitonic traps, which effectively reduces nonradiative recombination. [ABSTRACT FROM AUTHOR]

Discusses a study on the control of the in-plane epitaxy for bi-epitaxial grain boundary junctions using a new multilayer structure. Details of the experimental procedures; Density of the junctions made on the boundary; Current-voltage characteristics of the junctions.

Reports on the activity and diffusivity of oxygen in liquid silver-Yb[sub1]Ba[sub2]Cu[sub3] and Tl[sub1]Ba[sub2]Ca[sub2]Cu[sub3] alloys. Measurements of thermodynamic and transport properties of oxygen; Diagram of a galvanic cell for experiment with the liquid alloys; Time dependence of the total cell current and the pure ionic current of the alloys.

Details a study which measured the temperature dependence of the normal state resistivity for (R[sub0.8]Pr[sub0.2])Ba[sub2]Cu[sub3]O[sub7-δ]. Experimental procedures; Information on the study sample; Influence of temperature dependence on hybridization.

Analyzes the growth of single crystals of the superconductor YBa[sub2]Cu[sub3]O[suby] from a mixture of solid phase YBa[sub2]Cu[sub3]O[suby] and liquid phase silver. Details of the process involved in growing high J[subc] superconducting yttrium (Y)-123 crystals from a mixture of stoichiometric Y-123 and Ag[sub2]; Description of stoichiometric Y-123 powder; Comparison between single and cube-like crystals; Effect of the addition of Ag[sub2]O on the stoichiometric Y-123 powder.