Indirect recombination mechanisms in germanium

The complete set of luminescence replicas arising from exciton recombination with the emission of a single phonon in pure germanium has been detected and analyzed. The newly resolved LO luminescence replica is found to be more intense than the TA replica and to have the same forbidden line shape. The TO line is found to have both allowed and forbidden components. These observations are in agreement with an analysis using selection rules calculated within the double-group representation necessary for germanium. The recombination mechanisms, when applied to the unresolved LA-LO or TA replicas of the e-h liquid, yield estimates of the ground-state Fermi energy and e-h pair density that are lower than previous values.