Magnetic relaxation in one-dimensional exchange-coupled (CH^NMnC^ is found to be dramatically different than it is in three-dimensional exchange-narrowed paramagnets. A theory which accounts properly for the special long-time persistence of spin-correlation functions in one dimension is shown to explain the observed behavior.

We carry out a detailed study of catastrophic degradation (CD) in DH laser material from which we reach two conclusions. First, local melting occurs and is due to intense nonradiative recombination of minority carriers at a cleaved surface or at a defect. The minority carriers are generated by absorbed superradiant light. Second, the dark line associated with CD results from propagation of a molten zone confined to the active layer. It is recrystallized epitaxially after the laser pulse but remains highly nonradiative because large numbers of point defects and dislocation loops are quenched into this region during rapid cooling from the molten state. Catastrophic damage was induced by exciting superradiance in the DH material with a cavity-dumped Ar-ion laser. The melting and recrystallization were established by observing a redistribution of Ga and Al in the x=0.08 active layers by TEM studies. The point defects were detected by scanning junction photocurrent measurements, electron-beam-induced current, and cathodoluminescent analysis. Calculations of the power required for thermal runaway at a cleaved surface, melting, and propagation of a molten zone are within twice the observed threshold intensities.

Articles you may be interested inInfluence of structural defects on carrier recombination and current gain in an InGaAs/AlGaAs/GaAs heterojunction phototransistor Emitter composition and geometry related surface recombination current of AlGaAs/GaAs heterojunction bipolar transistors Mesa surface recombination current in AlGaAs/GaAs heterojunction bipolar transistors with an emitter-base-emitter structure Effect of oxygenimplant isolation on the recombination leakage current of np + AlGaAs graded heterojunction diodes Appl.We show that the 2kT current in double-heterostructure AlxGal_xAs p-n junctions is primarily due to surface recombination at the junction perimeter. The rate of surface recombination is evaluated by means of two luminescence experiments. Both experiments provide evidence that the rate of surface recombination increases with bias as exp( e V /2 kT) and has the correct magnitude to account for the measured I· V curves. It is shown theoretically that recombination at a depleted surface is proportional to exp( e V /2 kT) at high bias. The 2 kT behavior is a consequence of the nearly constant ratio of electron and hole densities at the surface. The nearly constant ratio is needed to maintain equality of surface and surface depletion layer charge. p -n junction perimeters of cleaved, etched, and proton-bombarded interfaces are evaluated and found to have similar rates of non radiative recombination with the rate of surface recombination given by R = so(np)1I2, where So is approximately 4X 10 5 cm/sec.

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A new method for measuring absorption and gain spectra of lasers is presented. These spectra are deduced from measurements of spontaneous emission spectra at different laser currents supplemented by measurements of the laser line energy and the differential quantum efficiency. The spontaneous emission emerged from the side of the laser after traveling through a transparent cladding layer. At each current, the bias energy eV is determined. A simple theoretical model is used to convert eV to minority carrier density. The method is based on the application of general relations between the rates of spontaneous emission, stimulated emission, and optical absorption. A new general proof of these relations is presented. The gain versus carrier density relation at the laser line energy is measured for four samples having different active layer doping or Al composition. Gain increased superlinearly with carrier density in undoped and n-type samples and increased slightly sublinearly in a p-type sample. The losses at low carrier densities ranged from 100–200 cm−1. For one undoped sample, the changes in the absorption edge caused by the electron and hole densities increasing from 5×1016 to 1.1×1018 cm−3 were deduced by comparing the measured changes with a model calculation. It was found that the exponential broadening increased 20%, that the energy gap decreased 12–16 meV, and that the strength of optical absorption at low energies decreased by about a factor of 1.4.