Excitons and Resonant Raman Scattering in Epitaxial ZnS Films

Abstract

Exciton lines and Raman scattering lines appearing at band edge region of epitaxial ZnS films were investigated under tunable picosecond light pulse excitations. The decay times of excitons bound to neutral donors (I₂ line) and acceptors (I₁ line) at low temperatures were measured for the first time with the use of a streak camera. The decay times of the I₁ and I₂ lines were found to be -190 ps and 40-60 ps, respectively. These decay times were compared with calculations based on the giant oscillator strength model and Sanders-Chang's theory. Under tunable (3.7-3.9eV) picosecond light pulse excitations, resonant enhancements of Raman scattering intensities were observed for LO-, 2LO-, 3LO-, TO- and LO+TO-phonon lines. The dependence of two LO-phonon Raman line intensity on excitation photon energy showed resonant enhancements with the free exciton state.