The ZnSe epilayers were grown on the GaAs substrate by hot wall epitaxy. After the ZnSe epilayers were treated in the vacuum, Zn- and Se-atmosphere, respectively. the defects of the epilayer were investigated by means of low-temperature photoluminescence measurement. The dominant peaks at 2.7988 and 2.7937 eV obtained from the PL spectrum of the as-grown ZnSe epilayer were found to be consistent with the upper and the lower polariton peak of the exciton. I-2 (D-2, X), bounded to the neutral donor associated with the Se-vacancy. This donor-impurity binding energy was calculated to be 25.3 meV. The exciton peak, I-1(d), at 2.7812 eV was confirmed to be bound to the neutral acceptor which corresponded with the Zn-vacancy. The I-1(d) peak was dominantly observed in the ZnSe/GaAs:Se epilayer treated in the Se-atmosphere. This Se-atmosphere treatment may convert the ZnSe/GaAs:Se epilayer into the p-type. The SA peak was found to be related to a complex donor like a (V-Se-V-Zn)-V-Zn. (C) 2002 Elsevier Science B.V. All rights reserved.