Far-infrared magnetoabsorption of exciton system in silicon

In this work we report on the first observation of the far-infrared laser (84-220 {μ}m) magneto-optical absorption by the exciton system in silicon up to the magnetic field of 50 kG and over the temperature range of 1.7-50 K. The major absorption lines observed for three geometries, →B∥〈001〉, →B∥〈111〉, and →B∥〈110〉, are safely attributed to the 1s→2p-type transition of excitons. It is found that the absorption linewidth is sensitive to temperature and to impurity concentration. The magnitudes of the exciton-phonon interaction and of the exciton-impurity interaction are thereby discussed. The absorption increases markedly with temperature and increases linearly with the level of excitation, indicating the coexistence with electron-hole drops. The work function of the condensed phase is obtained through the thermodynamical method to be φ=7.6 meV. From the time-resolved experiments, the temperature dependence of the lifetime of the exciton is also obtained.