Unrelaxed State in Epitaxial Heterostructures Based on Lead Selenide

Abstract

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

High Deformations in Lead Selenide Nanolayers and Related New Properties

“…At the same time, at a certain growth rate, the minimal thickness of the layer for the maximum lattice constant can somewhat change with an increase in the density of dislocations in the substrate up to more than 10 6 cm -2 . 16,17 It is noteworthy that the increase in the tangential lattice constant is associated with tensile strain in the layers, and not with the difference between thermal expansion coefficients of the KCl and the PbSe layers, when, on the contrary, the lattice constant of layers decreases. The increase in the lattice constant of layers is connected with the deformations formed at the substrate-layer interface, and not at the boundaries of subgrainsin this case, disorientation is minimal and makes up one hundred-thousandth of a minute.…”

“…), the values of lead selenide band gap determined with varying thickness of layers from 4 μm to 70nm varied from 0.286 to 0.465 eV. 2,25 When the texture of the tetragonal phase appears in the X-ray spectrum, a new level emerges in the conduction band. Taking into account the effect of deformation on optical characteristics, in Figure 6 is shown the spectral dependence of α-αfr.car.…”

“…At the concentration of current carriers in the layer of 4•10 18 cm -3 , additional absorptiona peak in the vicinity of 0.285 eV appears in the optical spectrum. 26 The increase in the tangential lattice constant and the band gap by 0.055 Å and 0.170 eV, respectively, is an important illustration of the achievement of high deformations, i.e., supercriticity and high "negative" pressure in the layers up to ~10 kbar (with the elastic modulus of 5•10 11 dyn cm -2 ).…”

“…11 The concentration of current carriers and their mobility at 77 and 300 K were determined by four-probe method. 12,13…”

Epitaxial Lead Selenide Layers over a Wide Range of Their Thickness on Dielectric Substrates

“…This allowed both improving the characteristics of photodetectors and obtaining the laser structures of high quality [3]. The investigation of lead selenide grown on KCl and BaF 2 substrates revealed the possibility of creating the dielectric state under the conditions of effective "negative" pressure and appropriate doping [4]. Under certain doping, it is also possible to improve the sensitivity in the layers grown on, for instance, the NaCl substrate under the conditions of their compression.…”