We describe the molecular-beam epitaxy growth, as well as both the structural and optical characterization of a set of InAs/GaSb type-II strained-layer superlattice samples, in which the GaSb layer thickness is systematically increased. Absorbance spectroscopy measurements show well-defined features associated with transitions from the various valence subbands to the lowest conduction subband, and also a significant blueshift of the band edge when the GaSb layers thickness is increased. Empirical pseudopotential method calculations are shown to successfully predict the blueshift and help identify the higher-energy transitions.

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Articles you may be interested inStudies of reactions of importance in the stratosphere. V. Rate constants for the reactions O+NO2→NO+O2 and O+ClO→Cl+O2 at 298 K J. Chem. Phys. 81, 3922 (1984); 10.1063/1.448185 Studies of reactions of importance in the stratosphere. IV. Rate constant for the reaction Cl+HOCl→HCl+ClO over the temperature range 243-365 K J. Chem. Phys. 74, 545 (1981); 10.1063/1.440807The temperature dependence of the NO-O chemiluminous recombination. The RMC mechanismThe reactions of two free radicals, nitrogen dioxide and chlorine monoxide, with oxygen atoms, 0 + N0 2 -NO + O 2 and 0 + CI~1 + O 2 , have been investigated in a fast flow system over the temperature range 220-387 K, at a total pressure of 2.3 Torr. Reaction rates were measured under psuedo-first-order conditions with either CIO or N0 2 in large excess and the decay of oxygen atoms monitored by adding nitric oxide at the end of the flow tube and detecting the 0 + NO + M chemiluminescence. The reactions are of interest, because they are thought to be the rate determining steps in two catalytic chains which destroy odd oxygen (0 and 0 3 ) in the stratosphere. Measurements of the rate constants over the stated temperature interval yielded the Arrhenius expressions ko+ N0 2 = (6.58 ± 0.52) X 10-12 ~p[ (142 ± 23)/ T] and k O + C10 = (2.61 ± 0.60) X 10-11 exp[(97 ± 64)/T]. Thus, both reactions display small negative activation energies. In addition, experiments showed no pressure effect on the reaction rate in the range 2.3-5.3 Torr and at a temperature of 230 K. Addition of a partial pressure of 1 Torr of oxygen also had no effect on the rate constant at 230 K, suggesting that CIO • O 2 formation is of little or no significance under stratospheric conditions.

We report on optically pumped semiconductor lasers emitting near 3.8 μm that exhibit high power and low output divergence. The lasers incorporate multiple InAs/InGaSb/InAs type-II wells imbedded in an InGaAsSb waveguide that is designed to absorb the pump emission. When operated at 85 K, 0.25 mm×2.5 mm broad area devices produce >5 W of peak power under long pulse conditions. Moreover, these extremely bright devices exhibit a fast axis divergence of only ∼15° full width at half maximum (FWHM), coupled with a slow axis divergence of ∼6° FWHM. The first is due to the reduced optical confinement in the transverse direction, while the latter is attributed to the suppression of filament formation, which is another beneficial consequence of the low optical confinement.