Spin-orbit interaction, triplet lifetime, and fine-structure splitting of excitons in highly porous silicon

We present a theoretical treatment of the spin-orbit interaction in luminescent porous silicon. We calculate the radiative lifetime of the triplet exciton, which is determined by the spin-orbit interaction, and compare the results with experiment. We discuss previous work on the optically detected magnetic resonance (ODMR) of porous silicon. We show that the spin-orbit interaction causes a substantial fine-structure broadening of the ODMR. Other workers have argued that the large linewidth of the triplet ODMR cannot be explained within the quantum-confinement theory of porous silicon. Our results demonstrate that this argument is incorrect.