High-operating-temperature MWIR photodetector based on a InAs/GaSb superlattice grown by MOCVD

We demonstrate a high-operating-temperature (HOT) mid-wavelength InAs/GaSb superlattice heterojunction infrared photodetector grown by metal–organic chemical vapor deposition. High crystalline quality and the near-zero lattice mismatch of a InAs/GaSb superlattice on an InAs substrate were evidenced by high-resolution X-ray diffraction. At a bias voltage of –0.1 V and an operating temperature of 200 K, the device exhibited a 50% cutoff wavelength of ~ 4.9 μm, a dark current density of 0.012 A/cm2, and a peak specific detectivity of 2.3 × 109 cm·Hz1/2 /W.

High Crystalline Quality Conductive Polypyrrole Film Prepared by Interface Chemical Oxidation Polymerization Method

The authors report that polypyrrole (PPy) films with large area and high crystalline quality have been achieved using an interfacial chemical oxidation method. By dissolving different reactants in two immiscible solvents, the PPy is synthetized at the interface region of the two solutions. The PPy films have sharp XRD diffraction peaks, indicating that the molecular chains in the film are arranged in a high degree of order and that they reflect high crystalline quality. High crystal quality is also conducive to improving electrical conductivity. The conductivity of the as prepared PPy film is about 0.3 S/cm, and the carrier mobility is about 5 cm2/(Vs). In addition, the biggest advantage of this method is that the prepared PPy film has a large area and is easy to transfer to other substrates. This will confidently broaden the application of PPy in the future.

Four-inch high quality crack-free AlN layer grown on a high-temperature annealed AlN template by MOCVD

In this work, based on physical vapor deposition and high-temperature annealing (HTA), the 4-inch crack-free high-quality AlN template is initialized. Benefiting from the crystal recrystallization during the HTA process, the FWHMs of X-ray rocking curves for (002) and (102) planes are encouragingly decreased to 62 and 282 arcsec, respectively. On such an AlN template, an ultra-thin AlN with a thickness of ~700 nm grown by MOCVD shows good quality, thus avoiding the epitaxial lateral overgrowth (ELOG) process in which 3–4 μm AlN is essential to obtain the flat surface and high crystalline quality. The 4-inch scaled wafer provides an avenue to match UVC-LED with the fabrication process of traditional GaN-based blue LED, therefore significantly improving yields and decreasing cost.

Control of Competing Thermodynamics and Kinetics in Vapor Phase Thin-Film Growth of Nitrides and Borides

Thin-film growth is a platform technique that allows the preparation of various undeveloped materials and enables the development of novel energy generation devices. Preferred phase formation, control of crystalline orientation and quality, defect concentration, and stoichiometry in thin films are important for obtaining thin films exhibiting desired physical and chemical properties. In particular, the control of crystalline phase formation by utilizing thin-film technology favors the preparation of undeveloped materials. In this study, thin-film growth of transition metal nitride and rare-earth metal boride was performed using remote plasma–assisted molecular beam epitaxy and hybrid physical–chemical vapor deposition techniques, and was successfully achieved by tuning the competition between thermodynamics and kinetics during vapor-phase thin-film growth. Growth conditions of high crystalline quality titanium nitride thin films and high phase purity ytterbium boride thin films were not thermodynamically favorable. Appropriate control of the contribution degree of thermodynamics and kinetics during vapor-phase thin-film growth is crucial for fabricating high phase purity and high crystalline quality thin films.

A Novel Green Synthesis of Zero Valent Iron Nanoparticles (Nzvi) using Walnut Green Skin Characterization, Catalytic Degradation and Toxicity Studies

In the present study, green synthesized nanoparticles were used to activate persulfate and used for oxidation of metronidazole (MTZ). In the process of green synthesis, the walnut green skin was used for the synthesis of zero-valent iron (nZVI) particles. These nanoparticles' FESEM images revealed that they were spherical-shaped nanoparticles with a diameter ranging from 18 to 72 nm. Also, the FTIR spectra indicated the functional groups of polyphenols on the surfaces of the nZVI nanoparticles. Moreover, the XRD pattern illustrated that the synthesized particles possessed a high crystalline quality structure. According to the results, under the optimum conditions, the removal efficiency of the process in degradation of MTZ was 90.3%. LC-MS chromatography showed 7 by-products with reduced toxicity in the reactor outputs. It was found that the green synthesized nZVI had a good effect on the activation of the PS and the PS/nZVI process had a high ability in degradation of MTZ from aqueous solutions.

Synthesis of Vertically Aligned ZnO Nanorods Using Sol-gel Seeding and Colloidal Lithography Patterning

Different ZnO nanostructures can be grown using low-cost chemical bath deposition. Although this technique is cost-efficient and flexible, the final structures are usually randomly oriented and hardly controllable in terms of homogeneity and surface density. In this work, we use colloidal lithography to pattern (100) silicon substrates to fully control the nanorods' morphology and density. Moreover, a sol-gel prepared ZnO seed layer was employed to compensate for the lattice mismatch between the silicon substrate and ZnO nanorods. The results show a successful growth of vertically aligned ZnO nanorods with controllable diameter and density in the designated openings in the patterned resist mask deposited on the seed layer. Our method can be used to fabricate optimized devices where vertically ordered ZnO nanorods of high crystalline quality are crucial for the device performance.

Laser Floating Zone Growth: Overview, Singular Materials, Broad Applications, and Future Perspectives

The Laser Floating Zone (LFZ) technique, also known as Laser-Heated Pedestal Growth (LHPG), has been developed throughout the last several decades as a simple, fast, and crucible-free method for growing high-crystalline-quality materials, particularly when compared to the more conventional Verneuil, Bridgman–Stockbarger, and Czochralski methods. Multiple worldwide efforts have, over the years, enabled the growth of highly oriented polycrystalline and single-crystal high-melting materials. This work attempted to critically review the most representative advancements in LFZ apparatus and experimental parameters that enable the growth of high-quality polycrystalline materials and single crystals, along with the most commonly produced materials and their relevant physical properties. Emphasis will be given to materials for photonics and optics, as well as for electrical applications, particularly superconducting and thermoelectric materials, and to the growth of metastable phases. Concomitantly, an analysis was carried out on how LFZ may contribute to further understanding equilibrium vs. non-equilibrium phase selectivity, as well as its potential to achieve or contribute to future developments in the growth of crystals for emerging applications.

The Study of High Breakdown Voltage Vertical GaN-on-GaN p-i-n Diode with Modified Mesa Structure

In this paper, we fabricated Gallium Nitride (GaN) vertical p-i-n diodes grown on free-standing GaN (FS-GaN) substrates. This homogeneous epitaxy led to thicker GaN epi-layers grown on the FS-GaN substrate, but a high crystalline quality was maintained. The vertical GaN p-i-n diode showed a low specific on-resistance of 0.85 mΩ-cm2 and high breakdown voltage (BV) of 2.98 kV. The high breakdown voltage can be attributed to the thick GaN epi-layer and corresponds to the mesa structure. Improvement of the device characteristics by the mesa structure was investigated using device simulations. We proved that a deeper mesa depth is able to decrease the electric field at the bottom of the mesa structure. Furthermore, a smaller mesa bevel angle will assist the BV up to 2.98 kV at a 60° bevel angle. Our approach demonstrates structural optimization of GaN vertical p-i-n diodes is useful to improve the device performance.