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

Abstract

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 (ΔE < 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.