High quality MOVPE-grown ZnS/GaAs epilayers are characterized by refle
ction, transmission and linear photoluminescence (PL) spectroscopy at
2 K. The GaAs substrate of a part of each ZnS layer is removed and the
optical properties of as-grown and etched surfaces are compared. The
splitting (caused by the thermally induced strain) of the topmost Gamm
a(8) valence band into the heavy and light-hole subbands (Delta(hl)=4
meV) and the transitions involving exciton ground and excited states a
re better seen in PL excitation spectra than in ordinary PL spectra. F
rom the analysis of the nonlinear PL and PL excitation spectra, we can
conclude the existence of biexcitons with a binding energy of about 1
0 to 12 meV under an intermediate intensity of excitation (a density o
f about 2.5x10(16) to 2.5x10(17) e-h excited pairs per cm(3)).