S P Zimin

Micromasking effect and nanostructure self-formation on the surface of lead chalcogenide epitaxial films on Si substrates during argon plasma treatment

The surface modification of lead chalcogenide epitaxial films during plasma treatment processes is investigated. With AFM and SIMS measurements it was shown that the mechanism of a microhillock formation is the micromasking effect of dislocation exit sites. Micromasking, and hence microhillock formation, takes place when fluorine sputtered from reactor chamber walls is present on the surface of the films. Micromasks are nucleated at the exits of threading dislocations when low-volatile fluoride compounds are formed due to the reaction of atomic fluorine with Al or Pb accumulated in these areas. The effects obtained are analysed from the standpoint of nanostructure formation, which requires, primarily, the suppression of the micromasking effect. A novel method of fabricating lead chalcogenide nanostructures on Si(1 1 1) substrates via Ar plasma treatment is proposed.

Growth and properties of PbTe films on porous silicon

Abstract The structural and electrical characteristics of vacuum deposited PbTe films on Si substrate with buffer porous silicon (PS) layer were investigated. Auger electron spectroscopy, electron and optical microscopy data have shown the absence of cracks, pores, metal and chalcogen microinclusions. A mosaic structure with a grain size of 20–60 μm was detected by selective chemical etching and acoustic microscopy methods. The investigations of X-ray diffraction and X-ray pole figures showed that grains have [100] orientation along the growth direction. The cooling–heating (300–77–300 K) cycles of multilayer PbTe/sublayer/Si structures did not lead to the processes of peeling or appearance of cracks. It was found that thick amorphous layers on a PS surface change the nature of PbTe films growth.

Investigations of nanocrystalline SnS films' surface morphology modification during inductively coupled argon plasma sputtering

In this work the investigations of the morphology, structure and chemical composition of nanocrystalline SnS films grown by hot wall deposition method on glass substrates before and after high-density low-pressure inductively coupled argon plasma sputtering were performed using scanning electron microscopy, x-ray diffraction analysis, Raman spectroscopy, and energy-dispersive x-ray spectroscopy. The phenomenon of the surface smoothing for the SnS films with petal-like nanocrystallites during plasma treatment is described and the low sputtering rate for the studied films is discussed.

RF sputtering of epitaxial lead chalcogenide films in argon and krypton plasma

The measurements of sputtering etch rates for monocrystalline (111)-oriented epitaxial films of semiconductor binary compounds PbTe, PbSe, PbS in RF high-density low-pressure inductively coupled argon and krypton plasma were performed. Films with 1‐5 μm thickness were grown on Si(111) and BaF2(111) substrates using molecular beam epitaxy. Sputtering was carried out with the energy of Ar + and Kr + ions of 20‐400 eV. The sputtering etch rates of the binary lead chalcogenides are demonstrated to have abnormally high values in comparison with the basic semiconductor materials of microelectronics. The sputtering yield values for PbTe, PbSe, PbS for the average energy of the argon ions of 200 eV are practically equal (0.46 ± 0.05 molecule/ion) and vary linearly with the variation of the ion energy. Substitution of the plasma discharge gas from the argon to krypton does not result in a significant change in the sputtering yield of lead chalcogenides. The physical principles of the observed phenomena are discussed.

Formation of porous nanostructured lead telluride films by an anodic electrochemical etching method

Comprehensive research of the structural, optical and electrical properties of a PbTe/CaF2/Si(1 1 1) epitaxial system after anodic electrochemical treatment in a Norr solution electrolyte with a low current density of 6 mA cm−2 was carried out. It is shown that the anodizing results in the increase of the band gap and resistivity and in the decrease of the refractive index of lead telluride. Using secondary ion mass spectrometry, a specific change of the C, K, H element distribution in depth of PbTe films after electrochemical treatment was detected. It is demonstrated that the set of presented experimental results can be explained from the standpoint of the formation of a mesoporous structure of lead telluride with a porosity value of about 50%. The effective radius of PbTe nanoparticles is equal to 13 nm. Triple-crystal x-ray diffractometry results analysis showed that the pores have spherical voids with an average dimension of 40 nm.

Structural properties of Pb1−xEuxSe/CaF2/Si (1 1 1)

X-ray, Auger-electron spectroscopy, scanning electron microscopy and atomic force microscopy investigations of the Pb1−xEuxSe film structure with variation of x from 0.00 to 0.16 were carried out. The 2–4 µm thick films were grown on Si (1 1 1) substrates with a CaF2 buffer layer by molecular beam epitaxy. We show that the films have a high structural perfection degree for all x values. Triangular terraces and exit pits of threading dislocations were found on the film surfaces. The x-ray peaks of CaF2 (1 1 1) and Si (1 1 1) are distinguished and correlated with the Eu penetration into the volume of the thin buffer layer. A tensile in-plane strain eII in the Pb1−xEuxSe films is calculated to be equal to 0.15%–0.24%. The microstrain value e in the Si near-surface layers was found to be equal to (4.2 ± 1.0) × 10−5. The surface morphology of the films changes after high-density inductively coupled argon plasma processing is described. The role of threading dislocations and terraces on the morphology modification of the surface during plasma treatment is shown.

Investigations of the pore formation in the lead selenide films using glacial acetic acid- and nitric acid-based electrolyte

We report a novel synthesis of porous PbSe layers on Si substrates by anodic electrochemical treatment of PbSe/CaF2/Si(111) epitaxial structures in an electrolyte solution based on glacial acetic acid and nitric acid. Electron microscopy, X-ray diffractometry, and local chemical microanalysis investigation results for the porous layers are presented. Average size of the synthesized mesopores with approximately 1010 cm−2 surface density was determined to be 22 nm. The observed phenomenon of the active selenium redeposition on the mesopore walls during anodic treatment is discussed.

Fabrication of porous nanostructured lead chalcogenide semiconductors for modern thermoelectric and optoelectronic applications

Porous structures of lead chalcogenides with porosities of 20-68% and pore dimensions as small as 7-20 nm were fabricated using an anodic electrochemical etching technique applied to epitaxial PbTe and PbSe films on Si. Anodized lead selenide demonstrated two basic types of porous morphology: quasiporous noncontinuous layers and hierarchical porous layers. Lead telluride had a more typical mesoporous morphology, with pores propagating at an angle of 35° to surface, which corresponds to the <100< directions in the epitaxial films and is promising for the fabrication of photonic crystals with Yablonovite-like structure. The sizes of PbTe nanocrystallites in porous layers with high porosity were calculated to be 26 nm, which indicates that quantum confinement conditions are realized in this material. Such low-dimensional morphology of porous lead telluride is prospective for the fabrication of microscale thermoelectric devices with high ZT.

Features of the plasma sputtering of polycrystalline Pb1 − xSnxS films

The processes of the sputtering and modification of surfaces of polycrystalline films of the ternary solid solution Pb1 − xSnxS (x = 0.9–1.0) in a high-density Ar plasma of high-frequency low-pressure inductive discharge are studied. Films with thicknesses of 1–4 μm are grown on glass substrates using the “hot-wall” method and consist of plate-like crystallites. It is established that the sputtering rate for lead-tin sulfide films does not exceed 2.0 nm/s, which is determined by the presence of oxygen-containing compounds on the surfaces. In the case of plate-like crystallites with nanodimensional thicknesses, the effect of smoothing of the developed surfaces of the polycrystalline Pb1 − xSnxS layers during plasma treatment is observed; this is important for fabricating multilayer device structures.

Investigations of the inductively coupled argon plasma sputtering of Pb1 − xSnxTe ternary solid solution

Investigations of the sputtering of films of the Pb1 − xSnxTe ternary solid solution with 0 ≤ x ≤ 1 in RF high-density low-pressure inductively coupled argon plasma have been performed. The effect of a constant sputtering rate with variation in the composition of the semiconductor solid solution for (111)-oriented films with x < 0.6 and of a sputtering rate decrease with the appearance of (100)-oriented crystallites at x > 0.6 is found. The results are analyzed in the context of a model of ternary alloy sputtering based on the Sigmund solid sputtering theory when taking into account the sublimation energies of binary compounds that constitute a solid solution.