Intraexciton and intracenter terahertz radiation from doped silicon under interband photoexcitation

Terahertz photoluminescence of boron- and phosphorus-doped silicon at low temperatures under interband photoexcitation is investigated. The lines of radiative transitions between free-exciton levels and between the levels of shallow impurity centers are observed. The intensities of these lines exhibit different dependences on temperature and excitation intensity. At temperatures near the temperature of liquid helium ($T\sim 5$ K), the terahertz radiation spectrum features a broad band (about $18$–$20$ meV wide) with a peak at an energy of about $20$–$22$ meV. This band is apparently associated with radiative transitions of nonequilibrium charge carriers from the states of the continuum to the state of an electron-hole liquid.