On the electron-phonon and exciton-phonon interaction in ZnTe

The Λ-modulated reflectance spectrum of ZnTe is investigated in the spectral region above the energy of the exciton ground state Esub(ex1). Structures are observed near the energy Esub(ex1) + hω0 (hω0 is the LO-phonon energy) and at the energy Esub(g) + 1.3 hω0 (Esub(g) is the gap energy). In accordance with similar results obtained in a lot of other II,VI compounds the first of these structures is interpreted from the point of view of the exciton-phonon complex formation. The second structure not observed experimentally so far is ascribed to a polaron effect. In order to support this interpretation the existing theory of this polaron effect is extended to the determination of the spectral dependence of the real part of the dielectric function. This allows the determination of the behaviour of the reflectance R and of the derivative dR/dΛ. The theoretical results are in quite good agreement with the experimentally observed spectrum. (author)