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

Wide-gap layered oxychalcogenide semiconductors: Materials, electronic structures and optoelectronic properties

A three-dimensional vertically-stacked flexible integrated circuit is demonstrated based on hybrid complementary inverters made of n-type In–Ga–Zn–O (a-IGZO) amorphous oxide thin-film transistors (TFTs) and p-type poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2) polymer TFTs, where all the fabrication processes were performed at temperatures ≤120 °C. Saturation mobilities of the a-IGZO TFT and the F8T2 TFT are ∼3.2 and ∼1.7×10−3 cm2 V−1 s−1, respectively, from which we chose the appropriate dimensions of the TFTs so as to obtain a good balance for the inverter operation. The maximum voltage gain is ∼67, which is better than those reported for organic/oxide hybrid complementary inverters.

Three-dimensionally stacked flexible integrated circuit: Amorphous oxide/polymer hybrid complementary inverter using n-type a-In–Ga–Zn–O and p-type poly-(9,9-dioctylfluorene-co-bithiophene) thin-film transistors

Device characteristics improvement of a-In–Ga–Zn–O TFTs by low-temperature annealing

Thermal field emission (TFE) from a flat surface of 12CaO∙7Al2O3 (C12A7) electride was examined at temperatures up to 900°C and applied external voltages of 0–6kV in a 10−5Pa vacuum. TFE started to occur at ∼650°C and steeply increased at ∼900°C to reach ∼80μA (∼1.5Acm−2) when an extraction field of 105Vcm−1 (an extraction voltage of 6kV) was applied. The work function estimated from the Richardson–Dushman equation was ∼2.1eV, which is rather smaller than that of LaB6 (∼2.7eV). It is experimentally confirmed that the emission with a current of ∼50μA (from a 80μm diameter area) was stably sustained for more than 90h. The efficient and stable emission at relatively low temperature in a moderate vacuum atmosphere strongly suggests that the C12A7 electride has high potential for TFE applications.

Intense thermal field electron emission from room-temperature stable electride

It has been considered that FeAs-based high-transition temperature (high-${T}_{\text{c}}$) superconductors need electron or hole doping by aliovalent-ion substitution or large off stoichiometry in order to induce superconductivity. We report that exposure of undoped ${\text{SrFe}}_{2}{\text{As}}_{2}$ epitaxial thin films to water vapor induces a superconducting transition. These films exhibit a higher onset ${T}_{\text{c}}$ (25 K) and larger magnetic field anisotropy than those of cobalt-doped ${\text{SrFe}}_{2}{\text{As}}_{2}$ epitaxial films, suggesting that the mechanism for the observed superconducting transition differs from that of the aliovalent-ion-doped ${\text{SrFe}}_{2}{\text{As}}_{2}$. The present finding provides an interesting approach to induce superconductivity with a higher ${T}_{\text{c}}$ in FeAs-based superconductors.

Toshio Kamiya

Papers

Wide-gap layered oxychalcogenide semiconductors: Materials, electronic structures and optoelectronic properties

Three-dimensionally stacked flexible integrated circuit: Amorphous oxide/polymer hybrid complementary inverter using n-type a-In–Ga–Zn–O and p-type poly-(9,9-dioctylfluorene-co-bithiophene) thin-film transistors

Device characteristics improvement of a-In–Ga–Zn–O TFTs by low-temperature annealing

Intense thermal field electron emission from room-temperature stable electride

Water-induced superconductivity in SrFe 2 As 2