There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers1. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H)2,3,4,5 and organic semiconductors2,6,7,8,9,10 have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven organic light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temperature and device performance. Here, we propose to solve this problem by using a novel semiconducting material—namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)—for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temperature and exhibits Hall effect mobilities exceeding 10 cm2 V-1 s-1, which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit saturation mobilities of 6–9 cm2 V-1 s-1, and device characteristics are stable during repetitive bending of the TTFT sheet.

Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors

We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.

Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05−0.12) with Tc = 26 K

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

This paper reviews recent progress in AOSs TFT technology and science. The origins of the low voltage operation and the large mobility are discussed in relation with subgap density of states and the density functional theory.

The origins of high mobility and low operation voltage of amorphous oxide channel TFTs

Among the intermetallics and alloys, YCu is an unusual material because it displays negative thermal expansion without spin ordering. The mechanism behind this behavior that is caused by the structural phase transition of YCu has yet to be fully understood. To gain insight into this mechanism, we experimentally examined the crystal structure of the low-temperature phase of YCu and discuss the origin of the phase transition with the aid of thermodynamics calculations. The result shows that the high-temperature (cubic CsCl-type) to low-temperature (orthorhombic FeB-type) structural phase transition is driven by the rearrangement of three covalent bonds, namely, Y–Cu, Y–Y, and Cu–Cu, which compete for the bonding energy and phonon entropy. At low temperatures, the mixing of Y and Cu does not take place easily because of the weak attractive force between these atoms expected from the small negative mixing enthalpy. This causes all three interactions to take part in the bonding, and Y and Cu are segregated to ...

On the Origin of the Negative Thermal Expansion Behavior of YCu.

Ionic materials like oxides have a variety of crystal/atomic structures owing to the coexistence of long-range Coulomb interaction and short-range covalent bonds, which often produce natural nanostructures embedded in their crystal structures. Such structures and materials can be sources of unusual electronic structures and nonconventional materials properties and functions. This chapter reviews such exotic crystal structures in relation to their electronic structures and properties. It will be discussed for what applications such oxides can have advantages over the conventional functional materials such as Si.

Exotic Crystal Structures and Electronic Structures in Novel Structured Inorganic Materials

Thin-film-coated conductors of the iron-based superconductor BaFe2(As1-xPx)2 (Ba122:P) were fabricated on polycrystalline metal-tape substrates with two different misorientation grain-boundary angles (well aligned (4 deg.) and poorly aligned (8 deg.)) by pulsed laser deposition. The poorly aligned sample is not applicable to cuprate-coated conductors because in-plane misorientation angles above 4 deg. result in exponential decay of the critical current density (Jc). The Ba122:P film exhibited higher Jc with stronger vortex pinning when grown on the poorly aligned substrate than on the well-aligned substrate even though the crystallinity was poorer. It was revealed that the misorientation angles of the poorly aligned samples were less than 6 deg., which are less than the critical angle of iron-based superconductors (~9 deg.), and the strong pinning is attributed to the high-density low misorientation angle grain boundaries. This result demonstrates a distinct advantage over cuprate-coated conductors because well-aligned metal-tape substrates are not necessary for practical applications of these iron-based superconductors.

Toshio Kamiya

Papers

The origins of high mobility and low operation voltage of amorphous oxide channel TFTs

On the Origin of the Negative Thermal Expansion Behavior of YCu.

Exotic Crystal Structures and Electronic Structures in Novel Structured Inorganic Materials

High critical-current in iron-based superconductor thin-films on metal tapes arising from large misorientation grain boundaries

15.1: Invited Paper: Understanding and controlling electronic defects in amorphous oxide semiconductor