Magnesium silicide (Mg₂Si) is a promising material for SWIR photodetectors due to its suitable band gap and compatibility with low-cost processing. In this study, dislocations in Mg₂Si single crystals were investigated using the etching observation method. Cleaved {111} surfaces were etched with a dilute HF/HNO₃ solution. The resulting surface structures were analyzed using differential interference contrast microscopy, laser microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The etching revealed the appearance of pits and hillocks aligned along small tilt grain boundaries (STGBs).

MoO₃/graphite composite structures were synthesized by heat treatment of Mo wires and graphite powder in air, and their morphological and structural properties were investigated. MoO₃ nanosheets were epitaxially formed on graphite nanosheets with crystallographic relationships of [100]_MoO3 // [0001]_graphite and [010]_MoO3 // [2110]_graphite. The temperature and duration of the heat treatment affected the formation of the MoO₃/graphite composite structure. This method enables the synthesis of MoO₃/graphite composites with well-defined crystallographic orientation relationships, thereby facilitating enhanced properties for a wide range of applications.

A pn-junction photodiode (PD) was fabricated on a Mg₂Si substrate using an ion implantation process. The PD, featuring an 80 µm square light detection area, was formed by implanting Ag ions as p-type impurities into the n-type Mg₂Si substrate, followed by annealing, using a conventional photolithography process. Annealing at 480 °C effectively recovered crystallinity, activated the Ag dopant, and resulted in good rectification I-V characteristics. Furthermore, the device exhibited distinct photoresponsivity in the SWIR region, with sensitivity extending up to approximately 2.1 µm. These results demonstrate that the Ag ion implantation method is a promising technology for manufacturing SWIR photodetectors, capable of precisely controlling miniaturized device structures.

Local and non-local vertical trilayer spin valve films comprising ferromagnetic Fe₃Si layers and semiconducting nanocrystalline FeSi₂ interlayers were prepared by sputtering combined with a mask method, and spin valve signals were measured at room temperature. The local spin valve signals were observed at different FeSi₂ interlayer thicknesses of 5, 10, 50, and 100 nm. Spin-polarized currents were generated from ferromagnetic Fe₃Si layers into semiconducting nanocrystalline FeSi₂ layers at room temperature. They might be because carriers in the FeSi₂ layers are transported in hopping conduction. On the other hand, the non-local spin valve signals were also observed at the FeSi₂ film thickness of 10 nm. Spin accumulation, so-called pure spin current, was generated from ferromagnetic Fe₃Si layers into semiconducting FeSi₂ layers at room temperature. Nanocrystalline FeSi₂ that can be deposited technically easily is a new spin transport semiconductor and hopping conduction does not drastically lessen the spin transport length.

Strontium-based silicides and related compounds were synthesized by annealing mixtures of CaSi₂, MgCl₂, and Sr powders under an Ar atmosphere. Flake-shaped SrCaSi sheets were formed at 800 °C, whereas stacked nanosheet-like α-SrSi₂ structures were obtained at 1000 °C. The reaction was strongly dependent on the temperature and source ratios, yielding layered silicides together with carbonate byproducts. When mixed sources were used, SrCO₃ was mainly formed, whereas in the Sr–Si system, SrSi₂ appeared as the dominant phase despite the presence of other secondary products. These results demonstrate that careful control of the starting composition and annealing conditions enables the selective growth of layered Sr–Si compounds.

Chromium-based nanostructures were synthesized from CaSi₂ and CrCl₂·6H₂O powders through controlled thermal annealing under various atmospheres. The selective formation of CrSi₂ and Cr₂O₃ was achieved by tuning the reaction temperature and ambient conditions. CrSi₂ appeared as nanorods densely covering the surfaces of gently curved, stacked nanosheets, with rods typically ~100 nm in diameter at the base and elongated along the [0001] axis. The nanosheets were primarily composed of silicon layers, which acted as scaffolds for nanorod growth. In contrast, Cr₂O₃ formed an entangled wire network with variable diameters, creating a porous morphology that was distinct from the ordered CrSi₂ structures.

BaSi₂ is expected as a highly efficient thin film solar cell material. In this study, BaSi₂ film deposition was carried out on n-type Si substrates by vacuum evaporation and properties of BaSi₂ films were investigated. In BaSi₂ deposition, a low-substrate-temperature layer deposited at 400 ℃ or 450 ℃ was introduced at the initial stage of deposition to reduce cracks in the obtained films. As a result of introducing a low-temperature BaSi₂ layer, BaSi₂ films with the thickness of more than 1 µm and with reduced cracks were obtained.

We report the formation of nanocrystalline Mg₂Si thin films deposited using co-deposition via high-power impulse magnetron sputtering (HiPIMS) with a segmented Mg-Si target. The peak power density was estimated to be 0.26 kWcm^-2. The films were deposited on heated silicon substrates at a substrate temperature set to 400 °C without a substrate bias. X-ray diffraction and X-ray photoelectron spectroscopy indicated the formation of the Mg₂Si crystalline phase on the as-deposited surface without post-annealing. Scanning electron microscopy revealed a crack-free surface with nanoscale crystallites of 30–150 nm, exhibiting clear facets.

Indium antimonide (InSb) is a promising material for infrared photodetectors owing to its narrow bandgap and high carrier mobility. In this study, InSb thin films were deposited on Si substrates by radio-frequency sputtering and their structural and electrical properties were investigated. The film thickness was controllable by adjusting deposition time, and annealing promoted crystallization of the films. Based on optimized conditions, n-InSb/p-Si pn-junction photodiodes were fabricated, exhibiting clear rectifying I–V characteristics and distinct photoresponse under illumination with infrared LEDs of 1310 and 1550 nm. These results demonstrate the potential of sputtering as a low-cost and scalable method for InSb-based infrared detectors.

To investigate the cause of the low open circuit voltage V_OC in Mg₂Si-TPV cells, the temperature dependence of output characteristics was examined. The experimental results revealed a V_OC of 0.358 V at 100 K under irradiation from a 1310 nm single-wavelength LD, revealing the significant impact of the saturation current I_s on V_OC, The results indicate that reducing the I_s is important to obtain a favorable V_OC. TCAD simulations estimated that leakage current via recombination centers adversely affects the output characteristics of the TPV cell.