Igor M. Chernev

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

Structure and Optical Properties of Ca Silicide Films and Si/Ca3Si4/Si(111) Heterostructures

Thick, thin films and island of Ca silicide have been grown by Ca deposition onto 500 °C Si (111)7x7 substrates. The crystal structure of the grown layers strongly differs from the known Ca silicides (Ca2Si, CaSi, Ca5Si3, Ca14Si19, CaSi2). The phonon peaks at 389 and 416 cm-1 and the interband transition peaks (0.9-1.0, 1.3-1.7 and 2.0-2.5 eV) belongs to another silicide - Ca3Si4. Peculiarities of crystal, electronic, and phonon structure and optical properties of the grown Ca silicide films were measured by in situ and ex situ methods permit to state that the formed Ca silicide film has a composition Ca3Si4. Heterostructures with embedded Ca3Si4 films with different thicknesses have been formed atop the Ca3Si4 films by MBE and SPE at 500 °C. The observed density of pinholes with different sizes suggests the Si growth atop the Ca silicide follows a 3D mechanism. Photoluminescence was found first time in Si/Ca3Si4/Si (111) heterostructures.

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.

Formation and optical properties of thin Mg2Ge films on Si(001) substrate

Thin Mg2Ge films were grown using two methods: a co-deposition of Ge and Mg on Si substrate kept at room temperature followed by annealing at 200 °C (solid phase epitaxy – SPE) and reactive deposition epitaxy (RDE) of Ge and Mg on Si at 200 °C. Optical properties of these structures were investigated in the photon energy range of 0.02–6.2 eV. Based on optical functions calculation, it was shown that SPE growth results in formation of a crystalline layer of Mg2Si, which exhibits a strong optical phonon originated from the substrate-film interface. In the case of RDE growth, the amount of Mg2Si is sufficiently lower, but Mg‑Si-Ge compound phonon appears. The estimate of a fundamental indirect transition value in the film is 0.72 eV for SPE growth method and 0.56 eV for RDE due to the ternary compound Mg-Ge-Si at the film-substrate interface.

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.

Formation of Bulk and Nanocrystallite Layers of GaSb on Silicon

Formation of GaSb by means of solid phase epitaxy of amorphous Ga:Sb (1:1) layer on Si (001) substrate at 500 °C has been studied. At amorphous layer thickness of 16 nm, a continuous nanocrystalline layer of GaSb was formed. Decreasing of amorphous layer thickness up to 0.8 nm resulted in formation of separated GaSb nanocrystallites (NCs), which had a mean lateral size of 30–80 nm and mean height of 2–3 nm, while their concentration reached 3×109 cm-2. Atomic force microscopy and low energy electron diffraction data showed that GaSb NCs could be fully embedded into silicon lattice by deposition of 25-nm-thick silicon layer at 650 °C. Nevertheless, on a surface of the silicon layer, some holes have been formed because of NCs moving toward to the surface. The holes formation can be almost completely suppressed by deposition of additional 25-nm-thick silicon layer at 500 °C – so-called “stop-layer”.

Non-doped and doped Mg stannide films on Si(111) substrates: Formation, optical, and electrical properties

Thin (45–50 nm) non-doped and doped (by Sb and Al) polycrystalline Mg stannide films consisting mainly of Mg2Sn semiconductor phase and containing small quantity of Mg2Si phase have been grown by multiple layer deposition at room temperature and single step annealing at 150 °C of the (Sn–Mg) bi-layers on Si(111) n-type wafers with 7.5 Ωcm resistivity. Optical spectroscopy data have shown that the grown Mg stannide films is a semiconductor with direct band gap of 0.17 ± 0.03 eV, with second and third direct interband transitions at 0.34 ± 0.02 and 0.45 ± 0.04 eV. An undispersed refraction index: n0 = 3.78 ± 0.06 was calculated from phonon energy dependence of the refraction index of the grown films in the 0.12–0.20 eV energy range. Temperatures dependent Hall effect measurements have revealed about 0.28 eV electrical band gap value in the films.