E.P. Domashevskaya

XPS, USXS and PLS investigations of porous silicon

Abstract X-ray photoelectron spectra (XPS) as well as ultrasoft X-ray spectra (USXS) of porous silicon have been investigated. The samples were obtained by electrochemical etching of silicon plates in an alchohol solution of HF. Silicon 2p core states and Si L 2.3 spectra of ‘as-obtained’ samples as well as those annealed in the atmosphere were obtained. All the samples show an increase of oxidation in porous layers with temperature. However, the degree of oxidation in the sample annealed at high temperatures for 20 sec is less than that annealed for 20 min at lower temperatures.

Vegard’s law and superstructural phases in AlxGa1−xAs/GaAs(100) epitaxial heterostructures

The lattice constants of AlxGa1−x As epitaxial alloys with various AlAs (x) contents are determined for AlxGa1−xAs/GaAs(100) heterostructures grown by MOC-hydride epitaxy using X-ray diffractometry and an X-ray back-reflection method. An ordered AlGaAs2 (superstructural) phase is found in epitaxial heterostructures with x ≈ 0.50. The lattice constant of this phase is smaller than the lattice constants of an Al0.50Ga0.50As alloy and GaAs single-crystal substrate.

Influence of water vapor adsorption on the C-V characteristics of heterostructures containing porous silicon

Porous silicon (por-Si) is prepared by the electrochemical etching of single-crystal n-silicon in an aqueous-alcoholic solution of hydrofluoric acid in the presence of hydrogen peroxide oxidizer. The dependence of the high-frequency C-V characteristics of Al/por-Si/Si heterostructures on the relative humidity is studied. A model of capacitor structure is proposed, and a method of analyzing its capacitance as a function of the water vapor partial pressure in terms of the adsorption isotherm is elaborated. Within the framework of this model, the porosity of the material, the effective fraction of silicon dioxide in the por-Si, the fraction of intercommunicating porosity, the micropore-to-mesopore volume ratio, and the mesopore size distribution are determined. The porous silicon prepared in this work seems promising as a sensitive layer in capacitance-type humidity sensors.

Infrared reflectance spectra and morphologic features of the surface of epitaxial AlxGa1−xAs/GaAs(100) heterostructures with the ordered AlGaAs2 phase

The infrared reflectance spectra associated with lattice vibrations in the epitaxial AlxGa1−xAs/GaAs(100) heterostructures with different Al content in the cation sublattice are studied. The structures are grown by metal-organic chemical vapor deposition. In the spectrum of the structure with x ≈ 0.50, the vibration modes corresponding to the superstructurally ordered AlGaAs2 phase are detected. The atomic force microscopy of the surface of the sample with x ≈ 0.50 reveals areas of ordered nano-scaled profile, with a period of ∼ 115 nm. The ordered domains involve the AlGaAs2 structured phase.

Optical properties of SnO2−x nanolayers

Specific features in the optical absorption spectra and capacitance-voltage characteristics of SnO2−x nanolayers have been observed. These features are determined by the surface and intergranular states of Sn2+ ions, which appear due to the oxygen deficit and form localized states in the bandgap of SnO2−x. The observed dimensional effect in SnO2−x nanolayers is manifested by an increase in their bandgap width as compared to that in the bulk SnO2.

Synchrotron investigations of the electron structure of silicon nanocrystals in a SiO2 matrix

Silicon ions are implanted into silicon oxide thin films obtained by the thermal oxidation of silicon wafers in wet oxygen. The implantation dose is accumulated either once or cyclically, and the samples are annealed in dry nitrogen every time after implantation. The second series of samples is prepared in a similar way, but the technology for obtaining the oxide films includes additional annealing at 1100°C in air for three hours. X-ray absorption near-edge structure (XANES) spectra are obtained using synchrotron radiation. In all the Si L2,3 spectra, two absorption edges are observed, the first corresponding to elemental silicon, and the second corresponding to the SiO2 matrix. The fine structure of the first edge indicates that nanocrystalline silicon (nc-Si) can form in the SiO2 matrix, whose atomic and electronic structure depends on the technology of its formation. In both series, the cyclic accumulation of the total dose (Φ = 1017 cm−2) and the annealing time (2 h) gives rise to the most pronounced fine structure in the region of the absorption edge of elemental silicon. The probability of forming silicon nanocrystals decreases for the denser silicon oxide in the second series of samples.

ELECTRON STRUCTURE INVESTIGATIONS OF InGaP/GaAs(100) HETEROSTRUCTURES WITH InP QUANTUM DOTS

Ultrasoft X-ray emission spectra (USXES) and X-ray absorption near-edge structure (XANES) spectra with the use of synchrotron radiation in the range of P L2,3-edges were obtained for the first time for nanostructures with InP quantum dots grown on GaAs 〈100〉 substrates by vapor-phase epitaxy from metal–organic compounds. These spectra represent local partial density of states in the valence and conduction bands. The additional XANES peak is detected; its intensity depends on the number of monolayers forming quantum dots. Assumptions are made on the band-to-band origin of luminescence spectra in the studied nanostructures.