Resonance Raman studies in Cu2O. I. The phonon-assisted 1 s yellow excitonic absorption edge

Abstract

Resonant Raman scattering in Cu2O has been studied at low temperature in the vicinity of its phonon-assisted 1 s yellow excitonic absorption edges using a cw continuously tunable dye laser. The multiphonon Raman modes which show resonance enhancement in this region are the following: 12-+P (where P is an odd-parity optical phonon); 212-+P (where P is an acoustic or odd-parity optical phonon); 212-+2LA and 412-. The Raman cross sections of these modes have been calculated using perturbation theory. To explain the dispersion in the experimental cross section it was found necessary to introduce a wave-vector-dependent damping constant for the 1s yellow exciton. A simple model proposed earlier by Yu, Shen, Petroff, and Falicov was used to calculate this damping constant. Our result showed that the damping is predominantly due to intraband scattering via the longitudinal acoustic (LA) phonon. Good agreement was found between experiment and theory. Our results also indicate that the resonant three- and four-phonon Raman processes in Cu2O in this region involve cascading of the photoexcited 1 s yellow exciton with emission of phonon(s). The Raman frequencies of some of the modes of Cu2O were found to depend on the incident laser frequency. The behavior of these dispersive Raman modes was found to be well explained within the above model and enabled us to determine directly the effective mass of the 1 s exciton to be (3.00.2)m0 (where m0 is the free mass of the electron), as previously reported. Relative magnitudes of various 1 s exciton-phonon interactions have also been obtained from our result. © 1975 The American Physical Society.