The article deals with the peculiarities of creation of effective negative pressure and the increase in the forbidden gap width in PbSe nanolayers. The dielectric state that maybe realized under these conditions and their appropriate doping can be considered as a new resource in lead selenide nanolayers. The increasing of the tangential lattice constant with higher growth temperature and layer growth rate confirms this consideration. When determining the forbidden gap width, the optical transmission spectra were processed by a model of the Fabry-Perot interferometer, and, at high concentration of free current carriers, the absorption on them and their degeneracy were taken into consideration.

The work deals with the epitaxial PbSe layers grown on the KCl substrates by the method of “hot-wall” molecular epitaxy over the range of layer thicknesses of 20 - 2000 nm. Special emphasis is put on the values of elastic deformations that could be generated and frozen in epitaxial layers with the aim of influencing their energy spectra and optical properties. The maximum deformation at layers tension made up 57% of the initial mismatch between the layer and the substrate (ε = Δa/a = 0.015). In such a solid-state structure effective “negative” pressure is realized, which is justified by increase in the tangential lattice constant and the forbidden gap width. This width correlates with the tangential lattice constant (deformation) and corresponds to certain values of definite frequencies of direct electron transitions across the forbidden gap

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It was revealed that, according to the analysis by the half-width of the X-ray lines of reflection planes (200) and (600), the sizes of subgrains in the lead selenide nanolayer ~70 nm thick made up 30-45 nm. Disorientation between the subgrains of the order of the ten thousandth of a minute and the deformation (strain) in the layer was determined by the mismatch between the layer and the substrate. It is shown that the forbidden gap width Eg of the same PbSe nanolayer determined by analyzing the optical transmission spectra by two types of straightening f (hν) and (hν)2=f (hν) coincided and made up 0.445 eV, which exceeded Eg of the unstrained PbSe layer by 0.16 eV. The total contribution of quantum effects at the given subgrain sizes and degeneracy of current carriers is less than 0.03 eV, and generally the change in the forbidden gap width was associated with deformation. Key words: dispersion, deformation, disorientation between subgrains, optical transmission, forbidden gap width.

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