Electron capture in GaAs quantum wells via electron-electron and optic phonon scattering

Electron capture times in a separate confinement quantum well (QW) structure with finite electron density are calculated for electron-electron (e-e) and electron-polar optic phonon (e-pop) scattering. We find that the capture time oscillates as function of the QW width for both processes with the same period, but with very different amplitudes. For an electron density of 10^11 cm^-2 the e-e capture time is 10-1000 times larger than the e-pop capture time except for QW widths near the resonance minima, where it is only 2-3 times larger. With increasing electron density the e-e capture time decreases and near the resonance becomes smaller than the e-pop capture time. Our e-e capture time values are two-to-three orders of magnitude larger than previous results of Blom et al. [Appl. Phys. Lett. 62, 1490 (1993)]. The role of the e-e capture in QW lasers is therefore readdressed.Comment: 5 pages, standard LaTeX file + 5 PostScript figures (tarred, compressed and uuencoded) or by request from [email protected], accepted to Appl. Phys. Let

Fluidized Bed Incineration of Sewage Sludge in O₂/N₂ and O₂/CO₂ Atmospheres

Sewage sludge incineration in a fluidized bed is considered to be one of the most suitable ways of sewage sludge disposal. This process reduces the volume of the waste and causes the destruction of organic contaminants such as POPs, pharmaceuticals, and other compounds with endocrine-disrupting potential. Oxygen-enriched air combustion and oxy–fuel combustion can increase the combustion efficiency, reduce the amount of flue gas, and make possible CO₂ capture more effective. However, the influence of incineration medium composition has not yet been thoroughly investigated in the case of sewage sludge incineration. In this paper, the incineration of sewage sludge in a bubbling fluidized bed reactor was studied at oxygen-enriched air conditions, oxy–fuel conditions, and oxy–fuel conditions with zero and nonzero concentrations of steam, CO, NO, N₂O, and SO₂ in the inlet combustion medium. Consequently, the effects of various operating parameters on pollutants formation were comprehensively described with emphasis on aforementioned sewage sludge incineration processes. An increase in combustion temperature resulted in an increase in NO_<i>x</i> and SO₂ emissions and in a decrease in N₂O emissions. Increase in inlet oxygen concentration led to a decrease in NO_<i>x</i> and N₂O emissions. N₂O and SO₂ emissions were higher in CO₂-rich atmosphere (oxy–fuel combustion conditions). The presence of water vapor in the inlet combustion medium resulted mainly in the reduction of NO_<i>x</i> emissions. The presence of CO, NO, N₂O, and SO₂ in the dry inlet combustion medium reduced mainly overall nitrogen-to-NO_<i>x</i> conversion, while the effect on SO₂ removal efficiency was only marginal