Quantum efficiency of exciton luminescence in low-dimensional structures with indirect energy gap

A theoretical model is proposed, which allows to evaluate the efficiency of the exciton luminescence in semiconductor nanostructures (NSs). Calculations have been made for Si-SiOx quantum structures with account of image potentials and finite barriers for electrons and holes, the barrier heights being functions of the content parameter x. Within effective mass and parabolic dispersion law approximations a relationship between concentrations of electron-hole pairs and excitons in quantum layers (QL) and quantum wires (QW) has been evaluated. The relationship depends on the intensity of pumping, temperature and exciton binding energy Ex which in turn is a function of NS width d. It is shown, that in the case of high barriers the internal quantum efficiency of the exciton luminescence in extremely narrow NSs (d approximate to 1 nm) can achieve almost 100% even at room temperatures. In NSs with lower barriers the exciton luminescence achieves maximal intensities at larger widths, but absolute values of the intensities are lower than those in the case of high barriers. (C) 2002 Elsevier Science B.V. All rights reserved.