The density of ZnS thin films is determined as a function of the film thickness. The films were prepared using atomic layer epitaxy. Two experimental techniques are used, namely, (1) spectroscopic ellipsometry combined with Hehyphen;ion backscattering spectrometry and (2) spectroscopic ellipsometry alone using an effective medium approximation. Both methods give approximately the same results. In the ZnS thin films having a cubic crystal structure, the mean density increases from about 2.5 to about 4.0 g/cm3with increasing film thickness in the thickness range of 25ndash;400 nm. In the films thicker than 500 nm the density starts to decrease from the value 4.0 g/cm3. In the thickness range of 1000ndash;2000 nm the density is 3.7ndash;3.8 g/cm3. When the distance from the substrate is between 50 and 300ndash;400 nm the local density of the cubic thin films has a maximum value which is close to the bulk density 4.1 g/cm3. The stoichiometric atomic ratio of sulfur to zinc is found to be between 0.9 and 1.0. The ratio has a tendency to increase with increasing film thickness.
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