Inter-Valence-Band Absorption in Electron-Hole Droplets

The broad line shape for absorption due to transitions between heavy-hole and spin-orbit bands in electron-hole droplets in Ge is explained. The calculation uses multiple-scattering concepts to remove the divergences of ordinary perturbation expansions in the dynamical Coulomb interaction. The absorption resembles the free-hole theory at low frequencies, is sensitive to both band anisotropy and screening approximations at intermediate frequencies, and is independent of screening at high frequencies.