The ZnSe/GaAs epilayers grown by hot wall epitaxy have been investigated by means of Raman, and photocurrent (PC), and photoluminescence spectroscopy. Raman spectroscopy measurement showed that a plasmon-longitudinal optical phonon-coupling mode existed together with its characteristic longitudinal optical phonon. The temperature dependence of the energy band gap of the ZnSe/GaAs epilayer was found to be E-g(T) = 2.8210 eV - (9.11 x 10(-4) eV/K)T-2/(298.1 + T) based on PC measurement. Also, the energy band gap, E-g(T), at 300 K has been determined to be 2.6839 eV. From the photoluminescence spectra, two dominant peaks of 2.7988 and 2.7937 eV separated from the free exciton peak at 442.4 nm (2.8026 eV) have been found to be associated with the upper and the lower polariton peak of the exciton, I-2 (Ddegrees, X), respectively. This polariton peak is attributed to the strain due to the lattice mismatch between the substrate and the ZnSe epilayer. On the basis of the obtained results, the donor-impurity binding energy is calculated to be 25.3 meV. (C) 2002 Elsevier Science B.V. All rights reserved.