Novel quantum-dot light-emitting diodes based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals are reported. The well-dispersed, single-crystal quantum dots (QDs) exhibit high quantum yields, and tunable light emission wavelength. The demonstration of these novel perovskite QDs opens a new avenue toward designing optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.

Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3)

This Review article summarizes the key advantages of using quantum dots (QDs) as luminophores in light-emitting devices (LEDs) and outlines the operating mechanisms of four types of QD-LED. The key scientific and technological challenges facing QD-LED commercialization are identified, together with on-going strategies to overcome these challenges.

Emergence of colloidal quantum-dot light-emitting technologies

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

Photocatalytic water splitting using semiconductors is attractive for converting solar energy into hydrogen. An efficient and scalable system based on particulate photocatalyst sheets is now shown to exhibit energy conversion efficiency exceeding 1%. Photocatalytic water splitting using particulate semiconductors is a potentially scalable and economically feasible technology for converting solar energy into hydrogen1,2,3. Z-scheme systems based on two-step photoexcitation of a hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) are suited to harvesting of sunlight because semiconductors with either water reduction or oxidation activity can be applied to the water splitting reaction4,5. However, it is challenging to achieve efficient transfer of electrons between HEP and OEP particles6,7. Here, we present photocatalyst sheets based on La- and Rh-codoped SrTiO3 (SrTiO3:La, Rh; ref. 8) and Mo-doped BiVO4 (BiVO4:Mo) powders embedded into a gold (Au) layer. Enhancement of the electron relay by annealing and suppression of undesirable reactions through surface modification allow pure water (pH 6.8) splitting with a solar-to-hydrogen energy conversion efficiency of 1.1% and an apparent quantum yield of over 30% at 419 nm. The photocatalyst sheet design enables efficient and scalable water splitting using particulate semiconductors.

Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%

We report four probe measurements of the low field magnetoresistance in single core/shell GaAs/MnAs nanowires synthesized by molecular beam epitaxy, demonstrating clear signatures of anisotropic magnetoresistance that track the field-dependent magnetization. A comparison with micromagnetic simulations reveals that the principal characteristics of the magnetoresistance data can be unambiguously attributed to the nanowire segments with a zinc blende GaAs core. The direct correlation between magnetoresistance, magnetization and crystal structure provides a powerful means of characterizing individual hybrid ferromagnet/semiconductor nanostructures.

Measurement and simulation of anisotropic magnetoresistance in single GaAs/MnAs core/shell nanowires

Epitaxially oriented silicon nanowires (SiNWs) were grown on (111) Si substrates by the vapor–liquid–solid technique in an atmospheric-pressure chemical vapor deposition (APCVD) system using Au as the catalyst and SiCl4 as the source gas. The dependencies of SiNW growth rate on the growth temperature and SiCl4 partial pressure (PSiCl4) were investigated, and the experimental results were compared with calculated supersaturation curves for Si obtained from a gas phase equilibrium model of the SiCl4–H2 system. The SiNW growth rate was found to be weakly dependent on temperature but strongly dependent on the PSiCl4, exhibiting a maximum value qualitatively similar to that predicted from the equilibrium model. The results indicate that SiNW growth from SiCl4 is limited by gas phase chemistry and transport of reactant species to the growth surface under APCVD conditions. The experimental results are discussed within the context of a gas phase mass transport model that takes into account changes in equilibrium partial pressure due to curvature-related Gibbs–Thomson effects.

Gas phase equilibrium limitations on the vapor–liquid–solid growth of epitaxial silicon nanowires using SiCl4

Formation of ultra-thin quantum dot films by mist deposition

Density functional theory based calculations and experimental analysis on a limited number of real samples are performed to study how the presence of silver intercalated in the van der Waals gap of few-layer MoS2 affects the low-frequency Raman active modes of this material. Silver is found to predominantly affect the breathing-like and shear-like vibrational modes of MoS2. These modes correspond to quasi-rigid movements of each individual layer with a restoring force (and, in turn, frequency) that is determined by modulations in the weak interlayer interactions. Noticeable red-shifts with increasing Ag concentration are found for all low-frequency modes. This finding indicates the potential for low-frequency vibrations as useful gauges for practical determination of silver concentration using low-frequency Raman spectroscopy. This work also describes a semi-classical linear chain model that allows to extrapolate results to a large number of layers. Further, first-principles calculations show how Raman spectroscopy can be used to characterize the quality of the two-dimensional interface between MoS2 and a silver substrate.

https://robots.iopscience.iop.org/article/10.1088/2053-1583/abdbcc/pdf

Low-frequency Raman signature of Ag-intercalated few-layer MoS2

The reaction of Ni films with InP is of technological interest because of the importance of Ni in ohmic contacts to n‐type InP. However, numerous discrepancies are found in the literature concerning the Ni/InP reaction. In this study, bulk and thick film diffusion couples are examined in light of the Ni–In–P phase diagram, and many of the apparent discrepancies in the literature are clarified. Segregation of In and P into Ni–In and Ni–P binary phases is found to be an intermediate stage of the reaction, which is most easily observed in the reaction of thicker Ni layers with InP substrates. However, the Ni2InP ternary phase is found in the final stage of the reaction of Ni films on InP substrates, as predicted by the phase diagram. This sequence of phase formation differs dramatically from that observed in the other Ni/III–V systems that have been examined, and these differences are discussed.

Suzanne E. Mohney

Papers

Measurement and simulation of anisotropic magnetoresistance in single GaAs/MnAs core/shell nanowires

Gas phase equilibrium limitations on the vapor–liquid–solid growth of epitaxial silicon nanowires using SiCl4

Formation of ultra-thin quantum dot films by mist deposition

Low-frequency Raman signature of Ag-intercalated few-layer MoS2

Phase formation in Ni/InP contacts