Bound-exciton absorption in Si:Al, Si:Ga, and Si:In

We present high-resolution measurements of bound-exciton absorption for Si:Al, Si:Ga, and Si:In. In each case we observe at least three absorption lines due to the ground state and two excited states of the bound exciton. By comparing the measured no-phonon oscillator strengths for the three absorption lines with calculations of these quantities we establish that the triplet structure results from hole-hole coupling in the crystal field. We assign symmetry labels to the three states based on the observed oscillator strengths. We observed a small valley-orbit splitting of the lowest-energy line in Si:Al and absorption due to two highly excited states of the bound exciton in Si:In.