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The electrical performances of III-nitride blue micro-light-emitting diodes ( µLEDs) with different tunnel junction (TJ) epitaxial architectures grown by metalorganic chemical vapor deposition are investigated. A new TJ structure that employs AlGaN is introduced. The current density–voltage characteristic is improved by incorporating AlGaN layer above the n-side of the TJ layer, and the effects of the AlGaN/GaN superlattices is examined. Based upon the data from band diagram simulation, net positive polarization charge is formed at the AlGaN/GaN interface, which results in a reduction in tunneling distance and increase in tunneling probability. Moreover, similar electrical improvement is observed in various device dimensions and is independent of operating current density, suggesting that AlGaN/GaN biaxial tensile strain or current spreading is not the main contribution for the improvement. Finally, the effects on the efficiency performances are determined. While the maximum external quantum efficiency of the TJ devices remains identical, the wall-plug efficiency of µLEDs is enhanced significantly by the proposed AlGaN-enhanced TJ design. This work reveals the possibility of energy efficient TJ contact with high transparency in the visible wavelength range.

An in situ study of the effects of ionizing radiation on the strength of the Raman and photoluminescence signal of high OH, low OH, and fluoride core fibers has been performed with 514.5 nm laser excitation. The fibers were irradiated with a 60Co source at a constant dose rate of 560 rads/h. The high OH fiber displayed a much slower decay of the fiber Raman intensity than the other two fibers during irradiation. The fluoride fiber exhibited the quickest decline in Raman signal with the intensity dropping by a factor of 1000 in less than 20 min. The Raman intensity of the low OH silica fiber recovered to greater than 90% of its pre‐irradiation value after a post‐irradiation photoanneal with 488 nm laser light. The silica fibers displayed an increase in intensity of a broad photoluminescence feature centered at 650 nm. However the fiber photoluminescence intensity remained much weaker than the Raman intensity throughout the irradiations.

The photosensitivity of 50 and 100 μm square microdischarge devices having an inverted pyramidal Si cathode has been demonstrated and characterized in the ultraviolet, visible, and near-infrared (350–1200 nm). When operating with 500 Torr of Ne, (100 μm)2 microdischarge devices exhibit responsivities of 700±150 and 570±120 A W−1 at 850 and 660 nm, respectively, or more than an order of magnitude larger than peak values typical of commercially available Si avalanche photodiodes. Maximum sensitivity occurs in the 800–900 nm region for the larger (100 μm square) devices but is blueshifted to 600–650 nm for (50 μm)2 detectors. The peak response for the 50 μm square device is 950±250 A W−1 (at ∼625 nm), an increase of ∼35% over that for the (100 μm)2 detector. The experimental results indicate that the semiconductor photocathode determines the spectral response of the device whereas the plasma serves as an electron multiplier. The sensitivity and dynamic range of this new hybrid semiconductor/plasma photodetector suggest that arrays of microdischarge photodetectors are potentially valuable for spectroscopic and biochemical applications.

Detailed measurements of the time‐dependent electron density, xenon excited‐state densities, and total HCl depletion have been recently made in electron‐beam‐ (e‐beam‐) pumped XeCl. This paper presents the results of extensive computer modeling of these experiments and detailed comparisons with the measured results. The model used includes updated HCl reaction cross sections and an enlarged xenon excited‐state manifold. A reduced Boltzmann equation is used to calculate the high‐energy electron‐energy distribution function, and the low‐energy distribution function assumes a quasi‐Maxwellian distribution. These changes are upgrades to prior models. The model accurately predicts the total HCl depletion, the time‐dependent electron density for initial HCl concentrations ≥0.16% (4.8 Torr), and the time‐dependent xenon excited‐state densities for lean (≂0.04%) initial HCl concentration cases. The model tends to underpredict the rate of electron‐density growth after the electron density begins to run away. Since depletion of HCl is a key factor in understanding the kinetics data, possible mechanisms that can contribute to this process are also discussed.

The rare‐gas monohalides are simple diatomic molecules whose properties and emission spectra were essentially unknown as recently as four years ago. Now they are the active media for gas lasers that could provide overall electrical efficiency as high as 10%. These lasers operate in the ultraviolet and vacuum‐ultraviolet spectral regions and are the first lasers outside the infrared region that appear to be scalable to high single‐pulse energy (greater that 100 joules per pulse) with high average power and efficiency. Not surprisingly in light of the species' novelty and the laser's promised utility (for example, in photochemical‐separation schemes), research and development in this area has grown remarkably since the first laser demonstration three years ago.

Production and decay of N2(A 3Σ+u) (v=0, 1, 2) states were monitored photoelectrically from the sensitized fluorescence of NO γ bands. These states were produced by collisional transfer from excited Xe (1S4) which in turn was produced by radiative energy transfer via resonance radiation (147 nm) from a closely coupled Xe flash lamp. The rate coefficient for the deactivation of N2(A 3Σ+u) by I2 was measured as kI2= 6.9±1.9×10−12 cm3/sec. The deactivation by NO itself was measured as kNO=4.5±0.5×10−11 cm3/sec.

Time resolved measurements have been made of the room temperature decay of excited electronic states of Pb. The excited atoms were produced by photodecomposition of tetramethyl lead and the concentrations of the excited states were monitored by atomic resonance absorption. Quenching rate constants of the spin orbit states 3P2 and 3P1 were obtained for the collision partners Ar, Xe, H2, D2, N2, and O2. These results are discussed in terms of curve crossings, curve merging, chemical reaction, and E→V energy transfer processes. Comparison is made with the quenching rate constants for these states reported by Husain and Littler.

The emission spectra of XeBr, XeCl, XeF, and KrF at high pressure are reported and discussed. The spectra were obtained by observing spontaneous emission from electron beam excited mixtures of argon containing lesser amounts of xenon with the halogens or krypton with fluorine. The emitting state in these species is best described as an ionic species Xe+X− or Kr+F−. The wavelengths of these emission bands are in good agreement with a theoretical model in which the ionic binding energy of the noble gas halide ion pair is roughly equal to that of the nearest alkali halide. Our high pressure spectra imply that the lowest potential energy curve for XeF is bound.

A 25‐J, 50‐ns laser pumped by opposed electron beams is described. Experiments with this device demonstrated a 9% intrinsic laser efficiency at power deposition rates of about 1 MW/cm3. Parasitic control and narrowband output required for Raman‐compression experiments were demonstrated by injection locking the laser. Experiments showing an angle‐encoded extraction of energy from the medium (pulse stacking) with three pulses using a high‐gain three‐pass amplifier configuration are also described. The device utilizes triggering schemes of very low jitter suitable for synchronization to other components for optical pulse‐compression experiments.

Geometrical considerations are important with respect to the stability and efficiency of avalanche electric discharge lasers. Parameters such as the electrode contours and the distribution of preionization electrons affect excitation rates through the relative values of the local electric field, local depletion of initial species, and through the response of the discharge circuitry to spatially dependent conditions within the plasma. Constriction of the discharge and subsequent impedance mismatch of the discharge to the pulse forming line result from these spatial nonuniformities. In this paper geometrical effects in the mercury bromide electric discharge laser are examined by comparing the results from a multidimensional discharge and kinetics model with experimental observations. The code models electron and heavy particle kinetics and laser intensity in time and one spatial dimension: parallel to the electrodes and perpendicular to the optical axis. Quantities whose spatial dependence is perpendicular ...

The primary dissociation step for alkali halide diatomics in argon has been studied in order to determine whether collisional dissociation produces ions, atoms, or a mixture of both types of products. The method is based on time‐resolved absorption spectroscopy of shock‐heated vapors. Results show that the cesium halides, and the rubidium and potassium halides, with the exception of the two iodides, dissociate essentially completely to ions; that the lithium salts and NaI and NaBr dissociate essentially completely to atoms; and that the other alkali halides (KI, RbI, NaCl, and probably NaF) dissociate to mixtures of atoms and ions, at least under some conditions. The branching ratio of atom pairs/ion pairs is interpreted in terms of the effective width of the adiabatic dissociation channel, compared with the spacing of the vibrational levels of the diabatic bound state.

The unit of structure, space group symmetry and detailed atomic arrangement of lepidocrocite are determined from x‐ray data, and the existence and location of hydrogen bonds in the structure are established from considerations of interatomic distances. The orthorhombic lattice is end centered on (100), and has the axes a0 = 3.87A, b0 12.51A, and c0 = 3.06A. The space group is Vh17—Amam. The parameters are determined as uFe = —0.332, uO = +0.282, and uOH = +0.075. The structure is described as consisting of iron‐centered oxygen octahedra joined by the sharing of edges into two‐dimensionally infinite layers, with the successive layers held together by hydrogen bonds. The relationship between the diaspore‐goethite structure and the bohmite‐lepidocrocite structure is discussed from the standpoint of the coordination theory, and found to depend on two alternative ways of satisfying the electrostatic valence rule.

The dissociation of diatomic CsBr molecules in a shock wave has been studied by time‐resolved absorption spectroscopy. Absorption by neutral cesium atoms increases monotonically toward its equilibrium value as dissociation proceeds, but under a wide range of conditions, absorption by Br− ions goes rapidly to a maximum and then falls to its equilibrium value. The results show that under some conditions, the principal primary products of dissociation are ions, rather than atoms or a thermally equilibrated mixture of atoms and ions.

The parameters in diaspore are redetermined, and the structure is discussed from the standpoint of the coordination theory. The existence and location of hydrogen bonds in the structure are established, and representative formulas are proposed.

The molecular Zeeman effect in the following strongly nuclear coupled molecules was analyzed in magnetic fields near 20 000 G: 35ClF, 37ClF, 79BrF, 81BrF, 35Cl12C15N, 37Cl12C15N, 79Br12C15N, 81Br12C15N, and 127I12C15N. The molecular g values, the shielded nuclear g values, magnetic‐susceptibility anisotropies, and molecular quadrupole moments are determined for each of the above molecules. The isotope dependence in the molecular g values gives the electric dipole‐moment sign in −ClF+ and +ClCN−. The 127I nuclear magnetic shielding anisotropy in 127I12C15N was also determined. The known molecular structures combined with the above Zeeman data were used to determine the paramagnetic‐ and diamagnetic‐susceptibility tensor elements.

A new laser operating on the 342‐nm band of I2 is reported. Electron‐beam‐excited mixtures of argon with CF3I and HI produced this I2 laser. The excited state of this laser is probably formed by ion recombination reactions, and a plausible mechanism is given.

High efficiency x‐ray preionized discharge XeCl laser excitation has been achieved by combining spiker/sustainer excitation techniques with a simple and reliable magnetic isolator. The troublesome rail‐gap switch has been eliminated by using the laser discharge itself as the switch. An efficiency of 4% with 2.7 J optical energy was demonstrated.

This letter describes two new lasers operating on the 2Σ+1/2→2Σ+1/2 bands of XeCl (at 308 nm) and KrF (at 249 nm). Pumping was achieved by high‐intensity electron beam excitation of high‐pressure Ar containing small amounts of Xe and Cl2 or Kr and F2. An efficiency of about 0.4% was observed in the initial experiments on KrF, and higher efficiencies appear possible.

Operation of a large volume x‐ray preionized avalanche discharge mercury bromide laser is reported. Output energies in excess of 3 J have been obtained; the best efficiency is 2.1% at an output energy of 2.2 J.

Weak laser oscillation has been demonstrated on the 489‐ and 777‐nm electric‐dipole‐forbidden 1S0–3P1 and 1S0–1D2 transitions of the selenium atom. Carbonyl selenide has been photolyzed at 172 nm by Xe*2 radiation to produce the Se(1S0) excited state.

A device is described in which Xe is optically pumped (147 nm) and reacted with NF3 to form XeF. The same apparatus can be used to pump Kr and Ar and thereby form excited rare gas halides, oxides, and sulphides. The device is small, allowing repetitive pulsing and signal averaging techniques to be used.

A rotating disk mechanical shutter system has been developed to trigger flash photolysis experiments and prevent scattered light from blinding photomultipliers mounted on a monochromator. Trigger pulses are provided by He/Ne laser light passing through a pinhole in the disk. The monochromator entrance slit is exposed after a variable delay time by a slot in the disk. The system provides fast slit opening times (a few μsec), μsec jitter in delay times, and very high discrimination against unwanted light (rejecting unwanted signals ∼104 times the desired signal). The system is ideal for flash or laser photolysis experiments which must utilize very weak line sources as kinetic probes.

This letter reports laser action on the xenon monofluoride 2Σ1/2→2Σ1/2 band at 354 nm. Lasing on discrete vibrational bands has been achieved by pulse excitation of high‐pressure mixtures of F2/Xe/Ar with an electron beam. XeF is a member of a new class of diatmoic molecules, the noble gas monohalides, which all exhibit similar molecular structure and spectra, and laser action should be attainable on the various bands of other members of this class of molecules. The kinetics and loss mechanisms of these laser candidates are briefly discussed.