Crystal Research and Technology最新文献

A comprehensive investigation on the uniformity of offcut angles on vicinal GaN substrate surfaces and their impact on both epitaxial growth and electrical characteristics of AlGaN/GaN heteroepitaxial structures is presented. A nearly inverse linear correlation is noted between the substrate's offcut angle and the Al mole fraction in the AlGaN layer. T During AlGaN growth, Ga atoms are obviously incorporated more to smaller atomic terraces as the Al atoms. Localized, non-uniform current conduction channels along the edges of bunched steps were observed. A larger substrate offcut results in higher occurrence of stripes with higher current flow. This affects the Schottky barrier height of diodes that contain different densities of such regions. Ni/Au/AlGaN/GaN Schottky barrier diodes showed a decrease in the average Schottky barrier height on such places. An offcut angle difference from 0.29° to 0.42° yields an approximately 13 meV reduction in average Schottky barrier height. This highlights the significant impact that the transition in surface morphology even at the initial stages could exert on the electrical characteristics of the Schottky barrier diodes. Consequently, it becomes crucial to accurately assess the offcut angle variations over the whole wafer to align epitaxy with the specific performance requirements of the target device.

Partially palladium (Pd) substituted Ni_0.6Cu_0.2Zn_0.2Pd_3xFe_2-2xO₄ (x ≤ 0.1) nano-spinel ferrites (NCZPd_x (x ≤ 0.1) NSFs) have been manufactured via sol–gel combustion route. The phase of all samples has been endorsed by XRD diffraction analysis. Their crystallite size (D_XRD) were estimated within 36–72 nm range. Morphology and the chemical composition have been confirmed by EDX (Energy Dispersive X-ray) and SEM-TEM (Scanning-Transmission Emission Microscopy) respectively. Complex impedance spectroscopy (CIS) was utilized to explore the dielectric characteristics within 20 to 120 ºC temperature and from 1 to 106 Hz frequency ranges. The two-dimentional frequency and temperature dependencies of the real and imaginary components of permittivity (ε^/ and ε^//), the dielectric loss tangent (tan(δ)), the real and imaginary parts of dielectric modulus (M^/ real and M^//), σ ac-conductivity (s), the real and imaginary components of impedance (Z^/ and Z^//), along with the experimental Nyquist diagrams Z^//(Z^/), were constructed and illustrated for all samples. The main feature of the frequencybehavior of the tan(δ) dielectric loss tangent is the presence of pronounced maxima depending on both frequency and temperature. The maximum value of the tan(δ) observed for the significantly doped x = 0.06-0.10 samples. The Pd substitution changes the electron relaxation and microwave absorption resonance.

This study investigates the effect of inserting 50 nm and 100 nm indium nanosheets between tungsten oxide layers to create WO₃/In/WO₃ (WIW) films. Fabricated by vacuum evaporation, these amorphous WIW films showed a 62% reduction in average surface roughness. Indium nanosheets enhanced optical properties, increasing visible and infrared light absorption by 256% at 3.0 eV and 224% at 1.76 eV, while reducing the energy bandgap from 2.94 to 2.11 eV with thicker nanosheets. WIW films exhibited enhanced dielectric and optical conductivity responses leading to an improved terahertz cutoff frequencies values of 1.6–9.6 THz in the light range of 1.13–3.0 eV. Electrical resistivity dropped by two and four orders of magnitude for 50 and 100 nm layers, respectively. These combined improvements make WIW films promising for electro-optical applications.

Silicon carbide (SiC) has important application prospects in power and radio frequency devices. Obtaining SiC crystals with large diameters and high quality is still a challenge. In this work, the temperature field during SiC crystal growth is investigated through the physical vapor transport (PVT) method. Based on the numerical simulated results, an improved growing system is designed and perfect SiC crystals without any edge defects are successfully obtained. Furthermore, the X-ray rocking curve, electrical resistivity, and dislocation density of the obtaining SiC crystals are evaluated.

Nucleation control and separation of ethyl maltol polymorphs Form-II and Form-III from mixed water (W) and ethanol (E) solutions with nine different mixing ratios, ranging from 90W:10E to 10W:90E, is reported for the first time using conventional slow evaporation crystallization method. Solutions with compositions of 90W:10E to 60W:40E induced Form-II, while the remaining five compositions resulted in the nucleation of Form-III. Solubility, refractive index, and pH are determined for these solutions. Form-II nucleated with prismatic-like morphology whereas Form-III exhibited platy-like morphology, as observed through in situ optical microscopy. Structural confirmation, thermal behavior, and possible polymorphic phase transformation are analyzed using powder X-ray diffraction and differential scanning calorimetry.

The authors of a recent paper (Cryst. Res. Technol. 2022, 57, 2100130) report to have grown crystals of triglycine acetate (TGAc) by slow evaporation of an aqueous solution containing glycine and acetic acid in 3:1 molar ratio. The infrared spectrum and unit cell data of the so-called TGAc crystal confirm that it is, in fact, α-glycine. The non-formation of any TGAc is due to no chemical reaction occurring between glycine and acetic acid. Another publication (Cryst. Res. Technol. 2022, 57, 2100262) describes the growth and characterization of a so-called triglycine oxalate (TGO) crystal. The unit cell data and infrared spectrum of the TGO crystal reveal that the crystal grown is, in fact, the well-known glycinium hydrogen oxalate. A critical analysis of the publications reporting on the growth of triglycine phosphate (TGP) and triglycine formate (TGF) crystals reveals that these are not what the authors claim them to be. Despite their names, the TGAc or TGP or TGO or TGF crystals are not analogs of the triglycine sulfate (TGS) crystal but serve as examples to highlight the importance of single-crystal structure refinement to avoid improper characterization.

The unique morphology and structure significantly enhance the performance of photoelectric detection. Herein, titanyl phthalocyanine (TiOPc) coarse crystal and microspheres are obtained by a simple physical vapor deposition (PVD) method designed to produce TiOPc structures that undergo significant changes in the crystal structure. The photoelectric experimental results show that the photocurrent of TiOPc coarse crystal and microspheres increases with the increase of voltage and exhibits better stability compared to the raw materials. Under a bias voltage of 10 V, the photoresponsivity of microspheres reaches the maximum, which is 77 times that of raw materials. Under different monochromatic lights, the raw materials are most sensitive to red light (850 nm), with a photocurrent of 1.3556 × 10⁻⁶ mA, but the coarse crystal/microspheres are most sensitive to blue light (455 nm) with photocurrents of 1.281 × 10⁻⁵ mA/2.609 × 10⁻⁵ mA, respectively. It is worth mentioning that although the photocurrent and responsivity of coarse crystal are slightly lower than those of microspheres, the response speed is faster, with a rise/fall time is 271 and 194 ms, respectively. The good photoelectric properties indicate the potential research value of TiOPc coarse crystal and microspheres in the field of photoelectric detection.

β-Ga₂O₃ is a promising wide band gap material for power device and solar-blind photodector applications. With continuous contribution to the crystal growth of β-Ga₂O₃, it is important to conclude the progress of crystal growth techniques and the remaining problems of the materials propel the next generation of the power device industry. The size of single crystals becomes larger, the quality of epitaxial films is gradually improved, and the performance of devices has become better. β-Ga₂O₃ is an oxide semiconductor with a large bandgap width of 4.7–4.9 eV and a high breakdown electric field of ≈8 MV cm⁻¹. In this review, the structure, thermal properties, optical properties, and electronic properties of β-Ga₂O₃ are introduced first. Then, the growth methods of bulk β-Ga₂O₃ single crystals are introduced, including the Verneuil method, Czochralski (CZ) method, optical-floating zone (OFZ) method, edge-defined film-fed growth (EFG) method, vertical Bridgman (VB) method, casting method, and the oxide crystal growth from cold crucible (OCCC) method. Crystal growth mechanisms and their respective advantages and disadvantages are discussed. The effects of doping elements on the crystal growth have been highlighted in each method. Finally, the prospect of the growth of large β-Ga₂O₃ single crystals is discussed.

The flexibility and adaptability of low-dimensional halide perovskites make them ideal candidates for a wide range of cutting-edge technologies. In addition to their primary applications in photovoltaics, they have recently attracted attention for their potential use in switchable technologies such as smart windows, encrypted messages, and sensors. The interest stems from their switchable properties, which enable them to change their physical properties, in particular photoluminescence and crystal color, in response to external stimuli such as heat, light, pressure, and humidity. This review examines their switchable properties and explores their practical applications in a number of emerging chromic technologies. This paper also provides an in-depth analysis of the reversibility, switchable optical and electrical properties of low-dimensional halide perovskites, and the switching mechanisms involved in the transformations they undergo. In addition, the paper is classified according to different switching mechanisms. To assist the research community in developing new designs for new switchable low-dimensional perovskites, some basic criteria for effective switching materials are outlined here. Finally, the current challenges facing these emerging materials are discussed, and an outlook on future developments and potential breakthroughs in this promising area of research is provided.