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%

A method is proposed to account for the effects of Schottky barrier height inhomogeneities on the Richardson constant (A∗) extracted from current-voltage-temperature (I-V-T) measurements. Our approach exploits a correlation between the extracted Richardson constant and effective barrier height. As a test case, the method is applied to I-V-T measurements performed on IrOx/n-ZnO Schottky diodes. A homogeneous A∗ value of 27±7 A cm−2 K−2 is obtained, in close agreement with the theoretically expected value of 32 A cm−2 K−2 for n-type ZnO.

Extracting the Richardson constant: IrOx/n-ZnO Schottky diodes

The oxidation of unintentionally doped p-type silicon nanowires grown by the vapor-liquid-solid (VLS) method and their integration into top-gated field effect transistors is reported. Dry thermal oxidation of as-grown silicon nanowires with diameters ranging from 20to400nm was carried out at 700 and 900°C with or without the addition of a chlorinated gas source. The oxidation rate was strongly dependent on the as-grown nanowire diameter, with the large-diameter nanowires oxidizing up to five times faster than the smallest nanowires at 900°C. At each diameter, the addition of trichloroethane (TCA) enhanced the rate compared to oxidation in pure O2. Top-gated field effect transistors fabricated from nanowires oxidized at 700°C had significantly less hysteresis in their subthreshold properties when TCA was added, but oxidation at 900°C with or without TCA provided hysteresis-free devices with improved subthreshold slope. Such enhancements in the electrical properties are expected based on advances in planar ...

Oxidation of silicon nanowires for top-gated field effect transistors

The annealing conditions and contact resistivities of Ta/Al ohmic contacts to n-type GaN are reported for the first time. The high temperature stability and mechanical integrity of Ti/Al and Ta/Al contacts have been investigated. Ta/Al (35 nm/115 nm) contacts to n-type GaN became ohmic after annealing for 3 min at 500°C or for 15 s at 600°C. A minimum contact resistivity of 5×10−6Ω cm2 was measured after contacts were repatterned with an Al layer to reduce the effect of a high metal sheet resistance. Ti/Al and Ta/Al contacts encapsulated under vacuum in quartz tubes showed a significant increase in contact resistivity after aging for five days at 600°C. Cross section transmission electron microscopy micrographs and electrical measurements of aged samples indicate that the increased contact resistivity is primarily the result of degradation of the metal layers. Minimal reactions at the metal/GaN interface of aged samples were observed.

Study of contact resistivity, mechanical integrity, and thermal stability of Ti/Al and Ta/Al ohmic contacts to n-type GaN

Nickel germanide contacts are expected to play an important role in Ge-based electronics similar to that of their nickel silicide counterparts in Si devices. Here we have studied the solid state reaction between Ni contact pads and Ge nanowires. We observe the formation of axial nickel germanide segments after annealing at temperatures as low as 300 °C for 2 min. The nickel germanide segments are polycrystalline, without an epitaxial relationship to the Ge nanowire, in contrast to observations of epitaxial nickel silicide formation from Si nanowires. The crystal structure of the nickel germanide phase is consistent with the Ni2In prototype structure. Annealing above 400 °C results in fracture in the nickel germanide segment; however, nickel germanide segments as long as 1.7 μm can be formed by annealing at 400 °C for 5 min.

Formation of nickel germanide contacts to Ge nanowires

Multilayer ohmic contacts with differing first metal layers (M = Mo, Pd, Pt) beneath a Ti/Pt diffusion barrier and Au cap were fabricated on n+ and p+-InGaAs, and the relationship between their specific contact resistance and interfacial chemistry was examined. Palladium-based contacts offered the lowest specific contact resistances of ρc=3.2×10−8 and 1.9×10−8 Ω-cm2 to n+- and p+-InGaAs, respectively. The low resistances of the Pd-based contact were correlated with the formation of a uniform PdxInGaAs phase in direct contact with InGaAs, as observed using transmission electron microscopy and energy dispersive spectroscopy. On the other hand, the Mo-based contact to n+ and p+-InGaAs had much higher specific contact resistances, even though its specific contact resistance on lightly doped n-InGaAs was nearly the same as that of the Pd-based contact. The cause of this discrepancy was identified to be the native oxide layer that remained between the contact and semiconductor in the Mo-based contacts, as revea...

Suzanne E. Mohney

Papers

Extracting the Richardson constant: IrOx/n-ZnO Schottky diodes

Oxidation of silicon nanowires for top-gated field effect transistors

Study of contact resistivity, mechanical integrity, and thermal stability of Ti/Al and Ta/Al ohmic contacts to n-type GaN

Formation of nickel germanide contacts to Ge nanowires

Characterization of low-resistance ohmic contacts to n- and p-type InGaAs