Konstantin N. Galkin

OPTICAL AND ELECTRONIC PROPERTIES OF M2Si (M = Mg, Ca, Sr) GROWN BY REACTIVE DEPOSITION TECHNIQUE

Single phase M2Si (M = Mg, Ca, Sr) silicides were grown using Si substrates, by thermal treatment of the substrates in the vapors of the metallic sources, M, and the electronic structures and optical property of the silicides were investigated. The electronic band structures of the silicides were calculated using the first-principles total-energy calculation program in pseudopotential schemes with plane-wave basis functions. The calculated optical reflectance spectra were also deduced from the theoretical band structures, and roughly agreed with the experimental results except for the low reflectance intensity around 2 eV. This suggests that the energy band gap of the silicides roughly agree with the calculated values of 0.15, 0.31 and 0.35 eV for Mg2Si, Ca2Si and Sr2Si, respectively, within the underestimation of the band gap by the density functional calculation. The optical property of the silicides is also discussed in relation to the morphological structures of the silicides.

Study of ultrathin iron silicide films grown by solid phase epitaxy on the Si(001) surface

Ultrathin films of iron silicide have been grown by high-temperature annealing of 0.14-to O.5O-nm-thick Fe films deposited on the Si(001) surface at room temperature. It has been found that annealing leads to the formation of nanoislands of iron silicide on the surface, so that their type depends on the thickness of the Fe film. High-energy electron diffraction and atomic force microscopy measurements have revealed that the deposition of Fe films less than 0.32 nm thick on the Si(001) surface stimulates epitaxial growth of both three-dimensional β-FeSi2 and two-dimensional γ-FeSi2 islands. It has been found that, for Fe coverages of more than 0.32 nm thick, a complete transition to solide phase epitaxy is observed only for two-dimensional β-FeSi2 islands. The effect of prolonged annealing at 850°C on the morphology of the surface of the iron silicide film has been investigated.

Influence of Cr+ ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi2/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 1015 to 6 × 1016 cm−2 and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi2) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 1016 cm−2. At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi2 precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.

Pulsed modification of germanium films on silicon, sapphire, and quartz substrates: Structure and optical properties

The structural and optical properties of thin Ge films deposited onto semiconducting and insulating substrates and modified by pulsed laser radiation are studied. The films are deposited by the sputtering of a Ge target with a low-energy Xe+ ion beam. Crystallization of the films is conducted by their exposure to nanosecond ruby laser radiation pulses (λ = 0.694 μm) with the energy density W = 0.2−1.4 J cm−2. During pulsed laser treatment, the irradiated area is probed with quasi-cw (quasi-continuous-wave) laser radiation (λ = 0.532 and 1.064 μm), with the reflectance recorded R(t). Experimental data on the lifetime of the Ge melt are compared with the results of calculation, and good agreement between them is demonstrated. Through the use of a number of techniques, the dependences of the composition of the films, their crystal structure, the level of strains, and the reflectance and transmittance on the conditions of deposition and annealing are established.

Formation and properties of p-i-n diodes based on hydrogenated amorphous silicon with embedded CrSi2, Mg2Si and Ca2Si nanocrystallites for energy conversion applications

1Institute of Automation and Control Processes of Far Eastern Branch of RAS, Vladivostok, 690041, Radio, 5, Russia 2Institute of Chemical Process Fundamentals of the ASCR, v. v. i., Rozvojova 135, 165 02 Praha 6, Czech Republic 3 Institute of Physics of the ASCR, v. v. i., Cukrovarnicka 10/112, 162 00 Praha 6, Czech Republic 4Czech Technical University in Prague, Faculty of Biomedical Engineering, Sitna 3105, 27201 Kladno, Czech Republic

Solid phase epitaxy formation of silicon-GaSb based heterostructures

A double-layer heterostructure with embedded into single-crystalline silicon matrix nanocrystallites of gallium antimonide was grown. GaSb was formed by solid phase epitaxy method using Ga-Sb stoichiometric mixture of 2-nm-thick and a stepped annealing from 200 to 500 °C. The obtained nanocrystallites have a concentration of 7.1×10 cm, a height of 4.6 nm and lateral dimensions of 16–20 nm. The GaSb nanocrystallites were covered with silicon layer using molecular beam epitaxy in two stage: 40-nm-thick at 300 °C followed by 60-nm-thick at 500 °C.

The structure and magnetic properties of bronze, stainless still and alloy layers formed by direct laser welding on nonmagnetic substrates

Investigations of crystal structure, microstructure and composition of laser welded coatings of bronze, IN625, PGSR-4 and stainless steel alloys on non-magnetic substrates have shown that from the raw alloy powders (wire) the additional crystalline phases are extracted with new compositions and sizes of units of microns, which randomly distributed in the coating volume. Due to formation of additional phases with increased electron concentration magnetic hysteresis loops have appeared at 4 K and 300 K for all welded coatings. Bronze and stainless steel coatings have demonstrated soft ferromagnetic properties with two type of magnetic domains with small magnetization that resulted in small value of saturation magnetization (Ms = 60-146 emu/cm3 at 300 K and Ms = 107-241 emu/cm3 at 4 K) and low values of coercive force (40 – 90 Oe) at 300 K and (50-170 Oe) at 4 K. En existence of one type of ferromagnetic domains with middle Curie temperatures (230-270 K) in laser welded IN625 and PGSR-4 coatings has determined soft ferromagnetic nature of magnetism at low temperature (Ms =274 – 398 emu/cm3) and transition in paramagnetic conditions at 300 K due to main contribution only paramagnetic grains with different composition.

Extended near-IR Spectral Sensitivity and Electroluminescence Properties of Silicon Diode Structure with GaSb/Si Composite Layer

An array of GaSb nanocrystallites (NCs) was formed on Si(001) substrate by solid-phase epitaxy at 500 °C. Owing to the embedded GaSb NCs, p+‑Si/NC‑GaSb/n‑Si mesa diode spectral sensitivity has extended up to 1.6 µm at room temperature, and its integral sensitivity has increased by 4–5% in the wavelength range of 1200–1600 nm, as compared to a conventional Si diode. This result was achieved by embedding only 10 nm of GaSb in the form of NCs inside a silicon matrix. In addition, we could obtain a significant electroluminescence (EL) signal at 120 K in a very wide wavelength range from 1.3 to 2.1 µm (0.95–0.59 eV). The EL spectrum has a broad maximum at 1700 nm (0.73 eV). The threshold pumping current density was as low as 0.75 A/cm2.

Mg2SixSn1-xheterostructures on Si(111) substrate for optoelectronics and thermoelectronics

Thin (50-90 m) non-doped and doped (by Al atoms) Mg2Sn0.6Si0.4 and Mg2Sn0.4Si0.6films with roughness of 1.9-3.7 nm have been grown by multiple deposition and single annealing at 150 °C of multilayers formed by repetition deposition of three-layers (Si-Sn-Mg) on Si(111) p-type wafers with 45 Ω-cm resistivity. Transmission electron microscopy has shown that the first forming layer is an epitaxial layer of hex-Mg2Sn(300) on Si(111) substrate with thickness not more than 5-7 nm. Epitaxial relationships:hex-Mg2Sn(300)|| Si(111), hex-Mg2Sn[001]|| Si[-112] and hex-Mg2Sn[030]||Si[110] have been found for the epitaxial layer. But inclusions of cub-Mg2Si were also observed inside hex-Mg2Sn layer. It was found that the remaining part of the film thickness is in amorphous state and has a layered distribution of major elements: Mg, Sn and Mg without exact chemical composition. It was established by optical spectroscopy data that both type films are semiconductor with undispersed region lower 0.18 eV with no= 3.59 ± 0.01, but only two direct interband transitions with energies 0.75-0.76 eV and 1.2 eV have been determined. The last interband transition has been confirmed by photoreflectance data at room temperature. Fourier transmittance spectroscopy and Raman spectroscopy data have established the formation of stannide, silicide and ternary compositions.

Fibrous Noble Opals: Electron and Atomic-Force Microscopy and Spectrometry Data

The work deals with results of study of hydrothermal noble opals. It has been established that hydrothermal opals are composed of multiple clusters: chaotic packs, fibers and grid layers. An effect of the water saturation coefficient on the opal optical properties was considered.