We have fabricated M_g2Si pn-junction diodes by short-period (30 s and 1 min) annealing between 400 and 480 °C and evaluated the pn-junction depth by EBIC and VC observations. The pn-junction depth of approximately 6 and 30 µm was formed for the annealing conditions of 400 °C, 30 s and 480 °C, 1 min, respectively. By comparing the Ag depth profiles determined by SIMS, we estimated the activation ratio at the pn-junction of approximately 8 and 10% for annealing at 450 and 480 °C, respectively. All diodes showed clear rectifying behavior in J–V characteristic and the spectral photosensitivity below approximately 1.8 µm under zero bias condition.

We fabricated Mg₂Si pn-juncion photodiodes with a shallow mesa structure and a ring electrode using a conventional photolithography process and investigated their electrical and optical character. Dark current densities of about 0.18 and 9 × 10⁻⁴ A/cm² were obtained at room temperature and 100 K under the reverse bias at −3 V. Photoresponse below about 2.1 µm was observed in the shallow mesa-type PDs at room temperature operation. The photosensitivity at 1.31 µm was determined about 22 and 42 mA/W for the bias voltage at 0 and −0.1 V, respectively.

Nitrogen-doped nanocrystalline-FeSi₂ (NC-FeSi₂) thin films were deposited on SiO₂ substrates at room temperature by radio frequency magnetron sputtering, and the effects of nitrogen-doping were experimentally studied. X-ray diffraction measurements revealed that the lattice constant of nano-sized grains increases by nitrogen doping and finally the film becomes amorphous. Optical absorption spectral and electrical measurements indicated that the optical bandgap is evidently enlarged and the electrical conductivity is significantly decreased by nitrogen doping, respectively. It was experimentally demonstrated that nitrogen doping drastically modulate NC-FeSi₂ optically and electrically.

We have evaluated β-FeSi₂ (110), (101) planes epitaxially grown on Si(111) by using ion beam analysis. Unexpected large displacements were deduced from analysis based on single ion scattering. We have discussed multiple ion scattering caused inside the film and obtained the comparatively reasonable atomic displacement of Δx = 0.04 nm that is close to one sixth of one step height of six domains stacking on the (111) planes. This result suggests that multiple scattering may be attributed to the atomic displacement due to the domain stacking faults.

We have investigated oxidation behaviors of nanocrystal (NC) β-FeSi₂/Si composites by Rutherford Backscattering Spectrometry (RBS) and computation of diffusion fluxes. The oxidation is controlled by diffusion of the O flux from the surface and the Si flux toward the Matano–Boltzmann (M–B) interface. The time dependence of the location of the M–B interface was determined. We proposed a model for oxidation of the composite that is different from oxidation of Si controlled by O diffusion through SiO₂ at the surface.

Direct transition energy (E_g) of β-FeSi₂/Si(111) epitaxial films grown at different growth temperatures (T_s) was investigated by photoreflectance (PR) measurements. In Raman spectra, the wavenumber of A_g-mode in Fe–Fe and Si–Si vibrations shifted to higher wavenumber with decrease of T_s. The estimated Si/Fe composition ratio of the epitaxial layer became small (Si-poor) in the films grown at lower T_s. In PR spectra, E_g shifted to higher energy with decrease of T_s. These results show that the modification of electronic structure by a strain induced at β-FeSi₂/Si hetero-interface is suppressed by an increase of Si vacancies in β-FeSi₂.

The reactive deposition epitaxial (RDE) growth method has been employed extensively in the β-FeSi₂ thin film growth. It has been already clarified also that the Fe/Si ratio of source materials affects on the quality of deposited β-FeSi₂ thin films by ion beam sputter deposition under high-vacuum condition. On the other hand, to provide methods capable of depositing a high-quality β-FeSi₂ thin films inexpensively are important as well. In this study, we used a conventional vacuum deposition system and a few different kinds of iron silicides of Fe₂Si, α-FeSi₂, and ε-FeSi, which each contains Si, as the source materials in the RDE growth. We found that the depositing Fe₂Si onto heated Si substrate helps improving the film flatness and the electric properties of the obtained β-FeSi₂ thin films compared to that of Fe-deposited films, even at the relatively low vacuum depositing.

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 × 10¹⁰ cm⁻², 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.

We have realized single phase crystalline BaSi₂ thin films on quartz substrate by vacuum evaporation for solar cell applications. This structure is achieved by introducing (111)-oriented poly-Si fabricated by aluminum induced crystallization as a supply layer prior to BaSi₂ deposition. Raman measurements showed five characteristic peaks corresponding to [Si₄]⁴⁻ anions vibrations in BaSi₂ for all films deposited at 400 °C and above. X-ray diffraction analysis showed that randomly-oriented orthorhombic phase of BaSi₂ is achieved with no trace of secondary phases. Also, the crystal quality is enhanced at higher substrate temperatures.

Thermal evaporation is a simple and high-speed method to grow a BaSi₂ thin film, which is an emerging candidate for an absorber-layer material of thin-film solar cells. In this study, we have investigated the preferred orientation of BaSi₂ films grown at substrate temperatures of 600–700 °C by thermal evaporation using X-ray diffraction. 2θ–ω scans show that peaks derived from (100) orientation grow steadily with increasing substrate temperature. By X-ray pole figure analysis, the (100)-oriented crystals are proven to be epitaxially grown on Si(100) with two variants. The reason of epitaxial growth is discussed from the epitaxial temperature.

Barium disilicide may be considered to be a promising material for solar cells. Thin films of BaSi₂ can be developed in various ways. In this paper, we discuss the properties of a barium silicide film obtained by a solid phase epitaxy. GIXRD method showed the presence of BaSi₂ in the film which was obtained at the temperature T = 600, 750 and T = 800 °C. We hypothesize that the co-precipitation of Ba and Si can solve this problem and find that the increase of the annealing temperature results in better film crystallization (for the selected temperature).

β-FeSi₂ polycrystalline films with p-type conduction were grown by RF magnetron sputtering using a B-doped p⁺-Si target with Fe chips. The hole density and mobility were 2 × 10¹⁷ cm⁻³ and 71 cm² V⁻¹ s⁻¹ at RT, respectively. The acceptor levels formed by the B-doping were obtained to be 10 and 245 meV. In the temperature dependence of electrical properties, the p-type β-FeSi₂ film showed the impurity-band conduction at 77–350 K.

We have investigated oxidation resistance of melt grown Mg₂Si crystals doped with Sb or Bi impurity by thermal annealing above 600 °C, large difference of oxidation speed was observed in the Sb-doped, Bi-doped and non-doped Mg₂Si crystals. The sample weight of Bi-doped and non-doped Mg₂Si increased about 128 and 104%, respectively, while that of Sb-doped one unchanged after thermal annealing at 650 °C for 6 h. TG/DTA analysis also revealed the changing of oxidation speed and reaction temperature in the Sb-doped, Bi-doped, and non-doped Mg₂Si crystals. These results indicate that Sb-dopant improves the oxidation resistance whereas Bi-dopant deteriorates the oxidation resistance of Mg₂Si.

Magnesium silicide (Mg₂Si) is expected as a semiconductor material for thermoelectric devices though synthesis of the thin film has been difficult due to difference in thermodynamic properties of Mg and Si. The authors have succeeded in preparing a poly-crystalline Mg₂Si thin film with a thickness of ~1 µm and strong (111) orientation on a sapphire substrate (r plane). The method includes sputter deposition of a Mg/Si bilayer from independent Mg and Si sources and post-annealing (2 h) in argon gas at 900 Pa. The optimum annealing temperature for the Mg₂Si film synthesis is found to be 300–400 °C.

The magnesium silicide nanoparticles were formed on the surface of hydrogenated silicon thin films by thermal evaporation, annealing and hydrogen plasma treatment. The high reactivity of silicon and magnesium leads to the self-formation of magnesium silicide nanoparticles (NPs). The reaction is stimulated in-situ by the low pressure hydrogen plasma. The presence of Mg₂Si NPs was confirmed by SEM and Raman spectroscopy. The photothermal deflection spectroscopy (PDS) shows the enhanced optical absorption in the near infrared spectrum. The diode structures with in-situ embedded Mg₂Si NPs were characterized by the volt-ampere measurements in dark and under AM1.5 spectrum.

Phase composition of iron silicide nanocrystals (NCs) in the course of formation by solid phase epitaxy (SPE) method, and embedding into silicon was studied. It was found that SPE of 0.4-nm-thick Fe film at 630 °C resulted in formation of small (less than 29.5 nm) and big (more than 42.6 nm) NCs. The former contained only β-FeSi₂ phase and the latter consisted of β-FeSi₂ and ε-FeSi phases. Annealing of these NCs at 750 °C for 90 min led to transformation of β-FeSi₂ and ε-FeSi into α-FeSi₂ NCs. However, when the as-grown NCs have been covered with silicon layer with thickness of 25–380 nm at 750 °C, they turned into β-FeSi₂ NC. Epitaxial relationship and crystal lattice deformation obtained for β-FeSi₂ NCs covered by Si layer is favorable for indirect to direct band gap transition.

Semiconducting β-FeSi₂ is a potential candidate material for solar cells. Various fabrication methods have therefore been proposed for smart films of this material. However, the dynamics of β-FeSi₂ formation are not fully understood and require investigation. Our experimental results based on TEM and SEM observations imply that the mechanism for forming iron silicide is very complex, and exhibits strong dependence on the fabrication method. Rod-like precipitates form in a sample fabricated with double iron deposition and no precipitates form in a sample fabricated with single iron deposition on a silicon substrate.

The morphology and crystalline structure of Si(111)/CaSi₂/Si(111) double heterostructures (DHS) formed by the Ca reactive deposition epitaxy on the Si(111)7 × 7 surface and Si overgrowth at 500 °C have been studied by atomic force microscopy and transmission electron microscopy. It was established that stressed CaSi₂ layers with stacking faults in (001)CaSi₂ plane and {111}-twinned epitaxial or polycrystalline Si layers were grown. Epitaxial Si layers while had orientation parallel to the Si(111) substrate surface. CaSi₂[100]||Si[] and CaSi₂(001)||Si(111) epitaxial relations were conserved for all grown DHS and they did not depend from the silicon growth mode: molecular beam epitaxy (MBE) or solid phase epitaxy (SPE). The CaSi₂ layer in (001)CaSi₂ plane has a hR6 modification and parameters: a = 0.393 ± 0.002 nm; c = 3.09 ± 0.18 nm at SPE Si growth mode. But some another parameters: a = 0.382 ± 0.002 nm; c = 3.09 ± 0.18 nm were observed at MBE Si growth mode. The compression in c parameter on near 1.07–1.14% as compared with c-value (3.06 nm) for tabular CaSi₂ data is established fact for both HDS. The observed differences in a parameter +1.85% (at SPE mode) and −1.08% (at MBE mode) is not clear now, and demands additional experiments. Some assumptions about mechanisms of occurrence and distribution of compressions and stretching in the CaSi₂ lattice were made.

Fe₃Si/FeSi₂/Fe₃Si trilayered junctions were fabricated by facing targets direct-current sputtering combined with a mask method, and the spin valve signals of the junctions were studied in the temperature range from 50 to 300 K. Whereas the magnetoresistance ratio of giant magnetoresistance and tunnel magnetoresistance junctions monotonically increases with decreasing temperature, that of our samples has the maximum value around 80 K and decreases with decreasing temperature at lower than 80 K, which might be due to an increase in the electrical conductivity mismatch between the metallic Fe₃Si layers and semiconducting FeSi₂ interlayer in the low temperature range.

Fe/B-doped carbon/Fe₃Si trilayered films were prepared on Si(111) substrates by physical vapor deposition with a mask method, and the film-structures and magnetic properties of the films were investigated. The Fe₃Si and Fe layers were deposited by facing targets direct-current sputtering (FTDCS), and the B-doped carbon layers were deposited by coaxial arc plasma deposition (CAPD) with B-blended graphite targets. Here, since the B-doped carbon layers were deposited by CAPD in the same manner as the deposition of B-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films, the interlayers should be B-doped UNCD/a-C:H. The formation of a layered structure was confirmed by transmission electron microscopy (TEM). The diffusion of Fe and Si atoms into the interlayer occurs in the range of several nanometers. The shape of the magnetization curve has clear steps that evidently indicate the formation of antiparallel alignment of magnetizations owing to the difference in the coercive forces between the top Fe and bottom Fe₃Si layers. It was experimentally demonstrated that B-doped UNCD/a-C:H is applicable to Fe–Si system spin valves as interlayer materials.