Thin nanocrystalline semiconductor films are promising materials for gas sensor applications since in such layers the sensing surface is significantly larger than the geometric one. Therefore layer resistence may show significant changes upon exposure to some gases or vapours. In this study a series of ZnSe single layers were deposited on c-Si and glass substrates at room substrate temperature. Thermal evaporation of ZnSe powder in vacuum has been performed and the layer thickness of the produced films varied between 30 and 100 nm. Also, SiO_x/ZnSe periodic multilayers have been studied. Both kinds of layers (2 or 4 nm thick) were produced using the same deposition technique. Up to four maxima have been observed in the Raman spectra of all samples taken at 20 and 295 K, using the 442 nm (2.8 eV) line of a He-Cd laser as an excitation source. The observed spectral features have been related to multiple phonon (1LO to 4LO) light scattering and connected with the existence of crystalline ZnSe grains in both single layers and the ZnSe layers of multilayers. On the other hand, absorption results imply presence of amorphous ZnSe phase in the single layers, as well. Therefore, it has been assumed that as-deposited single layers contain two phases, amorphous and crystalline. In an attempt to improve the film crystallinity, series of Raman spectra have been obtained at 295 K on both ZnSe single layers and SiOx/ZnSe multilayers using the 488 nm line of an Ar⁺/Kr⁺ laser with a gradually increased laser beam power. The obtained results indicate an increased crystallinity at high illumination levels. The effect is better pronounced in the multilayers.

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