Фазовый состав и структура пленки BiFeO-=SUB=-3-=/SUB=-, выращенной на подложке MgO(001) методом ВЧ-катодного распыления в атмосфере O-=SUB=-2-=/SUB=-

The crystal structure and Mossbauer spectroscopy studies results for BiFeO3 film growth on the MgO(001) single crystal substrate are present in the paper. It been shown that film have high crystal perfection and low defectiveness which results in appearing of narrow lines during the θ-2θ and φ scanning and the small (lower than 0.7°) disorientation of film and substrate crystal axes. It is been revealed that unit cell of BiFeO3/MgO(001) heterostructure possess monoclinic symmetry and deformation of unit cell is negligible. The Mossbauer study shows that magnetic subsystem of film has spatial spin-modulated structure with zero value of anharmonicity parameter (m). This indicate that at room temperature the magnetic anisotropy changes from the "easy axis" type to "easy plane" type.

EFFECT OF PASSIVATING COATINGS ON METALLIZATION TOPOLOGY IN PRODUCTION OF SEMICONDUCTOR DEVICES

The surface quality of the metallized contact pads on the crystal plays an important role in the production of semiconductor devices. This paper presents experimental studies of the effect of a protective passivation film of silicon oxide on the surface structure of aluminum metallization in the field of forming contact pads. Plasma chemical deposition of passivation layer SiO2 from gas phase (PECVD method) was carried out on prepared samples of silicon with aluminum metallization using a high-frequency power source with a frequency of 13.56 MHz. After that, chemical etching of precipitated silicon oxide was carried out to simulate the process of forming contact areas of semiconductor device crystals. The resistance of the metallization surface to plasma processes was studied by raster electron microscopy. It is shown that as a result of the process cycle, defects of the dislocation type are generated in the applied film Al. The nature of the observed defects has been found to be different. The revealed large square-shaped pits with a size of ~ 1 μm at the places where dislocations come to the surface are of a single nature and appear independently of the processes of applying passivation coatings, which is determined by the orienting action of a single-crystal substrate having some low dislocation density. While the second type of defects, shown by the presence of etching pits measuring ~ 100-300 nm, is characterized by a higher surface density. Moreover, the exclusion of the passivation process with silicon oxide did not lead to the appearance of this type of defects, which determined their nature associated with the ion bombardment of the Al layer during the plasma chemical deposition of silicon oxide from the gas phase. It is also shown that a feature of this type of defects is their disorientation both with respect to the first type of defects and with respect to each other. Detection of the structure of the metallization layers was carried out by X-ray diffraction, the results of which show the polycrystallinity of the formed aluminum metallization. The preferred orientation of the aluminum film corresponds to the substrate Si (111).

Study on the Mechanism of Solid-Phase Oxidant Action in Tribochemical Mechanical Polishing of SiC Single Crystal Substrate

Na2CO3—1.5 H2O2, KClO3, KMnO4, KIO3, and NaOH were selected for dry polishing tests with a 6H-SiC single crystal substrate on a polyurethane polishing pad. The research results showed that all the solid-phase oxidants, except NaOH, could decompose to produce oxygen under the frictional action. After polishing with the five solid-phase oxidants, oxygen was found on the surface of SiC, indicating that all five solid-phase oxidants can have complex tribochemical reactions with SiC. Their reaction products are mainly SiO2 and (SiO2)x. Under the action of friction, due to the high flash point temperature of the polishing interface, the oxygen generated by the decomposition of the solid-phase oxidant could oxidize the surface of SiC and generate a SiO2 oxide layer on the surface of SiC. On the other hand, SiC reacted with H2O and generated a SiO2 oxide layer on the surface of SiC. After polishing with NaOH, the SiO2 oxide layer and soluble Na2SiO3 could be generated on the SiC surface; therefore, the surface material removal rate (MRR) was the highest, and the surface roughness was the largest, after polishing. The lowest MRR was achieved after the dry polishing of SiC with KClO3.

Giant Wrinkles on the Surface of Epitaxial BaTiO3 Thin Films with Drastic Shrinkage during Transfer from a MgO(100) Single-Crystal Substrate to a Flexible Polyethylene Terephthalate Sheet

The transfer of ferroelectric and piezoelectric BaTiO3 epitaxial thin films from an original MgO(100) single-crystal substrate to a polyethylene terephthalate (PET) sheet has been studied to fabricate flexible epitaxial functional oxides. The outline of our previous transfer process is as follows: the epitaxial BaTiO3 thin films were deposited on the MgO(100). Then, the surface of the BaTiO3 was adhered onto a PET sheet. Finally, only the MgO(100) substrate was dissolved in a phosphoric aqueous solution, which resulted in the transfer of the epitaxial BaTiO3 thin film from the MgO(100) to a PET sheet. To establish this transfer process, our aim was to prevent any damage, such as cracks and exfoliation, during the transfer of the epitaxial functional oxides. We found that a Pt buffer layer with a ductile nature was effective for improving the quality of transferred epitaxial BaTiO3 thin films. Moreover, the epitaxial BaTiO3 thin films showed a drastic shrinkage of ca. 10%. The surfaces of the shrunk, epitaxial BaTiO3 thin films showed giant wrinkles with a micrometer-order amplitude and a 10-μm-order periodicity without any damage. The epitaxial BaTiO3 thin films with giant wrinkles, accompanied by drastic shrinkage, are similar to the thin films that are coated on a pre-stretched elastomer, which is one of the fabrication processes of stretchable devices.

Optical Properties of Monocrystalline Silicon Nanowires

The paper presents the results of a study of the optical reflection and transmission spectra of a silicon single crystal p-Si (100) with silicon nanowires grown on both sides and porous silicon p-Si (100) on a single crystal substrate in the spectral range 0.2 ÷ 1.7 μm. The layers of nanowires had a thickness of 5.5 µm, 20 µm, 50 µm and a porosity of 60 %. The porous silicon layers had a thickness of 5 μm, 50 μm and a porosity of 45 %, 55 % and 65 %. The change in the energy band structure in single-crystal silicon nanowires and in a single-crystal matrix of porous silicon is shown.

The Influence of the Preheating Temperature of the (−2 0 1) β-Ga2O3 Substrates on c-Plane GaN Epitaxial Growth

In this paper, we demonstrate the direct epitaxial growth of c-plane GaN on a preheated (−2 0 1) β-Ga2O3 single-crystal substrate with no interlayer or pre-patterning processes by using the atmospheric pressure metalorganic chemical vapor deposition method. The results show that high-temperature preheating (>500 °C) can modify the surface morphology of the substrate so that the crystalline quality of the grown GaN layer can be improved. With higher preheated temperatures, the grown GaN layer reveals smaller FWHM (full width at half-​maximum) of the X-ray rocking curve. In addition, we find that the photoluminescence spectra of the GaN layers reveal their narrowest linewidth at a preheated temperature of 800 °C. These results support improvements of crystalline quality and provide optimization of a c-GaN grown epitaxially on the preheated (−2 0 1) β-Ga2O3 substrates for further device fabrication.

Photo-Diodes Based on CH3NH3PbCl3 Perovskite Single Crystals by Epitaxial Growth for Ultraviolet Photo-Detection

Organic-inorganic hybrid methylammonium lead halide perovskite MAPbX3 (where MA = CH3NH3, and X = Cl, Br, I) single crystals are potential semiconductors for photo-detection due to their excellent optoelectronic performance. In particular, MAPbCl3 single crystal is a wide-band-gap (2.9 eV) semiconductor which is suitable for ultraviolet (UV) detection. In this work, n−-n+ photo-diodes are fabricated through solution-processed epitaxial growth, growing Bi-doped MAPbCl3 epitaxial layer on MAPbCl3 single crystal substrate. The epitaxial layer effectively improves the interface between n−-type and n+-type layers and leads to low dark current. This work provides useful information for UV detection based on perovskites.

Inhomogenous Amorphous Content and Enhanced Piezoelectric Properties in Bi12TiO20-based Composite Ceramics

Bi12TiO20-based composite ceramics were prepared by sintering a mixture of presynthesized Bi12TiO20 and a second phase around the melting point of Bi12TiO20. These ceramics can exhibit direct as well as inverse piezoelectricity without electrical polarization, and become competitive piezoelectric material with high depoling temperature and stable thermal behavior. However, their piezoelectric constants were, in general, relatively low and do not remain consistent for both the symbol and magnitude over the entire surface. To prevent the permeation of melting Bi12TiO20 into substrate and thus create the inhomogenous amorphous content, samples were sintered on Al2O3 (0001) single crystal substrate. Compared to samples sintered on Al2O3 ceramics, piezoelectric coefficient (d33) of these samples was increased by 80%. Moreover, the symbol of d33 is identical on the whole surface. Here, the enhanced piezoelectricity might be ascribed to increased alignment of distorted BiO5 polyhedra in amorphous Bi12TiO20 phase. These results provided a method to improve the piezoelectric properties of Bi12TiO20-based ceramics and provided some inspiration for further development of Bi12TiO20-based ceramics suitable for practical applications.