Fine structure and temperature dependence of shallow core excitons in insulators and semiconductors

The excitonic spectra associated with the shallow core levels K(+)3p, Ga3d, and In4d in potassium halide and III-V semiconductor single crystals were studied by high resolution reflectivity (DeltaE < 10 meV) as a function of temperature down to 20 K. Analysis of the fine structure, transition energies, line profiles, halfwidths, and their temperature dependence yields information on the exciton (electron)-phonon interaction and on the influence of lattice expansion. Strong electron-phonon coupling dominates in the K(+)3p excitons as it does in F centers, whereas weak coupling describes the core excitons in semiconductors. The contributions of initial and final states are discussed. Core surface excitons in semiconductors show a significantly smaller temperature coefficient than the volume excitons.