É. P. Domashevskaya

Temperature dependence of residual stress in epitaxial GaAs/Si(100) films determined from photoreflectance spectroscopy data

In the temperature range T=10–300 K, photoreflectance spectroscopy was used to study the temperature dependence of residual stress in epitaxial n-GaAs films (1–5 µm thick, electron concentration of 1016–1017 cm−3) grown on Si(100) substrates. A qualitative analysis showed that the photoreflectance spectra measured in the energy region of the E0 transition in GaAs had two components. They consisted of the electromodulation component caused by the valence subband |3/2; ±1/2〉-conduction band transition and the low-energy excitonic component. The magnitude of stress was determined from the value of the strain-induced energy shift of the fundamental transition from the subband |3/2; ±1/2〉 with respect to the band gap of the unstressed material E0(T)-E0|3/2; ±1/2〉(T). The increase in the energy shift E0-E0|3/2; ±1/2〉 from 22 ± 3 meV at 296 K to 29 ± 3 meV at 10 K, which was found in the experiments, gives evidence of an increase in biaxial stress with decreasing temperature.

Theoretical and experimental study of the electronic structure of tin dioxide

The electronic structure of tin dioxide has been theoretically studied within the linearized augmented plane wave method using the Wien2k program package. The total and local partial electron densities of states have been calculated. The X-ray emission K-spectrum of oxygen has been calculated. The X-ray absorption spectra of the tin M4,5-edge and oxygen K-edge have been calculated by simulating the supercell and core hole. The calculated results have been compared with the experimental data obtained using synchrotron radiation.

Interference phenomena of synchrotron radiation in TEY spectra for silicon-on-insulator structure.

The general matrix theory of the photoelectron/fluorescence excitation in anisotropic multilayer films at the total reflection condition of X-rays has been developed. In a particular case the theory has been applied to explain the oscillation structure of L(2,3) XANES spectra for a SiO(2)/Si/SiO(2)/c-Si sample in the pre-edge region which has been observed by a sample current technique at glancing angles of synchrotron radiation. Remarkably the phase of the oscillations is reversed by a ∼2° angle variation. The observed spectral features are found to be a consequence of waveguide mode creation in the middle layer of strained Si, which changes the radiation field amplitude in the top SiO(2) layer. The fit of the data required the correction of the optical constants for Si and SiO(2) near the Si L(2,3)-edges.

X-ray Spectroscopic Study of Electronic Structure of Amorphous Silicon and Silicyne

X-ray and ultrasoft X-ray spectroscopy have both been applied to study SiKβ and SiL23 emission spectra of crystalline silicon (c-Si), amorphous hydrogenated silicon (a-Si:H), and silicyne (a new allotropic linear-chain form of silicon). SiL23 spectra of silicyne show three peaks instead of two observed in crystalline and amorphous silicon. The third peak lies in the high-energy range at 95.7 eV, its intensity constituting ∼75% of that of the main peak. An additional peak is also observed in the short-wavelength part of the SiKβ spectrum. Such a significant difference in shape between the X-ray spectra of amorphous silicon and silicyne is attributed to the existence of a pronounced π component in the chemical bonds between silicon atoms in silicyne.

E0 photoreflectance spectra of GaAs: Identification of the features related to impurity transitions

In the room-temperature photoreflectance spectra of moderately doped crystalline GaAs wafers near the fundamental E0 critical point, components corresponding to impurity transitions were identified. This was done by phase analysis of the spectra, and their variation with the laser-excitation density was examined. The dependences of the impurity component magnitude and the retardation phase on the excitation density were determined experimentally. It was established that the impurity component is strongly affected by the condition of the sample surface.

Formation of Silicon Nanocrystals in Multilayer Nanoperiodic a-SiOx/Insulator Structures from the Results of Synchrotron Investigations

The problem of the efficiency of the controllable formation of arrays of silicon nanoparticles is studied on the basis of detailed investigations of the electronic structure of multilayer nanoperiodic a-SiOx/SiO2, a-SiOx/Аl2О3, and a-SiOx/ZrO2 compounds. Using synchrotron radiation and the X-ray absorption near edge structure (XANES) spectroscopy technique, a modification is revealed for the investigated structures under the effect of high-temperature annealing at the highest temperature of 1100°C; this modification is attributed to the formation of silicon nanocrystals in the layers of photoluminescent multilayer structures.

Electronic structure and phase composition of silicon oxide in the metal-containing composite layers of a [(Co40Fe40B20)34(SiO2)66/C]46 multilayer amorphous nanostructure with carbon interlayers

A [(Co40Fe40B20)34(SiO2)66/C]46 multilayer amorphous nanostructure, consisting of alternating metal-containing composite layers and carbon interlayers, has been grown on a rotating glass-ceramic substrate by ion-beam-sputtering two targets, one of which had the form of a metallic plate of the Co40Fe40B20 alloy with quartz inserts. The nonmetallic interlayers were grown by sputtering graphite (second target). In the multilayer nanostructure (MNS), the thickness (~4–8 nm) of the bilayers, consisting of the (Co40Fe40B20)34(SiO2)66 metal- and silicon oxide-containing composite layers and nonmetallic carbon interlayers, was determined by small-angle X-ray diffraction. Experimental data obtained by nondestructive depth profiling of the MNS using ultrasoft X-ray emission spectroscopy of the (Co40Fe40B20)34(SiO2)66 composite layers demonstrate that the composition of the dielectric component of the composite deviates from the stoichiometry of the quartz in the sputter target toward lower oxygen content, leading to the formation of the SiO1.7 suboxide. Fitting Si L2,3 spectra with reference spectra of known phases indicates that the content of the silicon suboxide phase in the composition of the composite layers can reach half of the composition of the dielectric component, with the second half being SiO2. This circumstance can be favorable for increasing the role of a second carrier transport channel (granule–interlayer–granule) and contribute to the previously observed sharp drop in the resistivity and the overall rise in the magnetic permeability of the MNS.

Generalized multilayer model for the quantitative analysis of the electromodulation components of the electroreflectance and photoreflectance spectra of semiconductors in the region of the E0 fundamental transition

With the assumption of the Franz-Keldysh effect as the origination mechanism of the interband electromodulation E0 component, a generalized multilayer model of this effect was proposed. This model includes such physical parameters as the strength of the surface electric field and its decay profile in the space charge region, energy broadening, and partial modulation of the surface electric field. It was shown that the three regions can be defined in the simulated spectra, namely, the low-energy region, the region of main peak, and the high-energy region of the Franz-Keldysh oscillations. The effect of the model parameters on the line shape in these regions was studied. The ranges of the actual parameters were determined from the quantitative analysis of the experimental photoreflectance spectra of GaAs and InP substrates (n=1015 cm−3–1018 cm−3).

Specific features of the atomic structure of metallic layers of multilayered (CoFeZr/SiO2)32 and (CoFeZr/a-Si)40 nanostructures with different interlayers

Multilayered nanostructures (MN) were prepared by ion-beam successive sputtering from two targets, one of which was a metallic Co45Fe45Zr10 alloy plate and another target was a quartz (SiO2) or silicon plate on the surface of a rotating glass-ceramic substrate in an argon atmosphere. The Co and Fe K edges X-ray absorption fine structure of XANES in the (CoFeZr/SiO2)32 sample with oxide interlayers was similar to XANES of metallic Fe foil. This indicated the existence in metallic layers of multilayered CoFeZr nanocrystals with a local environment similar to the atomic environment in solid solutions on the base of bcc Fe structure, which is also confirmed by XRD data. XANES near the Co and Fe K edges absorption in another multilayered nanostructure with silicon interlayers (CoFeZr/a-Si)40 differs from XANES of MN with dielectric SiO2 interlayer, which demonstrates a dominant influence of the Fe–Si and Co–Si bonds in the local environment of 3d Co and Fe metals when they form CoFeSi-type silicide phases in thinner bilayers of this MN.

Atomic and electronic structure of amorphous and nanocrystalline layers of semi-insulating silicon produced by chemical-vapor deposition at low pressures

Semi-insulating silicon SIPOS layers are prepared on single-crystal silicon substrates of two orientations Si (111) and Si (100) by chemical-vapor deposition at a reduced pressure in a horizontal hot-wall reactor at a temperature of 638°C and pressure of P = 20 Pa with a silane flow rate of 8 L/h and the addition of nitrous oxide into the reactor environment. Electronic-structure and phase-composition investigations by ultrasoft X-ray emission spectroscopy (USXES) and X-ray diffraction (XRD) methods show that the addition of nitrous-oxide gas into the reactor environment results in the formation of amorphous silicon layers. The layer-by-layer-phase analysis via USXES of the SIPOS samples to a depth of 120 nm without destruction indicates the predominance of oxide phases in the sample surface layers with a thickness of about 10 nm. The general content of unbound and bound oxygen of less than about 10%, below which nanocrystalline silicon is formed with an average particle size of 60–70 nm, can be considered as some conditional crystallization threshold of SIPOS amorphous layers.