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%

Isothermal sections of the In–Ni–P phase diagram have been determined at 600 °C and 470 °C. Two new ternary phases not previously identified in bulk samples were found. A phase with the composition Ni57In22P21 is present at both 600 °C and 470 °C and was found by differential thermal analysis to melt at 736 °C. The phase Ni2InP was found to be in equilibrium with InP at 470 °C, but it does not appear in the 600 °C isotherm since it melts at 526 °C. The phases (In), Ni2P, Ni5P4, and NiP2 are in equilibrium with InP at both temperatures studied.

Phase equilibria and ternary phase formation in the In–Ni–P system

We report four probe measurements of the low field magnetoresistance (MR) in single core/shell GaAs/MnAs nanowires (NWs) 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

Geometrical and surface effects can significantly alter conduction through metal/semiconductor nanowire (NW) contacts. In this study, we use three dimensional device simulations to examine these effects in detail. Based on the results of these simulations, a methodology is proposed for the extraction of Schottky barrier heights of contacts to semiconductor nanowires. The Schottky barrier height extracted from the current–voltage (I–V) characteristics can differ from the true barrier height due to tunneling contributions localized at the metal/nanowire interface along the nanowire periphery. The outlined method is used to analyze experimental I–V characteristics of a surround-gate axially-aligned θ - Ni 2 Si / n - Si nanowire Schottky barrier contact.

Extracting the Schottky barrier height from axial contacts to semiconductor nanowires

We have used deep-level transient spectroscopy (DLTS) to investigate the electron trap defects introduced in n-GaN during the fabrication of Pt Schottky contacts by electro-deposition, electron beam deposition and sputter deposition under three different deposition conditions. The results indicate that electro-deposition is the only one of these processes that does not introduce any defects. Diodes fabricated by this technique also have the best rectification properties. Both electron beam deposition and sputter deposition introduce electron traps in concentrations that increase towards the Pt/GaN interface. However, sputter deposition at a lower power and higher pressure results in significantly reduced defect concentrations and improved rectification properties.

Processing-induced electron traps in n-type GaN

Antimonide-based compound semiconductors are promising candidates for high-frequency, low-power electronic devices as well as a variety of optoelectronic devices. To assist with the design of shallow or thermally stable contacts, we have performed thermodynamic calculations to estimate ternary phase equilibria in many of the transition metal-Ga-Sb systems. We have used the results of our calculations and a limited number of experiments to identify candidates for nonreactive elemental contacts to GaSb. Both W and Re are clearly in thermodynamic equilibrium with GaSb under the conditions considered in our study. Metal gallides and antimonides that are candidates for thermally stable contacts to GaSb are also highlighted.

Suzanne E. Mohney

Papers

Phase equilibria and ternary phase formation in the In–Ni–P system

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

Extracting the Schottky barrier height from axial contacts to semiconductor nanowires

Processing-induced electron traps in n-type GaN

Condensed phase equilibria in transition metal-Ga-Sb systems and predictions for thermally stable contacts to GaSb