Lithium-doped p-type ZnS epitaxial layers have been grown on (0 0 1)-oriented GaAs substrates by low-pressure metalorganic chemical vapor deposition using tertiarybutyllithium as an acceptor dopant source. As-grown samples exhibited electrically high resistive n-type or p-type conductivity. However, all samples exhibited p-type conductivity after annealing in N-2 atmosphere at 550degreesC. The highest net acceptor concentration (N-A - N-D) was estimated to be about 4.1 x 10(16) cm(-3). Photoluminescence (PL) spectra of lithium-doped ZnS epitaxial layers with N-A - N-D < 10(15) cm(-3) were dominated by the radiative recombination of excitons bound to a lithium acceptor at 327.6 run. On the other hand, PL spectra of lithium-doped ZnS epitaxial layers with N-A - N-D > 10(15) cm(-3) were dominated by free-to-acceptor emission with LO phonon replicas. From the peak energy of the FA emission, the lithium acceptor ionization energy was estimated to be about 196 meV. (C) 2002 Elsevier Science B.V. All rights reserved.